Type AC RCD failing test

[vwes59]

Hi. Now I'm pretty sure why this is happening, but I thought I'd check.

Just did a standard RCD test at a client, and the RCD failed the test. Did a Ramp Test to check it and it finally tripped at 100mA. It's an AC RCD, so my guess is it's an appliance or something leaking DC current high enough to swamp the RCD. I know the simple solution would be to swap it out for a Type A, but I'd like to try and find if its a faulty appliance, LED light, dimmer switch and so on, as if there is a genuine earth fault, this RCD isn't going to work. My guess is the only way to do this is to methodically go round and try and unplug/isolate anything that might be inducting a DC current. The client hasn't reported any issues, I was simply there to put in an external socket (Yes I undid my work to check I hadn't caused the problem).

Any other thoughts ?

 

[Pretty Mouth]

The RCD needs testing in isolation from all down stream circuits, to confirm that it is working correctly without other influences. Disconnect the outgoing neutral conductor and switch all breakers off, then retest.

Old fridges sometimes slow tripping times for RCDs, something to do with capacitors supposedly. Look out for N-E faults too, these can sometimes blind RCDs