/ RCD Tripped - Again

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mypyrex - on 15 Feb 2013
Last month I mentioned that the RCD on our Consumer Unit had tripped. Well this morning I got up to find it had tripped again and it wouldn't stay on again until I'd isolated some of the ring main sockets. All are switched back on again now and the RCD has not tripped again.

I also noticed that the fuse for the CH boiler switch had blown. It's a 3amp fuse. Just wondering if there's likely to be a connection(sorry about the pun)
nniff - on 15 Feb 2013
In reply to mypyrex:

Every time a light bulb blows in our house, the RCD trips. So you switch on a light, there's a pop as the bulb goes to meet its maker and half the house is plunged into darkness.


Seems likely to me that there's a connection.
gethin_allen on 15 Feb 2013
In reply to mypyrex:
I've had a few odd RCD tripping incidences recently too.
At first I thought it was due to dodgy wiring in the kitchen but I had the kitchen rewired recently with a total new circuit ready for the new kitchen installation.
Yesterday it tripped again when the 20A switch feed to the dishwashers hidden plug was turned on. now I's thinking it was the dishwasher playing up all along.
It doesn't bother me too much at the wiring needed doing anyway so I've not paid for a unnecessary job, but it does bother me re. the dishwasher.
sounds like you have something dodgy with the boiler tripping it when the timer kicks in in the morning.
jkarran - on 15 Feb 2013
In reply to mypyrex:

Is 3A the right fuse for the boiler (it seems reasonable to me but I don't know)? Sounds like you might have a fault on the boiler or whatever else is connected (thermostats, timers, heating pump).
jk
999thAndy on 15 Feb 2013
In reply to mypyrex:
The blown fuse and tripped RCD are probably linked. The RCD is measuring the current in the live vs the current in the neutral as it should all come in on the live, and all go out on the neutral. If any gets lost along the way the RCD trips - which is what happens when a fuse pops, because for a very brief period the current in the live is more than that in the neutral.

FWIW our consumer unit is split so that the lighting rings are not on the RCD - hence it doesn't plunge us into (entire) darkness when a bulb goes.
Ridge - on 15 Feb 2013
In reply to 999thAndy:
Domestic RCDs do seem to be really twitchy. Like you a I'd agree a split consumer unit is the way to go.
mypyrex - on 15 Feb 2013
In reply to 999thAndy: Thanks. Seems logical, I'll keep a check on it.
richyfenn on 15 Feb 2013
In reply to 999thAndy:

A fuse blowing tripping an RCD? Even when blowing there should always be equal current in Live and Neutral. Tripping a circuit breaker I can understand.
gethin_allen on 15 Feb 2013
In reply to Ridge:
"Like you a I'd agree a split consumer unit is the way to go."
split units are the norm for new stuff apparently, and as of the latest regs both parts have to be on RCDs not just one on RCDs (plugs and stuff)and the other on MCBs (lights and alarms).
The real development I think would be if consumer units with RCBOs so that each circuit is individually covered by a RCD.

999thAndy on 15 Feb 2013
In reply to richyfenn:
> (In reply to 999thAndy)
>
> A fuse blowing tripping an RCD? Even when blowing there should always be equal current in Live and Neutral.

Only if the fuse blows because it's too small.
Mark Edwards - on 15 Feb 2013
In reply to richyfenn:
> (In reply to 999thAndy)
>
> A fuse blowing tripping an RCD? Even when blowing there should always be equal current in Live and Neutral.

When a bulb fails (and presumably the same for fuses) there can be an arc as the element breaks. The arc can cause a current spike that causes the RCD to trip (non linear relationship current/voltage IIRC).

In a kitchen I would suspect something inductive such as a fridge/freezer causing the current leakage.
arch - on 15 Feb 2013
In reply to mypyrex: Don't you just love RCD's ??

When i was re-wiring houses, we had loads of problems with RCD's. We would finish the re-wire and turn the power back on and see what appliance would trip the RCD. Mainly the Cooker. Not nice telling an OAP that their old Cooker that was working before we re-wired their house in now no longer any good.

As an aside. I was called out earlier this week to change a 315amp fuse in a Transformwer that fed a whole housing estate. Never found out what blew that. Fuses do sometimes just fail.

iskra2000 - on 15 Feb 2013
In reply to mypyrex:
You said the 3A boiler fuse blew. Check the central heating pump ( inside the boiler if a combi) for leaks, timescale. Could be the problem.
DancingOnRock - on 16 Feb 2013
In reply to iskra2000: My friends boiler had a chaffed wire on the fan. Would run ok for a while, until wire grounded on metal casing then pop, fuse and RCD both go.
richyfenn on 16 Feb 2013
In reply to Mark Edwards:
> (In reply to richyfenn)
> [...]
>
> ... The arc can cause a current spike that causes the RCD to trip (non linear relationship current/voltage IIRC).

Ah that sounds more feasible now :)

When I rewired our house and fitted a new consumer unit (to replace the wooden one) I split everything between two RCDs. Kitchen ring (fridge/freezer) separate from the cooker. Upstairs lights with downstairs rings separate from downstairs lights with upstairs rings. So if an RCD trips for the upstairs lights then the upper rings should still be on so we can still have some light (TV or table lamps).

Most of the likely RCD trippers (oven, TVs) are quite new and made not to leak to earth so shouldn't cause issues, so far so good :)
Jim C - on 16 Feb 2013
In reply to mypyrex: we have had nightmares for years with RCCZD tripping, got up this morning to find again that it had tripped again.

It is a busy house, lots going on all the time daughters , with their gadgets , boyfriends staying over with theirs, son in law plugging in stuff here and there, as well as the normal stuff.

It can go 3/4 times a day or not for months. I have tried isolating all the circuits in turn to see if there is a pattern when I turn them back on to see if it trips, but it seems random.

I was going to change the RCD out, but, I have a feeling that it might be more to do with 'spikes' in the supply, otherwise how could it cope with MONTHS of the busy household stuff, all the gadgets, power tools. and all the stuff that switches on and off, boilers, fridges, freezers, dishwashers, tumble dryers , hair dryers ,straighteners,etc. etc. and then.go 5 nights in a row, or 3 or 4 times in a day when nothing has changed?

Any clues out there? I don't want to waste money on a new RCCD and a spark if I don't need to.
richyfenn on 16 Feb 2013
In reply to Jim C:

I experienced this sort of thing at work a few weeks ago. We were setting up a lot of equipment fed from two 16 amp connections with RCDs. They are RCD protected as catering trucks usually plug into them. It was the evening and whilst we were chatting (thus not changing anything) both RCDs tripped, this was after being on all day. We turn them back on and a minute later they go again. This went on for a few minutes and then everything was fine and they didn't trip again. Spooky PITAs.

In your situation you do have a lot going on. How many RCDs do you have? My unqualified guess would be to add one or two more to spread the load, or see if you can get different ones fitted that have a higher tolerance. Domestic RCDs are very sensitive, but you can get others that don't trigger quite so quickly or easily, with the caveat of not being quite as safe.
*Unqualified guess*
DancingOnRock - on 16 Feb 2013
Anything with water heater elements in them are main culprits.

Washing machines, dishwashers etc
Philip on 16 Feb 2013
Someone's probably said it, but it's worth emphasizing that an RCD triping is not necessarily a sign of a fault on the circuit with the load. A neutral-earth fault on any circuit can cause the trip when a high load kicks in. For example, so corrosion or damage to the lights could cause the fault when you use a power drill plugged into a ring main.

The only correct diagnosis is to disconnect any check each circuit as the CU.
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Ridge - on 17 Feb 2013
In reply to mypyrex:

Oh for the good old days when replacing a fuse with a nail easily solved these issues..

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