Strange RCD fault

[fattony]

Hi

I've been investigating a strange RCD fault in my house this afternoon, there are only 3 circuits on the RCD, GF sockets, 1F sockets and Garage.

It's a Crabtree board installed around 2000

I've tested the RCD a few times at 0.5 and at X1 both test fine, traced the tripping to GF sockets, unplugged everything but still tripping, insulation resistance test is fine.

For some reason when I switch the RCD on and then a MCB the RCD trips again, I can do this numerous times and after a few attempts the RCD stays energised.

I managed to have the RCD stay on and the GF sockets and started plugging appliances back in, fridge trips it out instantly, left it unplugged and reset the RCD, it eventually stays on, bingo I thought, switched 1F sockets on and that tripped the RCD.

I can't imagine 2 faults developed at the same time on 2 circuits so I'm wondering if it's the RCD, anyone had a similar problem?

Thanks

 

[michaelw6]

has this been working fine till recently?
what might have changed?
have you had alot of rain?
you can try a load on the rcd with out the mcbs/sockets circuits connected.(do you have a spare mcb 16a)

 

[Midwest]

Have you ramp tested the RCD? Have you checked your earth leakage at source? Fault on one side can affect circuits on another side. Excuss ignorance, what's GF & 1F?

 

[fattony]

Apologies Ground floor and 1st floor.

This has been working fine until recently, no rain today and light rain if any over the last few days.

Nothing has changed as far as I'm aware.

Unfortunately my meter doesn't have ramp test function, I've moved the ground floor sockets to non RCD side so we can cook dinner and don't lose the food in the freezer, left RCD on for last 2 circuits its tripped again but even with MCB off the RCD will not energise, could the RCD be faulty?

 

[Pete999]

Have you ramp tested the RCD? Have you checked your earth leakage at source? Fault on one side can affect circuits on another side. Excuss ignorance, what's GF & 1F?

Er Ground Floor 1st Floor

 

[westward10]

Er Ground Floor 1st Floor

It's too much

 

[Octopus]

Hung any pictures recently?

 

[SJD]

I can't imagine 2 faults developed at the same time on 2 circuits so I'm wondering if it's the RCD, anyone had a similar problem?

Are you sure everything you are plugging in does not have a fault, e.g. poor IR (e.g. fridge) or even an appliance with a N to E short (or wrongly wired plug). Did you complete the 3x IR tests on each circuit individually, if so what results? And when you said everything was unplugged from each circuit, are you sure (L to N IR test will likely show up any unaccounted loads).

It is quite possible there are several causes of earth leakage, that individually won't trip the RCD, but when combined will.

 

[fattony]

Nope no pictures hung, no decorating nothing.

I did wonder about a combination of small earth leakage from different circuits but upstairs for example there is a tv, bedside lamp in each bedroom and a cordless phone charging base.

I only did IR on the ground floor sockets as at that time I thought the fault was there, I did L/N to earth and the result was greater than (I never remember if it's < or >) 200M

Have to pull out the dishwasher and washing machine hence L/N to earth

It's strange with no load on the RCD ie MCB off it won't energise at all?

 

[fattony]

RCD is now holding in with garage on but not 1st floor sockets, it's a little random

 

[westward10]

Have you checked for loose connections.

 

[Midwest]

Have you ramp tested the RCD? Have you checked your earth leakage at source? Fault on one side can affect circuits on another side. Excuss ignorance, what's GF & 1F?

Doooohhh!

 

[telectrix]

easy to remember the difference between > and <. jiust remember that the arrow points at the smaller one. my old maths teacher at school taught us that it was "the finger of scorn".

 

[SJD]

I did wonder about a combination of small earth leakage from different circuits but upstairs for example there is a tv, bedside lamp in each bedroom and a cordless phone charging base.

I only did IR on the ground floor sockets as at that time I thought the fault was there, I did L/N to earth and the result was greater than (I never remember if it's < or >) 200M

Have to pull out the dishwasher and washing machine hence L/N to earth

The tv, bedside lamp and cordless base are unlikely to have any leakage - unless plugged into a mains distribution board with mains filtering built in. Not impossible one of them is wired incorrectly in the plug (I did once find this at a rental property, a standard lamp with N & E swapped).

I would do the IR tests on all three circuits, don't assume the other two are OK.

And dishwashers and washing machines are up near the top of my list of things with leakage to cause tripping (another rental property, the dishwasher tripped at a specific point late in the cycle).

 

[Richard Burns]

I would say that if the RCD trips and will not energise when the MCBs are off then there is a Neutral earth fault. Because you can get the RCD to stay on then I would assume the fault is very close to the limiting resistance for the RCD to trip i.e ~7667 ohms (dependent on supply voltage).
This should be very clear cut on an IR test, so I would test the other two circuits.
I would suspect the garage as being the most likely to suffer from circuit damage, but appliances can fail at a any time.
Isolating one of the circuits and powering the others and sequencing through the isolations could also find it, if you are keen to do live testing!

 

[Octopus]

WOT he said ^^^^

Last Friday I went to a house where the RCD wouldn't reset even with all the MCB's off - and the culprit was a new picture hook about 3 foot up the wall from the CU. Great continuity from the MET to the picture hook!

Re pulling the appliances out - this is precisely why I won't install sockets behind white goods any more - sooner or later the RCD will trip and the homeowner or a spark will need to isolate the circuit properly. IMHO you can't investigate a tripping RCD when you have to link L&N together!

 

[fattony]

Havent had much time to look at this today but I did an IR test on the garage and it was <200M, disconnected it from the DB anyway as logic tells me its more likely to be the garage than the upstairs sockets

RCD is holding in and my next move if it stays in will be to move the ground floor sockets back.

Regarding sockets behind white goods, whats your method now then? Years ago we used to install switched spur above worktop controlling a socket lower down, I've carried this procedure on even though its not a requirement of 7671

Thanks

 

[telectrix]

always a good idea to fit the appliance socket in back of an adjacent base unit. i went this way some years ago when , with the socket behind a washing machine was fitted, the bloody machine would not go back as the plug/socket was tight against the metal back of the machine when it still needed to go in another inch.

 

[Dave OCD]

always a good idea to fit the appliance socket in back of an adjacent base unit. i went this way some years ago when , with the socket behind a washing machine was fitted, the bloody machine would not go back as the plug/socket was tight against the metal back of the machine when it still needed to go in another inch.

Very frustrating I'd imagine.

 

[fattony]

Do you still fit a spur above or just the socket outlet?

Update, found the fault, it was a redundant flood light which had been spurred off the upstairs ring

 

[Dave OCD]

Do you still fit a spur above or just the socket outlet?

Update, found the fault, it was a redundant flood light which had been spurred off the upstairs ring

If the socket is in a kitchen base unit it's easily accessible for isolation so IMO another isolator is unnecessary.

 

[telectrix]

Do you still fit a spur above or just the socket outlet?

Update, found the fault, it was a redundant flood light which had been spurred off the upstairs ring

bet it was a N-E fault and/or water ingress

 

[hightower]

Can't believe it took 15 replies until someone mentioned N-E fault. Surely with these symptoms that was the obvious place to look.

Had a mate say every time he turned the outside lights on at the switch it tripped the RCD - full to brimming with water.

Funnily enough, just looked at PIR floodlight for a mate - was working fine with the PIR half full with water. Opened it up and emptied the water and it stopped working.

 

[Jacek Buczak]

Yep tripping rcd sometimes a lot jobs.Last times I have 2 problems with tripping is well one emergency lights water inside ,second times I disconnect every E wire from every outlets socket to find where is problem and problem be in spur from outlet socket with power to strips lights on ceiling.Problem do it lights.

 

[Pat H]

After that much troubleshooting I'd be inclined to drop a new RCD in. it could be intermittently faulty.

 

[westward10]

Yep tripping rcd sometimes a lot jobs.Last times I have 2 problems with tripping is well one emergency lights water inside ,second times I disconnect every E wire from every outlets socket to find where is problem and problem be in spur from outlet socket with power to strips lights on ceiling.Problem do it lights.

Are you a wanna be rapper.