UKC

I've recently moved into a new house that had a conventional central heating system fitted at some point, but has since been converted to a combi system. In the upstairs airing cupboard where the hot water cylinder once lived there's a single socket sized fuse switch on the wall that can hold a typical cartridge fuse of the size that you'd find in any UK plug.

At first I thought it was just a switch for the old immersion heater or something, but having removed it from the wall to have a look at the back of it I'm now really confused as to what it did/does: there was no fuse in it when I got the house but there's still some flat, PVC insulated 1.5mm solid core twin and earth cable connected to it (red and black rather than brown and blue, so probably fairly old) and this is still live. The thing is, there doesn't seem to be any "output" terminal from the switch, so as far as I can tell, when there's a fuse in it and the switch is on, it's just a dead short across the fuse from live to neutral and it doesn't actually switch power to anything.

I've traced the cable from the socket and it runs up through the wall, into the loft and then across towards the other side of the house somewhere (I've not bothered taking up all of the loft insulation to follow it yet).

Can anyone explain what it's likely to have done/be doing and how it works? I'm obviously misunderstanding something.

In reply to Foxache:

Former electric shower? We had exactly the same in a slightly different configuration.

In reply to Foxache:

Probably was the switch for the Im’Heater, but who knows........
Switch wiring sound normal to me; both cores (R+B) to and from the switch are part of the Live line from the CU to whatever the appliance is/was.

In reply to ByEek:

What's got me confused is that there are only four terminals on the back of it (one for live, one for neutral and two earths) so you can only connect one cable to it and therefore I don't understand how it can switch power to anything else.

In reply to Foxache:


Sounds very odd, are you absolutely sure there are no more terminals for outgoing cables?

In reply to Foxache:

I would hop into the loft and see where it goes. If it is an old shower unit, it might have been partially disassembled / Eastern European metal theifs took half of it? Who knows.

In reply to Foxache:

Possibly a supply for a motorised valve on the old system?

At 1.5mm it was not running anything big.
I would wire up a ac radio, then throw all the fuses in turn at the box until it switches off, to see what ring it is on, or if it is perhaps individually fused.

In reply to Foxache:
Outside light?.........Loft light?.......

In reply to Jim C:




Could be that or possibly a central heating pump but still seems odd for it not to have terminals for an outgoing wire.

In reply to teflonpete:
Are the 4 terminals one live, one switched live, one neutral, one earth (usually separate from the main black bit containing the switch), just wrongly wired?

It does seem likely it'd be the immersion heater or a shower pump (but not an electric shower which tend to be wired back to their own circuit at the CU).

Neil

In reply to Foxache:
Four terminals, are they not live, switched live, neutral (2 cores into this one) and earth (again, 2 cores). Whatever was connected has been removed, maybe an immersion heater?

Wired as it is switching 'dead short' across the connected cores chances are it's a switched live (red sleeve or tape on the black core?) for something elsewhere in the house, something presumably still there and connected (live) if no longer needed/working (no fuse), maybe part of the old heating system a pump or valve, a towel rail, a ventilation fan or sump pump, maybe a loft light or motion sensitive outdoor light... you'd have to follow the wires really to be sure unless you fancy popping a fuse in and seeing what runs (might not be a great idea, it's likely decommissioned for a reason). It's also possible it was part of the tank thermostat system that has been left in place for no good reason.

jk

In reply to Foxache:

Does it have a hole in the front for a flex?

In reply to all:

I'll post a couple of photos of it, front and back, when I get home tonight if my internet has been sorted out as promised.
I may have made a mistake with the terminals at the back but there's no hole in the front for a flex to come out of.

The main reason I'm interested is because if possible, I want to use that cable to power a few lights up in the loft (maximum 400W and 1.7A), and it'd make life really easy as it runs straight past where the lights would be. At the last house I just ran another spur off one of the existing lighting junction boxes but either there aren't any junction boxes at this place or they're buried somewhere that I can't see.

In reply to Foxache:

I can virtually guarantee it is the old immersion feed.

There will be an 'output terminal' from the switch as they simply don't make switches that you can't connect to anything.


>as far as I can tell, when there's a fuse in it and the switch is on, it's just a dead short across the fuse from live to neutral and it doesn't actually switch power to anything.


Really? Are you positive? Is it blowing fuses or the circuit breaker? Should you really be messing with electrics?

You should be able to run your loft lights off the upstairs lighting circuit easily enough. The 'junction boxes' are actually at the ceiling roses - it's highly likely there'll be a permanent live and neutral at each rose so it should be easy to come off that.

In reply to Wulfrunian:

At 1.5 mm I seriously doubt it would be an immersion heater as it's just too small; 1.5 mm is lighting ring stuff.

I'm guessing something like a light or an extractor fan. Something with a fixed or ring feed and a switched live like you would have with a lighting ring where the ring goes around the house terminated at every light fitting with the wire running to this mysterious fused fitting (or otherwise a light switch) coming down from the positing terminal on the ring to the switch via the red of the t+e and then returning to the light fitting via the black. You would normally find a bit of red/brown tape or heat shrink on the black to identify that it can be live if the switch is thrown.

In reply to Wulfrunian:

I literally had about 20 minutes before work this morning to look at it, most of which was spent trying to find where the cable emerged in the loft. With regards to the switch itself I just got the multimeter on it to see if it was live and quickly eyeballed the terminals to see if I could work out what it was doing, but from what everyone is saying it sounds like I must've missed an output terminal or something then.

As for whether or not I should be messing with electrics, what's the harm? It's not like anyone ever died from messing around with mains electricity.

In reply to gethin_allen:

An immersion would usually be run in 2.5mm but:

a) this may well be 2.5mm cable

or

b) 1.5mm may be fine, depending on length of cable run and installation conditions. It can certainly handle well over 13A under the right circumstances.

By lighting ring, I take it you mean lighting radial?

I'm an electrical engineer by qualification and occasional electrician by trade. Just sayin' like....

In reply to Wulfrunian:
...


Well woopedy doo to you!
You can't guarantee that it is immersion heater feed at all can you? like...

would you rig up an immersion heater on 1.5 mm twin and earth? like...

So should you be making such assumptions for someone else to potentially follow and get in trouble? I'd have thought that as a "professional" you'd be quite wary of doing such things! like...

And do you need to have a dig at the OP in your post? "should you be messing with electrics?" it costs nothing to be polite and suggest that if he is unsure about anything he should probably consult a qualified person.

In reply to gethin_allen:

Oh do get over yourself dear boy. Like.

Immersion on 1.5mm? As I said, 1.5mm is capable of handling more than 13A under certain circumstances so why not? Please tell me.

OK, given the OP's clear lack of understanding, no he shouldn't be messing with electrics in my 'professional' opinion. Will that stop him? Unlikely. Why should it?

Kiss kiss sweetcheeks.

In reply to Foxache:

I'd say it was for the Immersion heater before the hot water tank was removed. There should ?? be a 15amp fuse/trip for it in the consumer unit. (May not be)

Are you sure the cable is 1.5mm and not 2.5mm, difficult to know accurately just by looking at it.

As regards the loft lights. Get one of these, http://www.screwfix.com/p/mk-13a-unswitched-fused-connection-unit-white/297... Stick a 5amp cartridge fuse in it and wire your lights of off that.

In reply to arch:



It is very easy, it printed ON the cable ( along with the BS standard) he just needs a better light. to read it.

No doubt you were all kept awake last night by this, but don't worry because I've had chance for a proper look and have now sussed it once and for all.

I disconnected the live cable (which is definitely 1.5mm) from the switch using a sharpened copper rod having just got out of the shower and perched on an aluminium stepladder, to ensure that any escaping bad electricity (from the negative wire) discharged safely over my body and into the hallway carpet. The cable had been obscuring two more screw type terminal connections at the very bottom and side of the switch, one marked 'N LOAD' and the other 'L LOAD'. I confirmed that there was continuity across those two terminals by inserting a fuse, connecting it back up to the mains, flicking the switch and then licking it.
Also obscured by the cable (and the fact that the switch box is quite low down on the wall) was a small hole drilled in the bottom of the bit that remains screwed to the wall, just big enough to get a flex through.

Mystery solved, so thanks for the help.

In reply to Jim C:


Really? I'll think you'll find that is a relatively new idea, and the OP did state an old fitting.

In reply to Foxache:



You're lucky to still be alive. The proper way of conducting that test is to have a 'wick' of rolled up wire wool dangling from your anus into a metal bucket full of water connected by crocodile clips to a car battery.

In reply to teflonpete:

It sounds like I should've left it to the professionals.