Could the RCD be faulty?

[spot5050]

Hi, I can't get an RCD to switch on at all, even with the main isolator switched off. Is that definitely a faulty RCD or could it be something else?

I have a metal 8-way Cudis CPN consumer unit with two RCDs, one with four MCBs and the other with one MCB. I originally switched the right-hand RCD off to add a new mains socket upstairs. After doing the work I can't turn it back on. I've tried putting all the wiring back to how it was before I added the socket but that RCD still won't switch back on. Then I tried turning the isolator and all the MCB's off but I still can't switch that RCD to the on position.

I'm a new forum member. Any hints greatly appreciated.

 

[James]

Could be faulty.
there is a possibility of changing the 2 rcds round and that may buy you some time whilst a couple of replacements can be found.

I would recommend getting an electrician in to do it though as they will test the new rcd and make sure it is working correctly.

 

[Marvo]

Every RCD I've encountered will reset if power is completely disconnected so I would guess it is a faulty RCD although there's a slim chance power could be being back fed into it. The only way to be 100% sure is to test it properly which, as James says would be a job for an electrician.

 

[spot5050]

Thanks both of you. I think I'll get a sparky to look at it as you suggest. I took the front off the consumer unit and the wiring inside is a mess. There are two tiny lego block connectors and one of them is charred and melted.

 

[westward10]

Can you put a pic up.

 

[brianmoooore]

There should be a label on or near the CU, informing you that the RCDs should be tested every 3months (now changed to 6 months). Have you been following this advice?
If a RCD is left for years without tripping, they will trip when they should, but often the reset mechanism will have become stuck, so it will not reset.
The charred connectors may or may not be anything to do with the problem, but obviously need urgent attention.

 

[spot5050]

There should be a label on or near the CU, informing you that the RCDs should be tested every 3months (now changed to 6 months). Have you been following this advice?
If a RCD is left for years without tripping, they will trip when they should, but often the reset mechanism will have become stuck, so it will not reset.
The charred connectors may or may not be anything t do with the problem, but obviously need urgent attention.

There's no label that I can see and I wasn't aware that they should be tested - thanks for the tip. I've never even had an electrician mention that before. Is it a legal requirement?

 

[brianmoooore]

The label is required as part of the electrical regs.

 

[spot5050]

Can you put a pic up.

 

[DPG]

Has there been a bit of moisture in there?

 

[spot5050]

Has there been a bit of moisture in there?

It seems dry but it is in a cellar. I can't see any obvious signs of rust in the consumer unit. I don't know if it has been damp in there in the past - I've just bought the house.

 

[DPG]

It seems dry but it is in a cellar. I can't see any obvious signs of rust in the consumer unit. I don't know if it has been damp in there in the past - I've just bought the house.

I can see some corrosion on some of the copper wires. Probably from some time ago then.

 

[spot5050]

Update:

It's fixed now. Thanks for everyone's comments, thoughts and suggestions.

I replaced the RCD and that has solved the issue. I've also called a sparky to get them to check everything over and sort out the burned connector block. I think I'll also get an EICR done for peace of mind.

While I had the front off the consumer unit I noticed that the left-hand RCD is daisy-chained off the right-hand RCD, so neutral goes from the bus bar to the right RCD then on to the left RCD. Wouldn't it have been easier to run both RCDs directly from the bus bar? That would avoid having to stuff two neutral cables into one connection on the right RCD.

 

[spot5050]

I can see some corrosion on some of the copper wires. Probably from some time ago then.

Ah yes, I didn't spot that.