RCD tripping

[SpottyDogs]

Hi, the RCD on my consumer unit has tripped and will not turn back on (just trips instantly). I have found that if I turn the MCB off that feeds just the external garage, I can turn the RCD on and it stays on.

So the problem seems to be with the garage. I have tried to unplug each item in turn (electric door, tumble dryer etc) and then flick the MCB back on but it instantly trips the RCD again. I can only assume the fault lies with the cable between the house and the external garage, does that sound about right?

Many thanks!

 

[EFLImpudence]

I can only assume the fault lies with the cable between the house and the external garage, does that sound about right?

Yes, including to the sockets etc.

Suspect moisture in one of the accessories leaking current from Line(live) to Earth or Neutral.

 

[SpottyDogs]

Thanks EFL, I have unplugged all appliances and it still happens, so could assume it's either moisture ingress to main power socket (garage doesn't have its own consumer unit), or an issue with the cable.

I can't see any obvious water ingress but would atmospheric moisture cause an issue? Just thinking with all the rain we've had recently.

Cheers

 

[EFLImpudence]

I can't see any obvious water ingress but would atmospheric moisture cause an issue? Just thinking with all the rain we've had recently.

Not if I understand correctly what you mean but perhaps invisible ingress - or condensation.

 

[SpottyDogs]

So the power comes underground from the house to the garage. This just comes through the garage floor in conduit and into a single socket. All appliances are connected (by use of a 4 gang extension) to that one socket. When I unplug everything from that one socket, the RCD still trips.

I'll see if I can get the face of the socket off and check for condensation or something. Thanks!

 

[EFLImpudence]

If you can't see anything perhaps it would be wise to disconnect the socket and make the cable safe then try again.
There might be damp insects inside the socket parts.

If that doesn't cure it then, from what you say, all that is left is the cable itself.

 

[ericmark]

An RCD detects an imbalance between the lives, that's line and neutral. With a line to earth fault turning off an appliance with find it, but with a neutral to earth fault, the load will increase the potential difference neutral to earth, and so also how much leaks, so any load can seem to be the fault.
We have a range of meters, which can be used to help find the problem, but they cost around £30, £90, £35 so not really worth the DIY guy buying. OK I have all three, but I was an electrician before I retired, so although now DIY, it was my trade.

So we are looking at which is the cheapest, buying test equipment, or paying an electrician? The first one will likely find the fault, so a google will likely find one we see some really cheap testers but as to how good they are I don't know.

 

[Murdochcat]

If you can't see anything perhaps it would be wise to disconnect the socket and make the cable safe then try again.
There might be damp insects inside the socket parts.

If that doesn't cure it then, from what you say, all that is left is the cable itself.

Not sure I agree with this.

It’s virtually impossible to advise on such issues over the internet

I would leave the garage isolated for a few days and if the problem remains, get a local competent spark to investigate.