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Currently, I have a 9kW Mira shower at the end of about 9m of 6mm2 cable on a 32amp circuit breaker. The cable is clipped to walls (garage, bedroom cupboard) over about half its length, the other half is running against loft insulation.
I'd like to move the double pole switch (ceiling pull cord) across the room. To do this I'd be adding via a junction box about an extra 3m of cable in the loft making it a 12m run from the consumer unit.
Is this safe? Will my house burn down?
A scan of the DIY forums suggest it *should* be fine but these days most recomend 10mm2 cable.
Retro fitting 10mm2 cable and a 45amp breaker would be a much bigger, more expensive job that I'd only do if the 6mm2 cable really is unsafe.
Thanks in advance for any experienced thoughts.
Post edited at 20:17
In reply to JLS:
No, you'll be fine. Go ahead and do it, as long as you're capable, you'll be ok.
............Oh, and don't listen the naysayers that will say you will not only burn your own house down, but you will also bring the whole National Grid down as well.
.........Or Electrocute your visitors.
.........Having a shower, swinging on a corded pull cord switch.
No, you'll be fine. Go ahead and do it, as long as you're capable, you'll be ok.
............Oh, and don't listen the naysayers that will say you will not only burn your own house down, but you will also bring the whole National Grid down as well.
.........Or Electrocute your visitors.
.........Having a shower, swinging on a corded pull cord switch.
Post edited at 20:49
In reply to JLS: I believe wiring in a bathroom is covered by specific regs and should be performed or certified by a qualified person. Only probably an issue if you are selling the house or you electrocute your visitors maybe?
In reply to JLS:
Your present set-up is only good for about 7kW. You should already be on 10mm2 and 45A breaker.
Your present set-up is only good for about 7kW. You should already be on 10mm2 and 45A breaker.
5
In reply to JLS:
A new breaker and 10mm cable isn't that expensive and isn't complicated. If you are going to mess around with your electrics you may as well do it properly.
While you are at it make sure your switch is the correct rating as well.
A new breaker and 10mm cable isn't that expensive and isn't complicated. If you are going to mess around with your electrics you may as well do it properly.
While you are at it make sure your switch is the correct rating as well.
Post edited at 21:12
2
In reply to JLS:
Brilliant.
For 3m of cable the guy now needs to rewire his whole shower circuit. What would happen if he was shortening it back 3 m ??
Brilliant.
For 3m of cable the guy now needs to rewire his whole shower circuit. What would happen if he was shortening it back 3 m ??
Post edited at 21:20
1
In reply to arch:
He has asked for expert advice and been advised that he is already outside code, ( and i suspect that may have implications for his insurance. )
Good advice , I say, and if it was me, I would either swap my shower for a 7kw, or , more likely spend a similar amount of money on upgrading the wiring ( 3 m longer) using the existing shower, and be in code, and be without risk of infringing his insurance.
Edit,
30-40 quid for 10mm2 cable,
MCB 5-10 quid
Pull switch 7-15
Cheaper than a 7kw shower.
> Brilliant.
> For 3m of cable the guy now needs to rewire his whole shower circuit. What would happen if he was shortening it back 3 m ??
He has asked for expert advice and been advised that he is already outside code, ( and i suspect that may have implications for his insurance. )
Good advice , I say, and if it was me, I would either swap my shower for a 7kw, or , more likely spend a similar amount of money on upgrading the wiring ( 3 m longer) using the existing shower, and be in code, and be without risk of infringing his insurance.
Edit,
30-40 quid for 10mm2 cable,
MCB 5-10 quid
Pull switch 7-15
Cheaper than a 7kw shower.
Post edited at 21:42
4
In reply to arch:
It's about a 25% increase in cable length, and cable length is very significant when calculating current and loadings which in turn have an impact on cable size and safe loading.
Imagine a pipe which has a tap that demands a certain flow of water. If the pipe is physically too small to supply it, yet the tap continues to pull, the pipe will be over capacity, and any pinhole weakness will split, like when people change from a trad boiler to a mains pressure combi boiler in an 80's house.
In an electric cable this will equate to overheating, which could go unnoticed, or could get neighbouring materials hot, or could make a switch melt, or blow a circuit breaker or cause a fire.
Electrics are easy in some circumstances, but the complexities are often underrated and overlooked!
Btw, shortened cable will lead to less resistance and therefore a reduced loading. I'm not an electrician but have a rudimentary appreciation and have seen the worst results of bodged jobs and have regularly come across miscalculated cable loadings causing shorts once old fuses are switched to mcb's.
It's about a 25% increase in cable length, and cable length is very significant when calculating current and loadings which in turn have an impact on cable size and safe loading.
Imagine a pipe which has a tap that demands a certain flow of water. If the pipe is physically too small to supply it, yet the tap continues to pull, the pipe will be over capacity, and any pinhole weakness will split, like when people change from a trad boiler to a mains pressure combi boiler in an 80's house.
In an electric cable this will equate to overheating, which could go unnoticed, or could get neighbouring materials hot, or could make a switch melt, or blow a circuit breaker or cause a fire.
Electrics are easy in some circumstances, but the complexities are often underrated and overlooked!
Btw, shortened cable will lead to less resistance and therefore a reduced loading. I'm not an electrician but have a rudimentary appreciation and have seen the worst results of bodged jobs and have regularly come across miscalculated cable loadings causing shorts once old fuses are switched to mcb's.
Post edited at 21:36
3
In reply to JLS:
Just interested, as the installation is incorrectly rated, have you checked if it is properly bonded, and RCD protected ?
http://www.mirashowers.co.uk/common/pdf/Miras-Guide-to-Electric-Showers.pdf
Just interested, as the installation is incorrectly rated, have you checked if it is properly bonded, and RCD protected ?
http://www.mirashowers.co.uk/common/pdf/Miras-Guide-to-Electric-Showers.pdf
In reply to Jim C:
As I completed my C&G 236 Electrical Installation part 1 and 2 Apprenticeship in 1985 at Loughborough college and have worked In the Electrical industry ever since, i'd say I know what i'm talking about.
...............You ??
As I completed my C&G 236 Electrical Installation part 1 and 2 Apprenticeship in 1985 at Loughborough college and have worked In the Electrical industry ever since, i'd say I know what i'm talking about.
...............You ??
Post edited at 21:57
In reply to Jim C:
Yeah, I'm not overly worried about the cost, though the cheapest cable I can find is about £60 for 16m from Wickes.
It's just the bloody hassle of laying the cable, though to be fair it doesn't *look* difficult as the cable is mostly exposed.
Yeah, I'm not overly worried about the cost, though the cheapest cable I can find is about £60 for 16m from Wickes.
It's just the bloody hassle of laying the cable, though to be fair it doesn't *look* difficult as the cable is mostly exposed.
In reply to arch:
I know you are probably correct but I think I'll just bite the bullet and put in the 10mm cable.
The truth becomes what the majority think even when they are wrong.
I know you are probably correct but I think I'll just bite the bullet and put in the 10mm cable.
The truth becomes what the majority think even when they are wrong.
In reply to arch:
I think you may have mistaken me with someone who said you did not know what you were talking about. I have not challenged anything you have said ( because I had not read it at the time )
I was simply agreeing with Jim Fraser t, ( having consulted his shower manufactures guidelines, which I linked ) that his shower appeared to be overrated for the 6mm2 cabling.
Not a qualified electrician, I did rewire my 1903 home - which was all lead cable at the time - ( some years back it has got to be said) including the shower, outside lighting, power to my shed, fire alarms etc. Which I have since upgraded to keep up with new regs.
The inspector who signed it off( to the code at the time ) was quite rightly strict, and had a couple of 'observations' , but otherwise happy, and said what you said , (as long as I was capable )
If you are saying( in you expert opinion) that the 9kw shower, on a 9m of 6mm2 cable is OK to extend, who am I to argue.
I think you may have mistaken me with someone who said you did not know what you were talking about. I have not challenged anything you have said ( because I had not read it at the time )
I was simply agreeing with Jim Fraser t, ( having consulted his shower manufactures guidelines, which I linked ) that his shower appeared to be overrated for the 6mm2 cabling.
Not a qualified electrician, I did rewire my 1903 home - which was all lead cable at the time - ( some years back it has got to be said) including the shower, outside lighting, power to my shed, fire alarms etc. Which I have since upgraded to keep up with new regs.
The inspector who signed it off( to the code at the time ) was quite rightly strict, and had a couple of 'observations' , but otherwise happy, and said what you said , (as long as I was capable )
If you are saying( in you expert opinion) that the 9kw shower, on a 9m of 6mm2 cable is OK to extend, who am I to argue.
In reply to peterjb:
Wrong.
A longer cable at the same size will increase the resistance, reduce the voltage at the shower unit, and therefore reduce the current draw (load on the CU).
Extending the cable will effectively make it safer, although may reduce the performance.
It may not conform to regs, but it won't burn his house down.
> Btw, shortened cable will lead to less resistance and therefore a reduced loading.
Wrong.
A longer cable at the same size will increase the resistance, reduce the voltage at the shower unit, and therefore reduce the current draw (load on the CU).
Extending the cable will effectively make it safer, although may reduce the performance.
It may not conform to regs, but it won't burn his house down.
1
In reply to JLS:
I see you're getting some highly variable advice here, particularly that post from peterjb which is just plain wrong in every paragraph.
Firstly, as others have said, bathrooms are "special" in the regs and you really shouldn't DIY it. That said many people do, and safely too.
Extending your cable will not cause more current to flow. It will add total circuit resistance and hence *reduce* the current. Your shower will perform slightly worse (probably too little for you to notice) and the *total* heat generated in the cabling will increase but it will be over the now longer length and so the cable will be cooler.
The most likely problem, as in the thing to look out for, is the terminals of the new junction box. Anything other than a nice clean, well made connection can have a significant resistance and at the currents involved that can lead to localised overheating which at best isn't good and at worst can cause a fire.
Clearly the existing cabling is working fine. It's a marginal call as to whether it's rated as adequate and because it's a boundary case the sums are tricky. Not that the maths is hard but you need to estimate the effect of local conditions, especially the nearby insulation, and that's a judgement call which requires experience. If you have the option of moving the insulation away from the cable do so.
Any new cable you are adding really should be 10mm though, there would be no excuse for using 6mm.
So in summary I couldn't possibly tell you how to proceed but here's what I might expect someone in your position to do, and I wouldn't wince if I came across it:
Have someone use the shower and after a few minutes feel the existing cable in a section covered by the insulation. If it's appreciably warm you probably want to consider replacing it.
Assuming all's good, add a junction box and new 10mm cable, ensuring it's in free air and not insulated. Take care with the terminals.
Enjoy.
I see you're getting some highly variable advice here, particularly that post from peterjb which is just plain wrong in every paragraph.
Firstly, as others have said, bathrooms are "special" in the regs and you really shouldn't DIY it. That said many people do, and safely too.
Extending your cable will not cause more current to flow. It will add total circuit resistance and hence *reduce* the current. Your shower will perform slightly worse (probably too little for you to notice) and the *total* heat generated in the cabling will increase but it will be over the now longer length and so the cable will be cooler.
The most likely problem, as in the thing to look out for, is the terminals of the new junction box. Anything other than a nice clean, well made connection can have a significant resistance and at the currents involved that can lead to localised overheating which at best isn't good and at worst can cause a fire.
Clearly the existing cabling is working fine. It's a marginal call as to whether it's rated as adequate and because it's a boundary case the sums are tricky. Not that the maths is hard but you need to estimate the effect of local conditions, especially the nearby insulation, and that's a judgement call which requires experience. If you have the option of moving the insulation away from the cable do so.
Any new cable you are adding really should be 10mm though, there would be no excuse for using 6mm.
So in summary I couldn't possibly tell you how to proceed but here's what I might expect someone in your position to do, and I wouldn't wince if I came across it:
Have someone use the shower and after a few minutes feel the existing cable in a section covered by the insulation. If it's appreciably warm you probably want to consider replacing it.
Assuming all's good, add a junction box and new 10mm cable, ensuring it's in free air and not insulated. Take care with the terminals.
Enjoy.
2
1
In reply to csambrook:
I do wish people could either explain this one accurately, or not at all. (Having said that, I'll probably explain it wrongly now!)
Bathrooms are not special. Areas with a region 2.25 m vertically and 0.60 m horizontally of a bath or shower head are special. Special does not mean "you really shouldn't DIY it." Special means notifiable, which means that if you DIY it, you then have to pay to have Building Control or a registered 3rd party visit to sign off on your work. You should also check the small print of your home insurance policy to see what it says with regards certification, and if they want copies of certificates on file.
https://www.niceic.com/Niceic.com/media/Schemes/NICEIC-Part-P-Updated-Facts...
https://www.elecsa.co.uk/Documents/Public-Documents/Contractors/Notifiable-...
> Firstly, as others have said, bathrooms are "special" in the regs and you really shouldn't DIY it. That said many people do, and safely too.
I do wish people could either explain this one accurately, or not at all. (Having said that, I'll probably explain it wrongly now!)
Bathrooms are not special. Areas with a region 2.25 m vertically and 0.60 m horizontally of a bath or shower head are special. Special does not mean "you really shouldn't DIY it." Special means notifiable, which means that if you DIY it, you then have to pay to have Building Control or a registered 3rd party visit to sign off on your work. You should also check the small print of your home insurance policy to see what it says with regards certification, and if they want copies of certificates on file.
https://www.niceic.com/Niceic.com/media/Schemes/NICEIC-Part-P-Updated-Facts...
https://www.elecsa.co.uk/Documents/Public-Documents/Contractors/Notifiable-...
2
1
In reply to csambrook:
Personally I wouldn't mix cable sizes.
The next person to look at it decides they want a nicer shower with more KW looks at the nice bit of 10mm2 and doesn't realise it isn't all the way.
Another reason I suggested doing it properly with 10mm2 its ready for an upgraded shower in future.
If I was to extend I would stick with 6mm2 like the rest of it and route it somewhere away from the insulation.
Personally I wouldn't mix cable sizes.
The next person to look at it decides they want a nicer shower with more KW looks at the nice bit of 10mm2 and doesn't realise it isn't all the way.
Another reason I suggested doing it properly with 10mm2 its ready for an upgraded shower in future.
If I was to extend I would stick with 6mm2 like the rest of it and route it somewhere away from the insulation.
4
In reply to Hooo:
Peter said a shorter cable is less resistance. (Presumably in reply to the comment about would we tell him to upgrade if he was making it shorter)
He isnt wrong, you didn't read it right.
> Wrong.
> A longer cable at the same size will increase the resistance
Peter said a shorter cable is less resistance. (Presumably in reply to the comment about would we tell him to upgrade if he was making it shorter)
He isnt wrong, you didn't read it right.
In reply to JLS:
What a thread! I wonder what a Part P assessor or college tutor would think...
Right, wrong, ambiguous, pedantic, well meaning, useless etc etc.
Sighs.
What a thread! I wonder what a Part P assessor or college tutor would think...
Right, wrong, ambiguous, pedantic, well meaning, useless etc etc.
Sighs.
3
1
In reply to JLS:
The current 6mm cable is protected as it is by the 32A MCB, extending it 3M is ok. As started above, for the shower you have you should be using 10mm and a larger breaker, however if you continue with your current setup the worst that will happen is nuisance tripping of the mcb. The MCB is there to provide over current protection for the cable.
However, any circuits supplying a bathroom should be RCD protected, so this should be verified and that it operates correctly.
If you change the mcb and upgrade the cable then this work becomes notifiable to LABC and you must be able to prove competence and the ability to test to bs7671.
Feel free to pm me for more info
The current 6mm cable is protected as it is by the 32A MCB, extending it 3M is ok. As started above, for the shower you have you should be using 10mm and a larger breaker, however if you continue with your current setup the worst that will happen is nuisance tripping of the mcb. The MCB is there to provide over current protection for the cable.
However, any circuits supplying a bathroom should be RCD protected, so this should be verified and that it operates correctly.
If you change the mcb and upgrade the cable then this work becomes notifiable to LABC and you must be able to prove competence and the ability to test to bs7671.
Feel free to pm me for more info
2
In reply to JLS:
Also, with regards extending it, I would use Wago terminals in an adaptable plastic enclosure, they now to a terminal which will accept 6mm cable.
Also, with regards extending it, I would use Wago terminals in an adaptable plastic enclosure, they now to a terminal which will accept 6mm cable.
In reply to marsbar:
Er, no. He actually said:
"Btw, shortened cable will lead to less resistance and therefore a reduced loading."
While he is correct that a shortened cable will have less resistance he is incorrect to then go on to say that the load is reduced. The load is *increased*, less total resistance means more current flowing and *more* load.
He also gets it wrong the other way around a couple of paragraphs earlier when he says that extra resistance will mean overheating. Yes, overheating of cable is something to avoid and is caused by the cable being underrated for the situation it's in but adding resistance will not cause this and in fact will improve the situation.
It's pretty marginal but adding 3m of cable is going to make the whole installation safer by reducing the current flow and reducing the heating in the cable. It will make the shower performance worse although again, not by very much at all.
> Peter said a shorter cable is less resistance. (Presumably in reply to the comment about would we tell him to upgrade if he was making it shorter)
> He isnt wrong, you didn't read it right.
> He isnt wrong, you didn't read it right.
Er, no. He actually said:
"Btw, shortened cable will lead to less resistance and therefore a reduced loading."
While he is correct that a shortened cable will have less resistance he is incorrect to then go on to say that the load is reduced. The load is *increased*, less total resistance means more current flowing and *more* load.
He also gets it wrong the other way around a couple of paragraphs earlier when he says that extra resistance will mean overheating. Yes, overheating of cable is something to avoid and is caused by the cable being underrated for the situation it's in but adding resistance will not cause this and in fact will improve the situation.
It's pretty marginal but adding 3m of cable is going to make the whole installation safer by reducing the current flow and reducing the heating in the cable. It will make the shower performance worse although again, not by very much at all.
1
1
In reply to marsbar:
A very good point. I'd looked at it from a purely electrical safety POV but you're right, it's important to also consider the human factors and to avoid obvious mistakes in the future.
> Personally I wouldn't mix cable sizes.
> The next person to look at it decides they want a nicer shower with more KW looks at the nice bit of 10mm2 and doesn't realise it isn't all the way.
> If I was to extend I would stick with 6mm2 like the rest of it and route it somewhere away from the insulation.
> The next person to look at it decides they want a nicer shower with more KW looks at the nice bit of 10mm2 and doesn't realise it isn't all the way.
> If I was to extend I would stick with 6mm2 like the rest of it and route it somewhere away from the insulation.
A very good point. I'd looked at it from a purely electrical safety POV but you're right, it's important to also consider the human factors and to avoid obvious mistakes in the future.
1
In reply to wintertree:
Both those documents relate to England. JLS is in Scotland so perhaps the relevant documents there would be more applicable. I work with the Scottish Reg.s on a daily basis (and liaise with English architects working on Scottish projects who get caught out regularly) and know there are some big differences between the two.
> I do wish people could either explain this one accurately, or not at all. (Having said that, I'll probably explain it wrongly now!)
Both those documents relate to England. JLS is in Scotland so perhaps the relevant documents there would be more applicable. I work with the Scottish Reg.s on a daily basis (and liaise with English architects working on Scottish projects who get caught out regularly) and know there are some big differences between the two.
In reply to Fraser:
As that wasn't stated I suspect more then a few people replying didn't know that. Feel free to explain the situation in Scotland...
> . JLS is in Scotland so perhaps the relevant documents there would be more applicable
As that wasn't stated I suspect more then a few people replying didn't know that. Feel free to explain the situation in Scotland...
In reply to peterjb:
Straight (not coiled or bundled) cables will tend to dissipate more heat the longer they get but as they also have more cooling area the temperature doesn't change.
This analogy makes no sense from an electrical or a plumbing perspective.
Erm... are you sure about that?
OP: Personally I'd just move the switch on the existing cable or extend it with the same size cable as the rest of the circuit. Check the regs to make sure you're routing the cable safely and locating the switch somewhere safe.
jk (not an electrician either)
> It's about a 25% increase in cable length, and cable length is very significant when calculating current and loadings which in turn have an impact on cable size and safe loading.
Straight (not coiled or bundled) cables will tend to dissipate more heat the longer they get but as they also have more cooling area the temperature doesn't change.
> Imagine a pipe which has a tap that demands a certain flow of water. If the pipe is physically too small to supply it, yet the tap continues to pull, the pipe will be over capacity, and any pinhole weakness will split, like when people change from a trad boiler to a mains pressure combi boiler in an 80's house.
This analogy makes no sense from an electrical or a plumbing perspective.
> Btw, shortened cable will lead to less resistance and therefore a reduced loading.
Erm... are you sure about that?
OP: Personally I'd just move the switch on the existing cable or extend it with the same size cable as the rest of the circuit. Check the regs to make sure you're routing the cable safely and locating the switch somewhere safe.
jk (not an electrician either)
1
In reply to Jim C:
I didn't think house buildings policies usually excluded fire damage as a result of botched diy?
> ( and i suspect that may have implications for his insurance. )
I didn't think house buildings policies usually excluded fire damage as a result of botched diy?
In reply to JLS:
Can you describe this part of the cable run in more detail, or even better, post a picture up somewhere?
> ... the other half is running against loft insulation.
Can you describe this part of the cable run in more detail, or even better, post a picture up somewhere?
In reply to marsbar:
I am totally confused now. Does a longer cable mean more or less resistance?
Not load or anything else.
Is the resistance important in the scale of things?
I thought that it was the heat that was the issue, therefore the current and the surroundings were the main considerations.
The reference I had suggests 6 might be ok on a wall but not in with insulation.
I am totally confused now. Does a longer cable mean more or less resistance?
Not load or anything else.
Is the resistance important in the scale of things?
I thought that it was the heat that was the issue, therefore the current and the surroundings were the main considerations.
The reference I had suggests 6 might be ok on a wall but not in with insulation.
In reply to marsbar:
Resistance is proportional to length. It's of virtually no interest in this case.
Heat is the problem and if it's covered by insulation, it fails miserably!
Hence clarification requested.
Resistance is proportional to length. It's of virtually no interest in this case.
Heat is the problem and if it's covered by insulation, it fails miserably!
Hence clarification requested.
In reply to wintertree:
http://electrical.theiet.org/building-regulations/scotland-n-ireland/
http://www.gov.scot/Topics/Built-Environment/Building/Building-standards
http://www.electricalsafetyfirst.org.uk/guides-and-advice/building-regulati...
https://www.niceic.com/join-us/scotland-schemes
http://electrical.theiet.org/building-regulations/scotland-n-ireland/
http://www.gov.scot/Topics/Built-Environment/Building/Building-standards
http://www.electricalsafetyfirst.org.uk/guides-and-advice/building-regulati...
https://www.niceic.com/join-us/scotland-schemes
Post edited at 16:25
In reply to Lusk:
Well. Except that the resistance is proportional to the temperature. So as the temperature rises, so does the resistance. And it's the resistance that causes the heat in the first place.
> Resistance is proportional to length. It's of virtually no interest in this case.
> Heat is the problem and if it's covered by insulation, it fails miserably!
> Hence clarification requested.
Well. Except that the resistance is proportional to the temperature. So as the temperature rises, so does the resistance. And it's the resistance that causes the heat in the first place.
1
In reply to Lusk:
Careful with that Lusk. Resistance is also a function of cable cross-sectional area and is the very reason for using a bigger cable CSA, the lower resistance of a bigger CSA means less heating.
6mm Twin and Earth (which is probably what we're talking about here) is pretty marginal in this installation. It is rated at somewhere between 32A and 46A depending on the situation. The 9kW shower takes 39A.
10mm T&E is rated at between 43A and 63A so would be wonderful. But that's not what we've got to start with.
Our OP has an installation which is working fine. Let's assume that the original installer did his job properly and the cable is free enough of insulation that it's OK with 39A. Extending the cable, even with more 6mm T&E, is not going to make matters any worse. It will in fact make things ever so slightly better from a heating point of view but not by enough to get excited about.
There are some considerations concerning fault conditions and generating enough current to guarantee a circuit breaker trip under those conditions but a 3m extension to the cable is short enough that this should not be a problem.
Now back to the real world. I strongly suspect that the original installer didn't consider the effect of the insulation or that it was added afterwards. My guess would be (and yours too by the sound of it) that the existing 6mm cable is running really quite close to it's limit. It's probably getting a bit too hot but the saving grace will be that showers don't run continuously (except when my daughter is in ours) and it will cool again between periods of use.
Hence my suggestion that the OP feels the cable after the shower has been used for a bit. If it's warm then that might provide a very practical demonstration that the 6mm is not really up to the job, at least with insulation covering it.
But all of that said, the original question was about whether it's OK to extend the cable. And the answer to that is YES. It will make it no worse than it currently is.
> Resistance is proportional to length. It's of virtually no interest in this case.
> Heat is the problem and if it's covered by insulation, it fails miserably!
> Hence clarification requested.
> Heat is the problem and if it's covered by insulation, it fails miserably!
> Hence clarification requested.
Careful with that Lusk. Resistance is also a function of cable cross-sectional area and is the very reason for using a bigger cable CSA, the lower resistance of a bigger CSA means less heating.
6mm Twin and Earth (which is probably what we're talking about here) is pretty marginal in this installation. It is rated at somewhere between 32A and 46A depending on the situation. The 9kW shower takes 39A.
10mm T&E is rated at between 43A and 63A so would be wonderful. But that's not what we've got to start with.
Our OP has an installation which is working fine. Let's assume that the original installer did his job properly and the cable is free enough of insulation that it's OK with 39A. Extending the cable, even with more 6mm T&E, is not going to make matters any worse. It will in fact make things ever so slightly better from a heating point of view but not by enough to get excited about.
There are some considerations concerning fault conditions and generating enough current to guarantee a circuit breaker trip under those conditions but a 3m extension to the cable is short enough that this should not be a problem.
Now back to the real world. I strongly suspect that the original installer didn't consider the effect of the insulation or that it was added afterwards. My guess would be (and yours too by the sound of it) that the existing 6mm cable is running really quite close to it's limit. It's probably getting a bit too hot but the saving grace will be that showers don't run continuously (except when my daughter is in ours) and it will cool again between periods of use.
Hence my suggestion that the OP feels the cable after the shower has been used for a bit. If it's warm then that might provide a very practical demonstration that the 6mm is not really up to the job, at least with insulation covering it.
But all of that said, the original question was about whether it's OK to extend the cable. And the answer to that is YES. It will make it no worse than it currently is.
1
In reply to JLS:
A 9kw shower will only pull 39a when it is on full blast. (If you can stand it that is) That's also assuming the supply voltage is 230v. The maximum allowed voltage is 253v so the ampage could be lower. It would also be interesting to see how many amps the shower is drawing when a "Normal" water temperature is being used.
A 9kw shower will only pull 39a when it is on full blast. (If you can stand it that is) That's also assuming the supply voltage is 230v. The maximum allowed voltage is 253v so the ampage could be lower. It would also be interesting to see how many amps the shower is drawing when a "Normal" water temperature is being used.
1
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In reply to arch:
Nooooooooo. That's not how it works at all. The resistance of the heater doesn't magically go up to compensate for an increased supply voltage. Of course it stays the same and *more* current flows (I=V/R), effectively the 9kW shower becomes a 9.something kW shower.
Now manufacturers of course play games at the design stage and the 9kW probably isn't exactly 9kW at all but you have to base your calcs on something so you use the stated power and the nominal line voltage.
When sizing cable you need to allow for the worst case, which is the shower on "full blast". Of course it will be used at full power, provided the water supply is up to delivering enough water to cool the elements it will simply be turned up so that the temperature is lovely and the volume of water is max'd out. Clearly you've not met my daughter.
> A 9kw shower will only pull 39a when it is on full blast. (If you can stand it that is) That's also assuming the supply voltage is 230v. The maximum allowed voltage is 253v so the ampage could be lower. It would also be interesting to see how many amps the shower is drawing when a "Normal" water temperature is being used.
Nooooooooo. That's not how it works at all. The resistance of the heater doesn't magically go up to compensate for an increased supply voltage. Of course it stays the same and *more* current flows (I=V/R), effectively the 9kW shower becomes a 9.something kW shower.
Now manufacturers of course play games at the design stage and the 9kW probably isn't exactly 9kW at all but you have to base your calcs on something so you use the stated power and the nominal line voltage.
When sizing cable you need to allow for the worst case, which is the shower on "full blast". Of course it will be used at full power, provided the water supply is up to delivering enough water to cool the elements it will simply be turned up so that the temperature is lovely and the volume of water is max'd out. Clearly you've not met my daughter.
1
1
In reply to arch:
I always needed my old electric shower on full power in cold weather.
I agree with you that 6mm2 will probably be fine, but if it was mine I would upgrade while I was at it.
My electric shower was in 6mm. It worked fine despite being wired via the cooker and the burglar alarm had been spured off. You have to laugh....
I always needed my old electric shower on full power in cold weather.
I agree with you that 6mm2 will probably be fine, but if it was mine I would upgrade while I was at it.
My electric shower was in 6mm. It worked fine despite being wired via the cooker and the burglar alarm had been spured off. You have to laugh....
1
In reply to Jim Hamilton:
My wife is a at home childminder Jim , and we had to do some specific electrical work to get any cover. ( that may or may not be the case for 'normal' insurance, but just asking the OP to check his insurance , as I don't know his homes insurance status.
It is also waste of money paying for a policy that the insurers can just walk away from you on a ' technicality'
The main stipulation I remember was the installation of mains wired ( battery back up fire alarms ( with lights)
They had to be wired so that they were always LIVE even if the RCD tripped the house.
My assessment is, if we had a fire, and we had not done the mains fire alarm work ( and certified it) they would say we were not covered.
My wife is a at home childminder Jim , and we had to do some specific electrical work to get any cover. ( that may or may not be the case for 'normal' insurance, but just asking the OP to check his insurance , as I don't know his homes insurance status.
It is also waste of money paying for a policy that the insurers can just walk away from you on a ' technicality'
The main stipulation I remember was the installation of mains wired ( battery back up fire alarms ( with lights)
They had to be wired so that they were always LIVE even if the RCD tripped the house.
My assessment is, if we had a fire, and we had not done the mains fire alarm work ( and certified it) they would say we were not covered.
In reply to JLS:
JLS. Just extend the existing wire. It'll be fine.
I can't be arsed with all this tit for tat, my post is better than your post shit.........
JLS. Just extend the existing wire. It'll be fine.
I can't be arsed with all this tit for tat, my post is better than your post shit.........
1
In reply to marsbar:
When I first moved in to my 1903 house, I found a missing socket, covered by a square of rubber held to the skirting with drawing pins.
On removing the rubber, bare wires were revealed, not even a bit of insulating tape on them.
I decided to investigate further, so I found the trapdoor, and on lowering my feet into it, I found that we had deep foundations ( 3 feet) However, the first 8" was under water! ( a 'feature' of the seasonal water table around this area as I was to find.
Clutching my torch, I waded along to find that all the cabling was old lead covered, it was not secured anywhere anywhere, but to the sockets , and so the full weight of the cable was then pulling on that connection.
The wiring between the sockets hung down in long loops, and in some places there was a ' tide mark' on the wires from the times of the year that the water table was highest, so the old ( decaying) lead cables were actually dangling in the water for decades.
I was not laughing.
I immediately moved the wife and kids out ( to the in-laws) and rewired the whole place .
And added central heating whilst I was at it.
In hindsight, having the house empty to do the wiring and Heating was a godsend, the mess of 8o odd year old year old plaster walls/ ceilings turning to dust when wraggled was horrendous , even with an empty house.
> My electric shower was in 6mm. It worked fine despite being wired via the cooker and the burglar alarm had been spured off. You have to laugh....
When I first moved in to my 1903 house, I found a missing socket, covered by a square of rubber held to the skirting with drawing pins.
On removing the rubber, bare wires were revealed, not even a bit of insulating tape on them.
I decided to investigate further, so I found the trapdoor, and on lowering my feet into it, I found that we had deep foundations ( 3 feet) However, the first 8" was under water! ( a 'feature' of the seasonal water table around this area as I was to find.
Clutching my torch, I waded along to find that all the cabling was old lead covered, it was not secured anywhere anywhere, but to the sockets , and so the full weight of the cable was then pulling on that connection.
The wiring between the sockets hung down in long loops, and in some places there was a ' tide mark' on the wires from the times of the year that the water table was highest, so the old ( decaying) lead cables were actually dangling in the water for decades.
I was not laughing.
I immediately moved the wife and kids out ( to the in-laws) and rewired the whole place .
And added central heating whilst I was at it.
In hindsight, having the house empty to do the wiring and Heating was a godsend, the mess of 8o odd year old year old plaster walls/ ceilings turning to dust when wraggled was horrendous , even with an empty house.
Post edited at 20:33
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In reply to Jim C:
Not good. Mine is 1970s and mostly fine if a little dated.
I remember at the age of about 6 spending several weeks living at my Aunties house for similar reasons immediately after a house move, although I think that was planned or sort of.
Not good. Mine is 1970s and mostly fine if a little dated.
I remember at the age of about 6 spending several weeks living at my Aunties house for similar reasons immediately after a house move, although I think that was planned or sort of.
In reply to JLS:
Why ask for advise on this forum? there seems to be too many experts on here who think they know the upto date regs. Get a couple of estimates off part P electricians and compare prices and advice directly from someone who is up to date.
Mark
Why ask for advise on this forum? there seems to be too many experts on here who think they know the upto date regs. Get a couple of estimates off part P electricians and compare prices and advice directly from someone who is up to date.
Mark
In reply to JLS:
Seeing as the existing cable is maybe a bit close to it's limit where it is covered by insulation and maybe if it is bundled up with other cables anywhere. I'd consider checking the routing of the cable, separating the cable from others, and clipping it directly the building fabric to maximise heat dissipation and the theoretical maximum safe load for the cable.
Seeing as the existing cable is maybe a bit close to it's limit where it is covered by insulation and maybe if it is bundled up with other cables anywhere. I'd consider checking the routing of the cable, separating the cable from others, and clipping it directly the building fabric to maximise heat dissipation and the theoretical maximum safe load for the cable.
> JLS. Just extend the existing wire. It'll be fine.
> I can't be arsed with all this tit for tat, my post is better than your post shit.........
In reply to arch:
Dont be like that there's volt drop, disconnected times, and so on yet.
OP . Can you get the new [you are rewiring ? yes ] 16mm2 installed and keep the bending within the allowed radii / you may need to use a busbar.
did you say its in the garage ? need SWA ------------ pos
In reply to arch:
It takes quite a long time at 39A to trip a 32A breaker. Longer than a shower takes.
Plus, it won't be drawing 39A, because with all that 6mm2 between it and the CU it won't be getting 240V.
> So why isn't the 32A MCB tripping then ??
It takes quite a long time at 39A to trip a 32A breaker. Longer than a shower takes.
Plus, it won't be drawing 39A, because with all that 6mm2 between it and the CU it won't be getting 240V.
In reply to arch:
As Hooo has said it takes a looong time to trip a 32A MCB at 39A. Quite possibly forever.
A type B MCB, which is probably what's fitted, is specified to trip when the overload reaches a set level. Wait for it... between 3 and 5 times full load current. Bit of a shocker that isn't it, you might end up with 150A before the MCB trips!
> So why isn't the 32A MCB tripping then ??
As Hooo has said it takes a looong time to trip a 32A MCB at 39A. Quite possibly forever.
A type B MCB, which is probably what's fitted, is specified to trip when the overload reaches a set level. Wait for it... between 3 and 5 times full load current. Bit of a shocker that isn't it, you might end up with 150A before the MCB trips!
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In reply to Jim C:
You're describing exactly the situation under my floor except at some point it's been switched to big loops of PVC twin and earth that trails through the flood along with the big unsecured (and now isolated) loops of gas plumbing. The old lead cable is clipped up neatly high and dry though presumably the rubber had perished and started smoking by the 80s when the clown rewired. The gas fires were gaffa-taped to the chimneys when we moved in and one was leaking gas. How it hadn't killed the previous owners one way or another I don't know. I'm still nervous when cutting out the lead wiring in case some knobber has left a length of it live somehow.
jk
> Clutching my torch, I waded along to find that all the cabling was old lead covered, it was not secured anywhere anywhere, but to the sockets , and so the full weight of the cable was then pulling on that connection.
> The wiring between the sockets hung down in long loops, and in some places there was a ' tide mark' on the wires from the times of the year that the water table was highest, so the old ( decaying) lead cables were actually dangling in the water for decades.
> The wiring between the sockets hung down in long loops, and in some places there was a ' tide mark' on the wires from the times of the year that the water table was highest, so the old ( decaying) lead cables were actually dangling in the water for decades.
You're describing exactly the situation under my floor except at some point it's been switched to big loops of PVC twin and earth that trails through the flood along with the big unsecured (and now isolated) loops of gas plumbing. The old lead cable is clipped up neatly high and dry though presumably the rubber had perished and started smoking by the 80s when the clown rewired. The gas fires were gaffa-taped to the chimneys when we moved in and one was leaking gas. How it hadn't killed the previous owners one way or another I don't know. I'm still nervous when cutting out the lead wiring in case some knobber has left a length of it live somehow.
jk
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In reply to csambrook:
That's rubbish!!
Earlier on in the thread you said that 6mm cable had the capacity to take up to 46a. Now you're saying the mcb wont trip until there is possibly 150a of overcurrent. So what you're saying now is, that it is the cable that is the weak link in the circuit and not the trip.
Might as well not bother with the trip and just wire it straight though.
> As Hooo has said it takes a looong time to trip a 32A MCB at 39A. Quite possibly forever.
> A type B MCB, which is probably what's fitted, is specified to trip when the overload reaches a set level. Wait for it... between 3 and 5 times full load current. Bit of a shocker that isn't it, you might end up with 150A before the MCB trips!
That's rubbish!!
Earlier on in the thread you said that 6mm cable had the capacity to take up to 46a. Now you're saying the mcb wont trip until there is possibly 150a of overcurrent. So what you're saying now is, that it is the cable that is the weak link in the circuit and not the trip.
Might as well not bother with the trip and just wire it straight though.
1
In reply to arch:
Nope. That's not what he said.
He didn't say it could take up to 46A, he said it was rated up to 46A. Big difference.
Rated means that in certain circumstances it can be used to safely carry 46A. It will take a lot more before it melts or catches fire. It will happily take 150A for long enough to trip an MCB.
That's why MCBs are made with that time profile, they are designed to not trip during a brief overcurrent, because the cable they are protecting can take it.
> That's rubbish!!
> Earlier on in the thread you said that 6mm cable had the capacity to take up to 46a. Now you're saying the mcb wont trip until there is possibly 150a of overcurrent. So what you're saying now is, that it is the cable that is the weak link in the circuit and not the trip.
> Might as well not bother with the trip and just wire it straight though.
Nope. That's not what he said.
He didn't say it could take up to 46A, he said it was rated up to 46A. Big difference.
Rated means that in certain circumstances it can be used to safely carry 46A. It will take a lot more before it melts or catches fire. It will happily take 150A for long enough to trip an MCB.
That's why MCBs are made with that time profile, they are designed to not trip during a brief overcurrent, because the cable they are protecting can take it.
In reply to arch:
Jesus Christ, you call yourself and electrician and then ask this question?
Did you do a "real" apprenticeship or just the "quickie" route?
Anyone who's ever picked up a copy of the Wiring regulations in the last 20 years SHOULD be able to answer that question, never mind somebody that's SUPPOSED to be an electrician.
Have you never done the "Requirements Electrical Installations BS 7671: 2008" course?
> So why isn't the 32A MCB tripping then ??
Jesus Christ, you call yourself and electrician and then ask this question?
Did you do a "real" apprenticeship or just the "quickie" route?
Anyone who's ever picked up a copy of the Wiring regulations in the last 20 years SHOULD be able to answer that question, never mind somebody that's SUPPOSED to be an electrician.
Have you never done the "Requirements Electrical Installations BS 7671: 2008" course?
2
In reply to arch:
You are dangerous, mate.
To the OP if you rely on information from this type of "electrician" then you really need to visit a professional.
I haven't done the calculations or looked in the regs but it's looks like your shower is already underrated, for your safety and the safety of your family, spend a few quid and some time and do the job properly.
The regs are there for a reason and blokes telling you it'll be fine doesn't make it so.
> That's rubbish!!
> Earlier on in the thread you said that 6mm cable had the capacity to take up to 46a. Now you're saying the mcb wont trip until there is possibly 150a of overcurrent. So what you're saying now is, that it is the cable that is the weak link in the circuit and not the trip.
> Might as well not bother with the trip and just wire it straight though.
You are dangerous, mate.
To the OP if you rely on information from this type of "electrician" then you really need to visit a professional.
I haven't done the calculations or looked in the regs but it's looks like your shower is already underrated, for your safety and the safety of your family, spend a few quid and some time and do the job properly.
The regs are there for a reason and blokes telling you it'll be fine doesn't make it so.
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In reply to Hooo:
so mcb will not trip in time it takes to shower or quite possibly never [ it takes a looong time to trip a 32A MCB at 39A. Quite possibly forever.]
may be worth looking at the time current curve for type b,, as forever is a long time
and that pvc /pvc [[ will happily take 150A for long enough to trip an MCB.]]
somewhere i think that we have a contradiction
And
Might as well not bother with the trip and just wire it straight though.
yer this is also knows as BS; 3036
so mcb will not trip in time it takes to shower or quite possibly never [ it takes a looong time to trip a 32A MCB at 39A. Quite possibly forever.]
may be worth looking at the time current curve for type b,, as forever is a long time
and that pvc /pvc [[ will happily take 150A for long enough to trip an MCB.]]
somewhere i think that we have a contradiction
And
Might as well not bother with the trip and just wire it straight though.
yer this is also knows as BS; 3036
1
In reply to Name Changed 34:
When in doubt (nuisance tripping etc.), I use BS1202-1:2002 protective devices
When in doubt (nuisance tripping etc.), I use BS1202-1:2002 protective devices
1
In reply to csambrook:
need to understand that there are 2 separate elements that can trigger a trip in an mcb; thermal and magnetic. Most folk are referring to the mag settings of 3 to 5 In for a B curve. At these levels of current the mcb must trip within 0.1 seconds (to the mcb stds). It's commonly know as instantaneous trip. The thermal trip operates in a completely different way from In up until when the mag trip takes over. The more current the faster the trip. For example it will never trip at In, must trip within 60 minutes at 1.45In (56.55A) and will get faster as the current increases, until the instaneous trip takes over at 3 to 5 In. Hope that explains it clearly enough.
need to understand that there are 2 separate elements that can trigger a trip in an mcb; thermal and magnetic. Most folk are referring to the mag settings of 3 to 5 In for a B curve. At these levels of current the mcb must trip within 0.1 seconds (to the mcb stds). It's commonly know as instantaneous trip. The thermal trip operates in a completely different way from In up until when the mag trip takes over. The more current the faster the trip. For example it will never trip at In, must trip within 60 minutes at 1.45In (56.55A) and will get faster as the current increases, until the instaneous trip takes over at 3 to 5 In. Hope that explains it clearly enough.
3
In reply to DancingOnRock:
I posted a link to that earlier DOR, but there were others electrically qualified that said that the 6mm2 with the existing 9KW would be OK
( albeit it was against the manufacture's guidance)
http://www.mirashowers.co.uk/common/pdf/Miras-Guide-to-Electric-Showers.pdf
I'm keeping well out of the industry arguments, I'm not qualified, so I stick to the ,worst case end , of the regulations/ manufacturers guidelines.
MY options would have been , as you point out, to either install a new lower ( under 8KW) rated shower to match the 6mm2 cable, or spend less money to upgrade and replace everything from the shower back to the consumer unit, cheaper yes but more hassle .
( not sure if JLS ever answered me on whether he already had the other guideline recommendations , RCD, Bonding , MCB rating, etc., I need to read back)
> The Mira instruction book says 10mm2 for all showers above 8kW.
I posted a link to that earlier DOR, but there were others electrically qualified that said that the 6mm2 with the existing 9KW would be OK
( albeit it was against the manufacture's guidance)
http://www.mirashowers.co.uk/common/pdf/Miras-Guide-to-Electric-Showers.pdf
I'm keeping well out of the industry arguments, I'm not qualified, so I stick to the ,worst case end , of the regulations/ manufacturers guidelines.
MY options would have been , as you point out, to either install a new lower ( under 8KW) rated shower to match the 6mm2 cable, or spend less money to upgrade and replace everything from the shower back to the consumer unit, cheaper yes but more hassle .
( not sure if JLS ever answered me on whether he already had the other guideline recommendations , RCD, Bonding , MCB rating, etc., I need to read back)
In reply to Jim C:
A 6mil cable, clipped direct along its entire length, with a 40A OCPD complies for a 9kW shower.
Next!
A 6mil cable, clipped direct along its entire length, with a 40A OCPD complies for a 9kW shower.
Next!
In reply to Lusk:
Is that what the OP has?
Edit , that.
> A 6mil cable, clipped direct along its entire length, with a 40A OCPD complies for a 9kW shower.
> Next!
Is that what the OP has?
Edit , that.
Post edited at 19:53
In reply to krikoman:
Years ago when I ventured out into the real world and had to deal with regular domestic and site electricians, I was shocked to discover that nearly all of them had no understanding of fundamental electrical concepts or how anything worked.
Then an ex-electrician who did understand explained to me: An electricians job is 90% cutting holes and pulling cables, and the other 10% is covered by following the regulations. There is no need for any deeper understanding, just learn the rules and stick to them and your installations will work and be safe.
Obviously the regs have to err on the safe side, so there is plenty of stuff that will be fine in practice but wouldn't comply. Like the OPs shower for instance.
If you want to know if something complies with regulations, ask an electrician. If you want to know if something that doesn't meet regs will nevertheless work and be safe, you need to ask an electrical engineer.
Years ago when I ventured out into the real world and had to deal with regular domestic and site electricians, I was shocked to discover that nearly all of them had no understanding of fundamental electrical concepts or how anything worked.
Then an ex-electrician who did understand explained to me: An electricians job is 90% cutting holes and pulling cables, and the other 10% is covered by following the regulations. There is no need for any deeper understanding, just learn the rules and stick to them and your installations will work and be safe.
Obviously the regs have to err on the safe side, so there is plenty of stuff that will be fine in practice but wouldn't comply. Like the OPs shower for instance.
If you want to know if something complies with regulations, ask an electrician. If you want to know if something that doesn't meet regs will nevertheless work and be safe, you need to ask an electrical engineer.
3
1
In reply to JLS:
Yikes! This thread is still live!
I almost feel like just buying a thermostatic shower and binning the electric one.
As a bit background I bought the house just under 2 years ago. It's twelve years old, but I've come to realise the last owner was a bit of a cowboy with his DIY. I fear the current shower set-up may have been put in by the previous owner so I had my doubts it would be to regs.
Anyway I'm re-doing the whole bathroom. Currently the wall the shower was on doesn't even have plaster board so cable access is easy and I might as well just put in the 10mm2 cable.
I'm moving the pull cord because it's currently positioned within reach of the shower!
I'll probably get an electrician (an old neighbour), to make the connection final connection to the consumer unit and give my work the once over.
The Scottish system of home reports rather than proper surveys means very often people are buying houses containing all sorts of nightmares but that's another thread...
Thanks all for your intrest.
Yikes! This thread is still live!
I almost feel like just buying a thermostatic shower and binning the electric one.
As a bit background I bought the house just under 2 years ago. It's twelve years old, but I've come to realise the last owner was a bit of a cowboy with his DIY. I fear the current shower set-up may have been put in by the previous owner so I had my doubts it would be to regs.
Anyway I'm re-doing the whole bathroom. Currently the wall the shower was on doesn't even have plaster board so cable access is easy and I might as well just put in the 10mm2 cable.
I'm moving the pull cord because it's currently positioned within reach of the shower!
I'll probably get an electrician (an old neighbour), to make the connection final connection to the consumer unit and give my work the once over.
The Scottish system of home reports rather than proper surveys means very often people are buying houses containing all sorts of nightmares but that's another thread...
Thanks all for your intrest.
In reply to JLS:
Is now a good time to suggest something different? Fit a lower power shower and a heat recovery unit to pre-heat the incoming water from the waste. Eco friendly and no need to upgrade the cable.... Cost is about £800 if I remember right....
> I almost feel like just buying a thermostatic shower and binning the electric one.
Is now a good time to suggest something different? Fit a lower power shower and a heat recovery unit to pre-heat the incoming water from the waste. Eco friendly and no need to upgrade the cable.... Cost is about £800 if I remember right....
In reply to wintertree:
Hold on, earlier we worked out he could upgrade the wiring , MCB and pull switch for about 80 quid. Even if he got an electrician in to do the work, it would be nowhere near that cost. How much will he save with the low power shower to recover that outlay and over what period?
( ignoring the Eco friendly warm feeling)
> Is now a good time to suggest something different? Fit a lower power shower and a heat recovery unit to pre-heat the incoming water from the waste. Eco friendly and no need to upgrade the cable.... Cost is about £800 if I remember right....
Hold on, earlier we worked out he could upgrade the wiring , MCB and pull switch for about 80 quid. Even if he got an electrician in to do the work, it would be nowhere near that cost. How much will he save with the low power shower to recover that outlay and over what period?
( ignoring the Eco friendly warm feeling)
In reply to Jim C:
Yeah, £800 would be a very significant increase in budget when I've already committed a fair bit into the rest of the project. The other thing is that, this only a second shower which won't see regular use. Happy to pay to make to make it safe but an upgrade isn't really required.
Yeah, £800 would be a very significant increase in budget when I've already committed a fair bit into the rest of the project. The other thing is that, this only a second shower which won't see regular use. Happy to pay to make to make it safe but an upgrade isn't really required.
In reply to Hooo:
That's a plate of egg and chip,
An electricians job is not cutting holes that what a electricians laborer is for
Ask electrical engineer.
A I had friend who read electrical engineering at Emanuel would not have had a clue how to size a cable to a shower or apply correction factor's to it.
edit the italics have inverted [no pun]
That's a plate of egg and chip,
An electricians job is not cutting holes that what a electricians laborer is for
> just learn the rules and stick to them Dont know if you have ever seen or followed the A,B / part 1, 2 of electrical instillation but historically it has had provided a solid grounding [no pun] in the fundamentals.
Ask electrical engineer.
A I had friend who read electrical engineering at Emanuel would not have had a clue how to size a cable to a shower or apply correction factor's to it.
edit the italics have inverted [no pun]
Post edited at 12:35
In reply to David Bennett:
Well put, so well put I could see the graph rising as I read
you should write text books
Well put, so well put I could see the graph rising as I read
you should write text books
In reply to Name Changed 34:
It's a huge field.
A domestic electrician would be lost in an industrial setting.
> That's a plate of egg and chip,
> An electricians job is not cutting holes that what a electricians laborer is for
> Ask electrical engineer.
> A I had friend who read electrical engineering at Emanuel would not have had a clue how to size a cable to a shower or apply correction factor's to it.
> edit the italics have inverted [no pun]
It's a huge field.
A domestic electrician would be lost in an industrial setting.
In reply to Name Changed 34:
It's a huge field.
A domestic electrician would be lost in an industrial setting.
Even some domestic electricians are lost in a domestic setting.
The guy who wired and tested my house refused to replace an MCB that was nuisance tripping even though every test he was doing indicated it was faulty.
Wouldn't even swap it over with another one in the board to prove me wrong.
> That's a plate of egg and chip,
> An electricians job is not cutting holes that what a electricians laborer is for
> Ask electrical engineer.
> A I had friend who read electrical engineering at Emanuel would not have had a clue how to size a cable to a shower or apply correction factor's to it.
> edit the italics have inverted [no pun]
It's a huge field.
A domestic electrician would be lost in an industrial setting.
Even some domestic electricians are lost in a domestic setting.
The guy who wired and tested my house refused to replace an MCB that was nuisance tripping even though every test he was doing indicated it was faulty.
Wouldn't even swap it over with another one in the board to prove me wrong.
In reply to Lusk:
But it's not clipped direct along it's length "The cable is clipped to walls (garage, bedroom cupboard) over about half its length, the other half is running against loft insulation."
Against doesn't say whether it's under or on top or how much insulation there is if it's under.
Next!!
> A 6mil cable, clipped direct along its entire length, with a 40A OCPD complies for a 9kW shower.
> Next!
But it's not clipped direct along it's length "The cable is clipped to walls (garage, bedroom cupboard) over about half its length, the other half is running against loft insulation."
Against doesn't say whether it's under or on top or how much insulation there is if it's under.
Next!!
1
In reply to DancingOnRock:
for clarity what is a domestic electrician. Are you referring to a part P Joey
> Even some domestic electricians are lost in a domestic setting.
for clarity what is a domestic electrician. Are you referring to a part P Joey
In reply to Hooo:
What about the stuff that doesn't comply and isn't safe because the bloke that installed it doesn't understand fusing or trip curves?
It's OK saying the cable is OK and the fuse is OK but what about de-rating for the insulation?
Coming on here say it'll be OK is nothing more than reckless without knowing how it's installed at present. Saying you're a 'leccy to prove what you've just said just make you look stupid, stupid and dangerous.
It's the difference between possibly OK, probably OK, and definitely OK. If someone said this about the brakes on your car as you were setting off with you family on holiday, which would you choose?
PS I'm an industrial Electrical Engineer with roughly 30 years experience.
To the OP, you've chosen the best option. Well done.
> Then an ex-electrician who did understand explained to me: An electricians job is 90% cutting holes and pulling cables, and the other 10% is covered by following the regulations. There is no need for any deeper understanding, just learn the rules and stick to them and your installations will work and be safe.
> Obviously the regs have to err on the safe side, so there is plenty of stuff that will be fine in practice but wouldn't comply. Like the OPs shower for instance.
What about the stuff that doesn't comply and isn't safe because the bloke that installed it doesn't understand fusing or trip curves?
> If you want to know if something complies with regulations, ask an electrician. If you want to know if something that doesn't meet regs will nevertheless work and be safe, you need to ask an electrical engineer.
It's OK saying the cable is OK and the fuse is OK but what about de-rating for the insulation?
Coming on here say it'll be OK is nothing more than reckless without knowing how it's installed at present. Saying you're a 'leccy to prove what you've just said just make you look stupid, stupid and dangerous.
It's the difference between possibly OK, probably OK, and definitely OK. If someone said this about the brakes on your car as you were setting off with you family on holiday, which would you choose?
PS I'm an industrial Electrical Engineer with roughly 30 years experience.
To the OP, you've chosen the best option. Well done.
1
In reply to Name Changed 34:
Someone who works day in day out in a domestic situation. Lighting, sockets, 230v single phase consumer units etc.
Some of these guys really know their stuff. Some haven't got a clue.
Actually I was misremembering. It was an RCBO. I had a very long 'discussion' with him trying to explain how it worked.
> for clarity what is a domestic electrician. Are you referring to a part P Joey
Someone who works day in day out in a domestic situation. Lighting, sockets, 230v single phase consumer units etc.
Some of these guys really know their stuff. Some haven't got a clue.
Actually I was misremembering. It was an RCBO. I had a very long 'discussion' with him trying to explain how it worked.
In reply to Name Changed 34:
You have got to be joking. An electrical engineer who couldn't do that. I don't believe you. He might not know the figures off the top of his head, but I'm sure he could work it out.
> That's a plate of egg and chip,
> A I had friend who read electrical engineering at Emanuel would not have had a clue how to size a cable to a shower or apply correction factor's to it.
You have got to be joking. An electrical engineer who couldn't do that. I don't believe you. He might not know the figures off the top of his head, but I'm sure he could work it out.
In reply to krikoman:
I never claimed to be a 'leccy or said it would be OK. I was just pointing out that it was no surprise that an electrician didn't understand why a 39A shower wouldn't trip a 32A breaker.
I never claimed to be a 'leccy or said it would be OK. I was just pointing out that it was no surprise that an electrician didn't understand why a 39A shower wouldn't trip a 32A breaker.
1
In reply to Hooo:
[[I don't believe you. He might not know the figures off the top of his head, but I'm sure he could work it out.]]
well yes of course he could work it out, if he knew what was involved in 7671, just as any electrician [not technician aka part P] can.. But.......... if he knew what was involved, and he did not .......... why would he have a knowledge of 7671?
that,s is why yours [[ If you want to know if something that doesn't meet regs will nevertheless work and be safe, you need to ask an electrical engineer.][ is egg and chips
[[I don't believe you. He might not know the figures off the top of his head, but I'm sure he could work it out.]]
well yes of course he could work it out, if he knew what was involved in 7671, just as any electrician [not technician aka part P] can.. But.......... if he knew what was involved, and he did not .......... why would he have a knowledge of 7671?
that,s is why yours [[ If you want to know if something that doesn't meet regs will nevertheless work and be safe, you need to ask an electrical engineer.][ is egg and chips
1
In reply to krikoman:
Is that snidey comment aimed at me ??
I've been looking at some your posts on your profile and you're quite free with the snidey comments and put downs. Got quite angry on your "Food not bombs" thread didn't we. You've not got an anger management problem have you ??
If you read back on this topic, I wasn't the only one to say the OP would be fine to extend his shower circuit by a whopping 3m, so wind your neck in.
.......Oh, and one other thing.
"You are dangerous, mate"
Well I can tell you one thing. I ain't your fuc*ing mate.
>
>
> Coming on here say it'll be OK is nothing more than reckless without knowing how it's installed at present. Saying you're a 'leccy to prove what you've just said just make you look stupid, stupid and dangerous.
>
>
>
Is that snidey comment aimed at me ??
I've been looking at some your posts on your profile and you're quite free with the snidey comments and put downs. Got quite angry on your "Food not bombs" thread didn't we. You've not got an anger management problem have you ??
If you read back on this topic, I wasn't the only one to say the OP would be fine to extend his shower circuit by a whopping 3m, so wind your neck in.
.......Oh, and one other thing.
"You are dangerous, mate"
Well I can tell you one thing. I ain't your fuc*ing mate.
2
2
In reply to krikoman:
OK big boy, what Installation/Reference Method would you attribute to Flat T&E laying on top of loft insulation?
edit: and open to the surrounding air.
> PS I'm an industrial Electrical Engineer with roughly 30 years experience.
OK big boy, what Installation/Reference Method would you attribute to Flat T&E laying on top of loft insulation?
edit: and open to the surrounding air.
Post edited at 19:56
1
1
In reply to JLS:
OMG!
What an embarrassing thread!
and like Kaiser Solce..... I'm a sparks too.
I wish I'd thought of it as a troll!
OMG!
What an embarrassing thread!
and like Kaiser Solce..... I'm a sparks too.
I wish I'd thought of it as a troll!
1
In reply to arch:
Ha ha very funny.
I don't see how you get angry from my posts, perhaps it's your aggression blinding you!
He's some of what you've written.
So why isn't the 32A MCB tripping then ??
That's rubbish!!
Earlier on in the thread you said that 6mm cable had the capacity to take up to 46a. Now you're saying the mcb wont trip until there is possibly 150a of overcurrent. So what you're saying now is, that it is the cable that is the weak link in the circuit and not the trip.
Might as well not bother with the trip and just wire it straight though.
As I completed my C&G 236 Electrical Installation part 1 and 2 Apprenticeship in 1985 at Loughborough college and have worked In the Electrical industry ever since, i'd say I know what i'm talking about.
OK, now here's the important bit, a 32A type B breaker will allow a current of approximately 45A for at least 10,000 seconds (that's nearly 3 hours) it will also allow a current of 105A for 10 seconds and 160A for up to 5s.
http://wiki.diyfaq.org.uk/images/d/d4/Curve-MCBTypeB.png
A type C will allow more current in 10 seconds and a type D 110 A for 10 seconds (and 640A for up to 5 seconds), while the maximum continuous current stays the same at 45A
As you were unaware of these facts, indeed thought it laughable that a 32A trip could carry more current, how confident are you in telling him it'll be alright?
Especially when nobody asked any questions about the routing of the cable and if any of it was covered by insulation, with only 100mm of the cable covered and you're down to 80% capacity!!
Oh! and I don't think I'd like you as a mate, so we both happy with that situation.
Ha ha very funny.
I don't see how you get angry from my posts, perhaps it's your aggression blinding you!
He's some of what you've written.
So why isn't the 32A MCB tripping then ??
> As Hooo has said it takes a looong time to trip a 32A MCB at 39A. Quite possibly forever.
> A type B MCB, which is probably what's fitted, is specified to trip when the overload reaches a set level. Wait for it... between 3 and 5 times full load current. Bit of a shocker that isn't it, you might end up with 150A before the MCB trips!
That's rubbish!!
Earlier on in the thread you said that 6mm cable had the capacity to take up to 46a. Now you're saying the mcb wont trip until there is possibly 150a of overcurrent. So what you're saying now is, that it is the cable that is the weak link in the circuit and not the trip.
Might as well not bother with the trip and just wire it straight though.
As I completed my C&G 236 Electrical Installation part 1 and 2 Apprenticeship in 1985 at Loughborough college and have worked In the Electrical industry ever since, i'd say I know what i'm talking about.
OK, now here's the important bit, a 32A type B breaker will allow a current of approximately 45A for at least 10,000 seconds (that's nearly 3 hours) it will also allow a current of 105A for 10 seconds and 160A for up to 5s.
http://wiki.diyfaq.org.uk/images/d/d4/Curve-MCBTypeB.png
A type C will allow more current in 10 seconds and a type D 110 A for 10 seconds (and 640A for up to 5 seconds), while the maximum continuous current stays the same at 45A
As you were unaware of these facts, indeed thought it laughable that a 32A trip could carry more current, how confident are you in telling him it'll be alright?
Especially when nobody asked any questions about the routing of the cable and if any of it was covered by insulation, with only 100mm of the cable covered and you're down to 80% capacity!!
Oh! and I don't think I'd like you as a mate, so we both happy with that situation.
Post edited at 20:42
In reply to Hooo:
No I was disagreeing with you, you were correct on both counts. Top marks
> I never claimed to be a 'leccy or said it would be OK. I was just pointing out that it was no surprise that an electrician didn't understand why a 39A shower wouldn't trip a 32A breaker.
No I was disagreeing with you, you were correct on both counts. Top marks
In reply to Lusk:
I wasn't showing off, it might just be important for the OP to help make a decision, after all Arch has been to college and completed parts 1 and 2. I didn't want to appear as some troll dissing Arch for the sake of it.
I'd used clipped direct but then, if you have 100mm and the cable has to run through it then you'd need to de-rate it. also, in our loft temperatures in the summer get way above 40 deg. C so I'd de-rate it again for that.
The OPs cable while probably adequate (the way it was described), but was possibly borderline for any changes in environment or for future upgrade, of either insulation in the loft or higher power shower. I looked at it from my perspective, I'm going in the loft to extend a bit of cable on a possibly borderline installation. For what it costs extra in time and money, you might as well start again and have some spare capacity. It's that simple.
My issue wasn't with the advice, but they way it was justified, without having all the facts.
> OK big boy, what Installation/Reference Method would you attribute to Flat T&E laying on top of loft insulation?
> edit: and open to the surrounding air.
I wasn't showing off, it might just be important for the OP to help make a decision, after all Arch has been to college and completed parts 1 and 2. I didn't want to appear as some troll dissing Arch for the sake of it.
I'd used clipped direct but then, if you have 100mm and the cable has to run through it then you'd need to de-rate it. also, in our loft temperatures in the summer get way above 40 deg. C so I'd de-rate it again for that.
The OPs cable while probably adequate (the way it was described), but was possibly borderline for any changes in environment or for future upgrade, of either insulation in the loft or higher power shower. I looked at it from my perspective, I'm going in the loft to extend a bit of cable on a possibly borderline installation. For what it costs extra in time and money, you might as well start again and have some spare capacity. It's that simple.
My issue wasn't with the advice, but they way it was justified, without having all the facts.
In reply to krikoman:
Yes I misenterpreted the tripping capabilities of a miniature circuit breaker. Sometimes, shit happens.
But. You don't know me or know what I do for a living. Yet you've made the assumption I'm "Stupid" and "Dangerous" from a few posts on an internet forum. I doubt very much you would say these words to my face, so why do you feel its OK to say them from behind your keyboard ??
.......And judging by lots of your other posts on this forum, you also feel it is acceptable to say similar things to others as well.
Yes I misenterpreted the tripping capabilities of a miniature circuit breaker. Sometimes, shit happens.
But. You don't know me or know what I do for a living. Yet you've made the assumption I'm "Stupid" and "Dangerous" from a few posts on an internet forum. I doubt very much you would say these words to my face, so why do you feel its OK to say them from behind your keyboard ??
.......And judging by lots of your other posts on this forum, you also feel it is acceptable to say similar things to others as well.
In reply to arch:
Everything I say here, I'd say face to face, and let's be honest "that's rubbish" isn't any better response than saying someone's stupid, especially what it's so blatantly not rubbish, but fact!
> Yes I misenterpreted the tripping capabilities of a miniature circuit breaker. Sometimes, shit happens.
> But. You don't know me or know what I do for a living. Yet you've made the assumption I'm "Stupid" and "Dangerous" from a few posts on an internet forum. I doubt very much you would say these words to my face, so why do you feel its OK to say them from behind your keyboard ??
Everything I say here, I'd say face to face, and let's be honest "that's rubbish" isn't any better response than saying someone's stupid, especially what it's so blatantly not rubbish, but fact!
In reply to JLS:
Hey everyone, what type of cabling would I need to run from the consumer unit through the loft under standard insulation and down to the room with my computer in it, in order to power an industrial popcorn maker? Thanks.
Hey everyone, what type of cabling would I need to run from the consumer unit through the loft under standard insulation and down to the room with my computer in it, in order to power an industrial popcorn maker? Thanks.
7
In reply to wintertree:
Can you get WRAS approved waste heat exchangers? Waste heat recovery is a great idea but the implementation is rather hampered by regulations. £800 is crazy money, the payback period will be decades before you consider any extra maintenance it might need. I was sorely tempted to make my own when I refitted my bathroom but in the end it was too much trouble.
jk
> Is now a good time to suggest something different? Fit a lower power shower and a heat recovery unit to pre-heat the incoming water from the waste. Eco friendly and no need to upgrade the cable.... Cost is about £800 if I remember right....
Can you get WRAS approved waste heat exchangers? Waste heat recovery is a great idea but the implementation is rather hampered by regulations. £800 is crazy money, the payback period will be decades before you consider any extra maintenance it might need. I was sorely tempted to make my own when I refitted my bathroom but in the end it was too much trouble.
jk
In reply to Dervish:
Maybe the diesel estate model.
jk
> Will that work on a Skodav Octavia?
Maybe the diesel estate model.
jk
In reply to jkarran:
Sorry jk. Hamfisted phone use deleted my original question.
But thanks, that's good news.
Will it also work on the Yeti?
Sorry jk. Hamfisted phone use deleted my original question.
But thanks, that's good news.
Will it also work on the Yeti?
Post edited at 09:18
In reply to jkarran:
Okay, I was out by a factor of ~ 2 on the price, or it's dropped since I last looked. The Recoh-vert is WRAS approved and costs £470. It's basically a coaxial drain pipe and cold water feed with some barriers to increase protection against cross contamination of the inflow. My interest was in increasing the quantity of hot water I could get out of an electric shower rather than saving energy... We use a shower so rarely thought that it just didn't seem worth it.
http://shower-save.com/products/recoh-vert.html
> Can you get WRAS approved waste heat exchangers? Waste heat recovery is a great idea but the implementation is rather hampered by regulations. £800 is crazy money, the payback period will be decades before you consider any extra maintenance it might need. I was sorely tempted to make my own when I refitted my bathroom but in the end it was too much trouble.
Okay, I was out by a factor of ~ 2 on the price, or it's dropped since I last looked. The Recoh-vert is WRAS approved and costs £470. It's basically a coaxial drain pipe and cold water feed with some barriers to increase protection against cross contamination of the inflow. My interest was in increasing the quantity of hot water I could get out of an electric shower rather than saving energy... We use a shower so rarely thought that it just didn't seem worth it.
http://shower-save.com/products/recoh-vert.html
1
In reply to EddInaBox:
You could wire it all in fuse wire, it's really thin and carries a lot of current. it's a piece of piss to install too.
> Hey everyone, what type of cabling would I need to run from the consumer unit through the loft under standard insulation and down to the room with my computer in it, in order to power an industrial popcorn maker? Thanks.
You could wire it all in fuse wire, it's really thin and carries a lot of current. it's a piece of piss to install too.
Post edited at 11:14
In reply to wintertree:
Looks easy enough to make, I'd be a bit concerned about the drain diameter and my daughters hair, which has some sort of magical cling-on properties.
Looks easy enough to make, I'd be a bit concerned about the drain diameter and my daughters hair, which has some sort of magical cling-on properties.
In reply to krikoman:
That's the clever bit - the waste water runs in a thin film down the inner face of the large bore central cylinder, so it isn't prone to clogging or blockage, and is copper so you can use all manner of nasty cleaning chemicals on it. I also suspect that dispersing the flow into a surface contacting film is the hard part to get right when making it yourself.
> Looks easy enough to make, I'd be a bit concerned about the drain diameter and my daughters hair, which has some sort of magical cling-on properties.
That's the clever bit - the waste water runs in a thin film down the inner face of the large bore central cylinder, so it isn't prone to clogging or blockage, and is copper so you can use all manner of nasty cleaning chemicals on it. I also suspect that dispersing the flow into a surface contacting film is the hard part to get right when making it yourself.
In reply to wintertree:
Water is pretty clingy, I suspect you'd have more trouble trying to prevent it from forming a film. Shame about the price!
jk
> I also suspect that dispersing the flow into a surface contacting film is the hard part to get right when making it yourself.
Water is pretty clingy, I suspect you'd have more trouble trying to prevent it from forming a film. Shame about the price!
jk
In reply to jkarran:
Perhaps. Shower waste is often detergent rich which modifies surface tension a lot. Sounds like a simple home experiment however!
Indeed. I imagine they need to get away from copper to fix that.
> Water is pretty clingy, I suspect you'd have more trouble trying to prevent it from forming a film.
Perhaps. Shower waste is often detergent rich which modifies surface tension a lot. Sounds like a simple home experiment however!
> Shame about the price!
Indeed. I imagine they need to get away from copper to fix that.
In reply to JLS:
Ok, so perhaps in view of the thread above I shouldn't ask but...
I'm now the proud owner of 17m of 10mm2 T+E cable for my 9kW shower.
I was thinking I needed a 45A mcb but Crabtree only seem to offer 40A or 50A.
Am I correct in assuming that I should go for the 50A?
https://www.tlc-direct.co.uk/Products/CB61slashB50.html
Won't the current 32A mbc offer more protection to the cable than a higher rated mcb, so why change it, if the shower doesn't trip it just now?
The currently the consumer unit "appears" to have the old shower 32A mbc wired to a Crabtree RCCD along with the two breakers for the upstairs and downstairs socket circuits.
How likely is it that a straight swap of the shower mbc, 50A for 32A won't cause any problems with the consumer unit RCCD arrangement?
With the cable upgrade to 10mm do I still need to be concerned about the proximity of the loft insulation? There is perhaps 3m length where the cable goes under loft flooring as so is quite tightly surrounded with the insulation.
Edit: Re: why change the 32A mbc. Have I got it right that it currently works only because of the time curve mention above and if I did have long full heat showers it would eventually trip?
Ok, so perhaps in view of the thread above I shouldn't ask but...
I'm now the proud owner of 17m of 10mm2 T+E cable for my 9kW shower.
I was thinking I needed a 45A mcb but Crabtree only seem to offer 40A or 50A.
Am I correct in assuming that I should go for the 50A?
https://www.tlc-direct.co.uk/Products/CB61slashB50.html
Won't the current 32A mbc offer more protection to the cable than a higher rated mcb, so why change it, if the shower doesn't trip it just now?
The currently the consumer unit "appears" to have the old shower 32A mbc wired to a Crabtree RCCD along with the two breakers for the upstairs and downstairs socket circuits.
How likely is it that a straight swap of the shower mbc, 50A for 32A won't cause any problems with the consumer unit RCCD arrangement?
With the cable upgrade to 10mm do I still need to be concerned about the proximity of the loft insulation? There is perhaps 3m length where the cable goes under loft flooring as so is quite tightly surrounded with the insulation.
Edit: Re: why change the 32A mbc. Have I got it right that it currently works only because of the time curve mention above and if I did have long full heat showers it would eventually trip?
Post edited at 09:22
In reply to JLS:
Your logic seems sound to me regarding keeping the current 32A mcb, if it blows then you can always replace it.
Your logic seems sound to me regarding keeping the current 32A mcb, if it blows then you can always replace it.
1
In reply to JLS:
37A is not all that much over 32A in the scheme of things. Perhaps there's a bit of leeway in the specs and/or manufacturing tolerances there too: maybe your shower is a bit under 9kW and your MCB a bit over 32A. Perhaps your voltage might also be a bit lower than the shower is specced for - if it's 9kW at 240V it'll only be about 8.3kW at 230V. (And drawing a couple of amps less current.)
I don't see any reason not to leave the existing MCB in and replace it only if you have to but NB: I am not an electrician and have absolutely no idea what I'm wibbling on about! ;O)
> Edit: Re: why change the 32A mbc. Have I got it right that it currently works only because of the time curve mention above and if I did have long full heat showers it would eventually trip?
37A is not all that much over 32A in the scheme of things. Perhaps there's a bit of leeway in the specs and/or manufacturing tolerances there too: maybe your shower is a bit under 9kW and your MCB a bit over 32A. Perhaps your voltage might also be a bit lower than the shower is specced for - if it's 9kW at 240V it'll only be about 8.3kW at 230V. (And drawing a couple of amps less current.)
I don't see any reason not to leave the existing MCB in and replace it only if you have to but NB: I am not an electrician and have absolutely no idea what I'm wibbling on about! ;O)
In reply to deepsoup:
- if it's 9kW at 240V it'll only be about 8.3kW at 230V. (And drawing a couple of amps less current.)
>9000/220=40.9
9000/250=36.0
- if it's 9kW at 240V it'll only be about 8.3kW at 230V. (And drawing a couple of amps less current.)
>9000/220=40.9
9000/250=36.0
1
In reply to Name Changed 34:
Doesn't work like that.
The rating on the side of the box is just its nominal power at a certain nominal voltage but the power is not fixed, it varies with the voltage. If there were a load of electronics in there regulating the output power you might be right, but there isn't; the heating element is essentially just a big water-cooled resistor.
If it's 9kW at 240V, 9000/240=37.5A and the resistance is about 6.4 Ohm.
250V -> 9.7kW ish, drawing 39A
230V -> 8.3kW ish, drawing 36A
(This is neglecting any change in the resistance with operating temperature, which I don't think is significant but could be I suppose.)
Doesn't work like that.
The rating on the side of the box is just its nominal power at a certain nominal voltage but the power is not fixed, it varies with the voltage. If there were a load of electronics in there regulating the output power you might be right, but there isn't; the heating element is essentially just a big water-cooled resistor.
If it's 9kW at 240V, 9000/240=37.5A and the resistance is about 6.4 Ohm.
250V -> 9.7kW ish, drawing 39A
230V -> 8.3kW ish, drawing 36A
(This is neglecting any change in the resistance with operating temperature, which I don't think is significant but could be I suppose.)
Post edited at 11:36
In reply to Name Changed 34:
But P is a function of the voltage and the current allowed to flow because of the resistance in the device so if the shower is specified as being 9 kW with a 250v supply if the voltage is dropped to 230 v then the current drops.
> >9000/220=40.9
> 9000/250=36.0
But P is a function of the voltage and the current allowed to flow because of the resistance in the device so if the shower is specified as being 9 kW with a 250v supply if the voltage is dropped to 230 v then the current drops.
In reply to JLS:
Now you've blown it!! (Pun intended)
Don't worry though. It wont be long before some know-it-all will be here to inform you that because Crabtree don't supply a 45a trip, you'll now have to change your whole consumer unit to one that does................
> Ok, so perhaps in view of the thread above I shouldn't ask but...
> I'm now the proud owner of 17m of 10mm2 T+E cable for my 9kW shower.
> I was thinking I needed a 45A mcb but Crabtree only seem to offer 40A or 50A.
Now you've blown it!! (Pun intended)
Don't worry though. It wont be long before some know-it-all will be here to inform you that because Crabtree don't supply a 45a trip, you'll now have to change your whole consumer unit to one that does................
Post edited at 09:23
2
In reply to JLS:
Hope that helps, please don't ask any more questions
P.S. ?You don't need to change the whole consumer unit, that would be mental!!
> Ok, so perhaps in view of the thread above I shouldn't ask but...
ha ha, I don't blame you!> I'm now the proud owner of 17m of 10mm2 T+E cable for my 9kW shower.
Nice one.> I was thinking I needed a 45A mcb but Crabtree only seem to offer 40A or 50A.
Leave the 32A in for now, if it starts tripping go for the 40A> Am I correct in assuming that I should go for the 50A?
No need for this.> Won't the current 32A mbc offer more protection to the cable than a higher rated mcb, so why change it, if the shower doesn't trip it just now?
Yes .> The currently the consumer unit "appears" to have the old shower 32A mbc wired to a Crabtree RCCD along with the two breakers for the upstairs and downstairs socket circuits.
This sound alright.> How likely is it that a straight swap of the shower mbc, 50A for 32A won't cause any problems with the consumer unit RCCD arrangement?
Shouldn't make any difference as the RCCD is independent of the circuit breaker size.> With the cable upgrade to 10mm do I still need to be concerned about the proximity of the loft insulation? There is perhaps 3m length where the cable goes under loft flooring as so is quite tightly surrounded with the insulation.
My regs are on site but off hand you should be good for around 42-45A and your system is only 39A.> Edit: Re: why change the 32A mbc. Have I got it right that it currently works only because of the time curve mention above and if I did have long full heat showers it would eventually trip?
Yes don't yet do it is you have trouble, you've got slightly more voltage as with 10mm you've got less voltage drop1.3% as opposed to about 4%. So if you were marginal before you might get some tripping, but the 40A trip will cure that.Hope that helps, please don't ask any more questions
P.S. ?You don't need to change the whole consumer unit, that would be mental!!
Post edited at 12:26
In reply to krikoman:
P.S. ?You don't need to change the whole consumer unit, that would be mental!!
are we sure about this?
OP states
32A mbc wired to a Crabtree RCCD along with the two breakers for the upstairs and downstairs socket circuits.
And
that is not sounding like a split lode box ------------- as is a requirement for 17th So may sound ok but is it?
From the AEEU book as thats all i have to hand
''Volt droop
one of the most stringent constraints affecting cable choice of conductor size is that concerning volt drop''
it states 4% max and a given formula of cable length 9M design current [assuming] 41Amp mV/A/m over 1000
how did we get about 4%?
P.S. ?You don't need to change the whole consumer unit, that would be mental!!
are we sure about this?
OP states
32A mbc wired to a Crabtree RCCD along with the two breakers for the upstairs and downstairs socket circuits.
And
that is not sounding like a split lode box ------------- as is a requirement for 17th So may sound ok but is it?
From the AEEU book as thats all i have to hand
''Volt droop
one of the most stringent constraints affecting cable choice of conductor size is that concerning volt drop''
it states 4% max and a given formula of cable length 9M design current [assuming] 41Amp mV/A/m over 1000
how did we get about 4%?
Post edited at 14:04
Not Home for another 3 weeks, but when home I shall use this as a refresher, and pull Guideens notes, reg's and do the Full FULL calculations, and justification----------------------- now that having fun!
In reply to krikoman:
.......But it won't will it. Remember ??
Thu 25 Feb 20:41
"OK, now here's the important bit, a 32A type B breaker will allow a current of approximately 45A for at least 10,000 seconds (that's nearly 3 hours)"
> Leave the 32A in for now, if it starts tripping go for the 40A
.......But it won't will it. Remember ??
Thu 25 Feb 20:41
"OK, now here's the important bit, a 32A type B breaker will allow a current of approximately 45A for at least 10,000 seconds (that's nearly 3 hours)"
In reply to krikoman:
I feel some what reassured. Thanks.
Probably be a while before I actually get around to running the cable down to the consumer unit.
Lots of more pressing work to be done.
How's your plumbing knowledge?
I feel some what reassured. Thanks.
Probably be a while before I actually get around to running the cable down to the consumer unit.
Lots of more pressing work to be done.
How's your plumbing knowledge?
In reply to JLS:
My plumbing was mainly industrial though and steel rather than copper. I once fitted a bathroom suite for £30!! It cost me more for tools, which is when I made my mind up never to work in people's houses, unless I couldn't do anything else.
> I feel some what reassured. Thanks.
> Probably be a while before I actually get around to running the cable down to the consumer unit.
> Lots of more pressing work to be done.
> How's your plumbing knowledge?
Ha ha, I actually served my apprenticeship as a plumber / welder did an ONC in that, then an HNC in Mechanical and Production Engineering then HNC electrical engineering then a B. Eng in Mechancial and Electrical Engineering ( This was where I parted company with the firm so never got to finish it sadly). The company I worked for, would let you carry on at college (day release and night classes) as long as you kept passing exams. They paid and there were no clauses about leaving and having to pay costs back. It's a pity there aren't more companies like that now. It was great and I didn't make my mind up on what I wanted to do until quite late in life, but by then I had a great background in all sorts of disciplines I could fall back on if I needed to. I do a lot of work for a major car manufacturer now and their training is abysmal, I work with engineers who had to pay their own course fees and struggled to get time off to go to college.My plumbing was mainly industrial though and steel rather than copper. I once fitted a bathroom suite for £30!! It cost me more for tools, which is when I made my mind up never to work in people's houses, unless I couldn't do anything else.
In reply to arch:
Which I why I recommended leaving the 32A one in.
You seem to have a very strange attitude to learning useful information.
> .......But it won't will it. Remember ??
> Thu 25 Feb 20:41
> "OK, now here's the important bit, a 32A type B breaker will allow a current of approximately 45A for at least 10,000 seconds (that's nearly 3 hours)"
Which I why I recommended leaving the 32A one in.
You seem to have a very strange attitude to learning useful information.
In reply to krikoman:
Hahaha, I can't wait until Arch sees that!!!
> Ha ha, I actually served my apprenticeship as a plumber / welder
Hahaha, I can't wait until Arch sees that!!!
1
In reply to krikoman:
If I need to know the bending radius of 1/2" Copper, I'll know where to come.........
> You seem to have a very strange attitude to learning useful information.
If I need to know the bending radius of 1/2" Copper, I'll know where to come.........
In reply to arch:
It seems I was right.
> Now you've blown it!! (Pun intended)
> Don't worry though. It wont be long before some know-it-all will be here.
It seems I was right.
In reply to arch:
Well at least you can pride yourself in that you got something right eh?
> It seems I was right.
Well at least you can pride yourself in that you got something right eh?
1
In reply to arch:
Or the current carrying capacity of a 32A Type B MCB
> If I need to know the bending radius of 1/2" Copper, I'll know where to come.........
Or the current carrying capacity of a 32A Type B MCB
In reply to JLS:
Since it clearly works fine the only good reason to change the breaker would be if you couldn't safely secure 10mm2 cables into its terminals. I don't expect you'll have that problem.
jk
> Edit: Re: why change the 32A mbc. Have I got it right that it currently works only because of the time curve mention above and if I did have long full heat showers it would eventually trip?
Since it clearly works fine the only good reason to change the breaker would be if you couldn't safely secure 10mm2 cables into its terminals. I don't expect you'll have that problem.
jk
In reply to Lusk:
In many offices of many companies across the country, you will find people who start out their career on the tools. After a short while some of them simply can't cope with getting their hands dirty any more. It's not their fault. It's too cold in the winter, too hot in the summer, nowhere for a pi*s, blah, blah, blah. Any excuse to stay in the nice Air-conditioned office.
Lots of these people are very intelligent, got lots of letters after their name, they can quote the rules and regs until the cows come home, always got the latest PPE too. But, give them a spanner, a hammer or woe-betide a power tool, well, you might as well forget it. You'll spend more time fixing what they break.
TBH, they're best off in the office, out the way of the "Doers"
In many offices of many companies across the country, you will find people who start out their career on the tools. After a short while some of them simply can't cope with getting their hands dirty any more. It's not their fault. It's too cold in the winter, too hot in the summer, nowhere for a pi*s, blah, blah, blah. Any excuse to stay in the nice Air-conditioned office.
Lots of these people are very intelligent, got lots of letters after their name, they can quote the rules and regs until the cows come home, always got the latest PPE too. But, give them a spanner, a hammer or woe-betide a power tool, well, you might as well forget it. You'll spend more time fixing what they break.
TBH, they're best off in the office, out the way of the "Doers"
1
In reply to arch:
We have them, and the guys who are still on the tools often suffer from them.
There is a saying , the longer they are away from the tools, the faster they get.
Typically they mean these guys who move into estimating jobs, once away from getting their hands dirty, they think the trades should be able to do the job quicker .( Quicker than they ever did the job themselves)
> In many offices of many companies across the country, you will find people who start out their career on the tools. After a short while some of them simply can't cope with getting their hands dirty any more.
We have them, and the guys who are still on the tools often suffer from them.
There is a saying , the longer they are away from the tools, the faster they get.
Typically they mean these guys who move into estimating jobs, once away from getting their hands dirty, they think the trades should be able to do the job quicker .( Quicker than they ever did the job themselves)
2
In reply to JLS: If the cable is in the roof, before you pull old one out, tape the new one to it and use it as a mouse/pully.
Plumbing, put in an isolating valve in the tube, somewhere that is easy to get at but out of site.
Good luck!
Plumbing, put in an isolating valve in the tube, somewhere that is easy to get at but out of site.
Good luck!
In reply to Stu Tyrrell:
No dont put it out of site, better to put it out of sight!!!?????
DAAAAAARRRRRRRR
No dont put it out of site, better to put it out of sight!!!?????
DAAAAAARRRRRRRR
1
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