RCD trips (Ed.)

[Kantilal Tanna]

I have boiler and under floor heating connected to 3 amp fused switch, it some how trips RCD in mains fuse box. There wii be no power to lights. This does not affect power to other items like washing machine, oven, microwave.
I tried to reset trip switch but it wouldn’t let me do it so I turned off 6-10( as per photo) and after resetting and turning one by one, it trips as soon as I tried switch marked 6 radiators it trips.
After putting new 3amp fuse it works fine.
Please can anybody give me idea what might be wrong.
Thank you.

 

[chivers67]

This could be caused by a Number of issues. Often it's caused by Water Ingress, with the fuse off check to see if there is any water present on the circuit. Is there a fused connection unit feeding the boiler / under floor heating? Are there two separate ones for each or one for both?

 

[Kantilal Tanna]

Hi,
Thank you. At present it is one switch for underfloor heating. Boiler connecting has been removed and it is now plug into wall socket.
I will check the switch to see if there is any dampness or water.
Many thanks.

 

[ericmark]

There are three meters to find the problem, the RCD tester clearly tests the RCD, I would not expect a problem with the RCD, the clamp on ammeter tests the leakage, but will only work if the RCD holds in, so the insulation tester will work with non energised circuits, but uses DC so will not detect inductive and capacitive leaking. I paid £35 each for the latter two, so the aim is to try to find the fault without the meters.

You have it seems worked out something to do with the B16 MCB, earth to neutral faults can be misleading so can't be 100% sure, but it seems likely.

After putting new 3amp fuse it works fine.

This is the odd bit, why fitting a 3 amp fuse should stop it tripping I don't know, would have expected the reverse, so I am wondering if we have some thing like a borrowed neutral. But been scratching my head to think of a scenario that would cause this, and I have failed.

So I am watching this thread to see if anyone else has some ideas.