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!