RCD tripping issue on ring circuit

[Josh Kav]

First time poster go easy on me.

Got a call out to a job today, got told the RCD was tripping. Even when no appliances plugged in. And so it was intermittently about every 20 mins. Only two ring circuits on the RCD, on one of the rings im getting continuity across line and netural on both legs. Its not taking the MCB out, no fault across the earth.

Tested the RCD for nuisance tripping all passed fine.

Cant get my head around why with a permanent short the MCB wont trip? Going back tomorrow morning for further investigation and feeling as if i should suggest re wire of sockets due to reasonably low IR readings anyway.

Any thoughts would be appreciated.
Cheers

 

[littlespark]

I only ever read the post buzz, never the comments lol. For all I know I could constantly be repeating what others say.....


Appliance still plugged in. Cooker hood, FCU will be behind chimney.
Even turned off at socket, can still get an N-E fault to trip rcd.
Have you checked the mcb isn’t at fault?

Buy yourself a notepad and a pencil. For taking notes.

 

[DPG]

Could do with proper test results. Your information seems a bit vague.

 

[dksanders]

Is the heating fed by one of these circuits? If the RCD trips yet you've got good IR readings that implies an intermittent fault which can be caused by e.g. the heating/water heating coming on and there's a faulty component (pump, valve, boiler pcb, immersion element), or a compressor motor kicking in.

A healthy ring circuit has a natural earth leakage of about 3mA, the power supplies for modern equipment such as TVs, PCs, phone chargers etc also have quite high earth leakage; when it trips it could it be the sum of these exceeding 30mA.

Does it trip when you're there and have disconnected everything, or when stuffs plugged in/switched on?

Is there e.g. a PIR external light fed via a FCU on the circuit?