RCD tripping intermittently

[dave50]

The RCD in my consumer unit has been tripping recently. There has been no change in appliances anywhere in the house or where they are plugged in. Sometimes it can trip every few hours then it will stop and might be a few weeks until it does it again or even a few months. There is no pattern to it whatsoever, it can do it night or day. I know it's not the kitchen ring main which includes all appliances , that is a different circuit and if I leave only that one on it never trips. The other ring is for the rest of the house and it is this one that is causing it to trip. i am getting sick of it now, is it possible to replace the RCD with a simple 2 pole switch? Yes i know it's safety device and shouldn't be removed but we used to have an old consumer unit with no RCD and nobody got electrocuted or died.

[rojash]

"Yes i know it's safety device and shouldn't be removed but we used to have an old consumer unit with no RCD and nobody got electrocuted or died."

Presumably you'd rather that next time, instead of the RCD tripping, the house burns down.

[The Builder]

Dave, you need to get someone in to run a few tests. I've had this before, and in one case I tested the RCD and found it was tripping on a very low current, well below the 24-30mA that they should operate at. I just replaced it.

An electrician would advise on possibly swapping circuits to overcome this. Possibly measuring earth leakage current as well.

Intermittent tripping is a pain. No DIY solutions I'm afraid.

[buildersmate]

Rojash: "Presumably you'd rather that next time, instead of the RCD tripping, the house burns down". It seems you don't understand the difference between what an MCB and an RCD actually do.

An MCB trips on overcurrent loading, which is a potential danger from excessive heat, which in turn may lead to a house burning down.

An RCD trips on an earth leakage fault, most commonly at 30mA differential between L and N. A 30mA trip is (in most circumstances) little enough current to avoid a death by electrocution, but 6W of power prior to tripping certainly won't burn a house down.

[johnk]

Try unpluging your appliances one at a time and see if there's a fault on any of them. Faults mostly occur on anything with an element

[boxtops]

whatever it is, it's happening to our ceiling lights at work - the fuse keeps tripping in our part of the building.

[BRIGHT SPARK]

rojash is right....if you withdraw the 30 mA protection the chances of a fire will increase...dont do it!

[rojash]

"A 30mA trip is (in most circumstances) little enough current to avoid a death by electrocution, but 6W of power prior to tripping certainly won't burn a house down."

Right - but an RCD trips at 30mA. That means 30mA OR MORE could be the cause of the problem. Take out the RCD, who's to say (without further tests) what the actually leakage current is?

[dave50]

I've tried the whole unplugging appliance theory but with the tripping having no pattern to it whatsoever it's impossible to ascertain whether any of the appliances are faulty. I could get home tonight and it won't trip for weeks then suddenly it will do it a few times in one day even though nothing has changed. It is so unpredictable. Incidentally, when it does trip I never have any trouble resetting it straight away, it then stays on for anything from about 2 hours to all day, again I never know what it will do.

[The Builder]

Dave, it could even be insulation breaking down somewhere, causing leakage to earth from live or neutral.
Do have someone run a few simple tests. One of the good guys would have the experience to know what to look for.
I know these things seem random and without a logical cause, but there's always a reason somewhere.
Put your mind at rest :o)

[BRIGHT SPARK]

dave....what else is on the side of the tripping RCD.What type of board do you have..is it a dual RCD type with main switch or single RCD with main switch and which side is the kitchen ring on.

[buildersmate]

Would you care to explain your answer, BS?

[BRIGHT SPARK]

BM...which part do you not understand?

[buildersmate]

"if you withdraw the 30 mA protection the chances of a fire will increase...dont do it!"
- unless you mean an increase by a proverbial gnat's whisker.

[BRIGHT SPARK]

BM as rojash says a 30mA RCD will give you entire protection from say 6ka DOWN to 25mA not from 0 up to 25mA.
It will trip if the FAULT CURRENT is 25mA or greater....it should not trip if its 24mA or less.(a 30mA RCD usually trips at around 25mA).What we are saying is ...if you withdraw the protection you are at higher risk and not by a gnats whisker.

[Clanad]

Admittedly, I'm struggl with some of the terms being used in this query... but here in the U.S. the device on the main circuit board to protect circuits (well, duh!) are called circuit breakers. They're devices t lo almost like a light swithc but harder to move. If the circuit is oberloaded it trips and then must be reset.
Thing is, they are spring loaded and we've had older ones that are doing what you describe. They trip for no apparent reason and then may remain perfectly normal until th enext time. What we've found is the spring mechanism has gone (as you Brits say)all wobbly. The actual circuit breaker is not very expensive and easily replaced if one is familiar with them and once replaced the problem never returns...

[The Builder]

Clanad... I see what you're saying. Your breakers are what we call MCBs (miniature circuit breakers)

What Dave has a problem with is what we call a Residual Current Device (RCD), and you know as a GFI ... Ground Fault Interrupter :o)))

[Clanad]

I kinda surmised that it might be a GFI, The Builder, but the same process works with our GFI's.

Here in the U.S. most GFCI protectors have a spring-loaded breaker button. When the GFCI senses a problem, the breaker button is “tripped.” The breaker button needs to be manually reset in order for the power to be re-established to the outlet. To reset a "popped" CFI circuit, one pushes the black button, which is also spring loaded. If it has popped (or been reset) a number of times (choose a number... zero to infinity) the spring mechanism becomes unsure of itself (so to speak) and can pop at times unrelated to load.
Last thought... is the RCD (GFI) housed in a box with other switches? I've seen GFI's prematurely "wearing out" and popping intemittently due to the heat generated by a nearby dimmer switch housed in the same receptacle box.