Fusebox/RCD fault

[garviel]

Afternoon all,

I have a strange issue with my consumer unit that I would appreciate advice on.

My CU tripped yesterday morning on the socket ring circuit (the light circuit is working fine). I unplugged every socket but when i try to switch the socket ring back on at the consumer unit it won't go on (RCD trips immediately).

If I turn the RCD off, then the socket ring switch will stay on but then the RCD will not switch on.

Basically there is no time delay to tripping, non load on the circuit and no moisture at any of the outlets. Any ideas?

My electrician is on holiday for the weekend and if it is a big job such as raising floorboards etc then i would rather wait for him.
Garv

 

[EFLImpudence]

Is the socket circuit the only one controlled by the RCD?

 

[garviel]

Is the socket circuit the only one controlled by the RCD?

There are only 2 ring circuits in the flat - lights and sockets. The CU has room for 2 sets of 2 circuits protected by an RCD each. The lights are on one set (with an unused spare) and sockets on other set (also with an unused spare). I hope this makes sense!

Only the socket one trips it's RCD

 

[EFLImpudence]

Have any screws/nails been put in walls recently or any other work to the flat?

It's either -

A faulty appliance - nothing overlooked? - boiler (you can't usually isolate a boiler/heating system unless it is on a plug)
A faulty RCD - possible but not likely, or
A fault on the circuit causing an earth leakage.

Earth leakage can be caused by damage to a cable by screws, rodents, crushing, things like that.

I think you will need someone with the correct equipment to find it.

 

[garviel]

Have any screws/nails been put in walls recently or any other work to the flat?

It's either -

A faulty appliance - nothing overlooked? - boiler (you can't usually isolate a boiler/heating system unless it is on a plug)
A faulty RCD - possible but not likely, or
A fault on the circuit causing an earth leakage.

Earth leakage can be caused by damage to a cable by screws, rodents, crushing, things like that.

I think you will need someone with the correct equipment to find it.

No, no work on flat in the last year. Boiler is on a plug.

Sounds like a big job, at least in terms of lifting carpet and floorboards. sigh.

Thanks for your help!

 

[JohnW2]

Sounds like a big job, at least in terms of lifting carpet and floorboards. sigh.

It could be, but not inevitably - so I would suggest that you don't start pulling your hair out yet!

Kind Regards, John

 

[securespark]

Have you checked ABSOLUTELY everything is disconnected?

All plugs OUT, not just switched off.

Think about hidden sockets for appliances, immersion heaters, fridge/freezers etc....

All switches off.

Where equipment is connected by an unswitched connection unit, you will have to disconnect the outgoing cabling.

 

[EFLImpudence]

As I found once in a customer's house.

Socket, which had N and E the wrong way round, behind bed only tripped RCD when the daughter had plugged in her devices when she came home from school.

Edit - corrected.

 

[JohnW2]

Socket, which had N and L the wrong way round, behind bed only tripped RCD when the daughter had plugged in her devices when she came home from school.

Why did transposed L & N result in an RCD trip - was there also some other fault?

Kind Regards, John

 

[garviel]

Have you checked ABSOLUTELY everything is disconnected?

All plugs OUT, not just switched off.

Think about hidden sockets for appliances, immersion heaters, fridge/freezers etc....

All switches off.

Where equipment is connected by an unswitched connection unit, you will have to disconnect the outgoing cabling.

Checked it all. We've had no problems and no work done and yesterday just went off!

The only incident I can think of was an old toaster that tripped the RCD about 3 weeks ago. Got rid of toaster, got a new one, and everything has been fine since.

 

[EFLImpudence]

Sorry, N and E of course. I will correct it.

 

[garviel]

UPDATE: OK, had competent scheme electrician round - he tested the CU - no joy, then opened up every socket in the flat to test - still no joy. He tested the socket-circuit by connecting with the other existing RCD on the CU (the existing light circuit) - still tripped. Changed the RCD entirely - still no joy, still tripped.

As a last resort changed the RCD again to a third one - it worked!

He says he has never come across 3 faulty RCDs and it was a highly unlikely event/coincidence but it is now working.

I don't know what to think of it! I have however noticed that the amp rating of the new RCD is 100 while the old one was 63 - is that a problem?

 

[DetlefSchmitz]

No

 

[bernardgreen]

Based on your description of this "competent scheme electrician's" method of testing I would consider getting a second opinion.

He says he has never come across 3 faulty RCDs and it was a highly unlikely event/coincidence but it is now working.

Do you know if he did a ramp test on the RCDs I think it is possible that the earth leakage fault which caused the 3 RCDs to trip is still there and the RCD that does not trip is the defective RCD.

It may be "working" because the safety device, the RCD, is not operating when it should.

 

[JohnW2]

He says he has never come across 3 faulty RCDs and it was a highly unlikely event/coincidence but it is now working. .... I don't know what to think of it!

It does seem very odd, and I would have though very unlikely that the RCDs were solely (if at all) to blame. There must be some 'leakage' in the sockets circuit for it to cause the 'lighting' RCD to trip when it is connected to that RCD, given that that RCD does not normally trip. As bernard has said, I would be inclined to suggest that you get a second opinion.

At the very least, if the electrician's interpretation is correct, then the other RCD in your CU would also need replacing. Do I take it that he didn't do that?

Kind Regards, John