Nuissance tripping on a 30mA Main RCD on a TT system

[Deleted member 26818]

Sounds like cumulative earth leakage.
You will most likely have to provide each circuit with individual 30ma RCD protection.

 

[toploader2010]

I have checked the continuity of the ring main and all is well. i have isolated all the circuits and switched back on and it doesnt trip. It is tripping with randomly circuits and not a particular circuit unfortunatly.

The RCD is tripping on half load with other circuits connected.
i will test the Rcd without any outgoing connections and see if it still trips on half load.

I will have to see if i can borrow a meter with ramp testing, mine is a old robin that doesnt have the ramp test function.

Can i use a current clamp and modify a extension lead so the earth is accessible and connect the ext lead to socket then connect my device to the ext, put my current clamp on the earth and measure the current leakage when the device is on. will this be ok?

 

[Engineer54]

I have checked the continuity of the ring main and all is well. i have isolated all the circuits and switched back on and it doesnt trip. It is tripping with randomly circuits and not a particular circuit unfortunatly.

The RCD is tripping on half load with other circuits connected.
i will test the Rcd without any outgoing connections and see if it still trips on half load.

I will have to see if i can borrow a meter with ramp testing, mine is a old robin that doesnt have the ramp test function.

Can i use a current clamp and modify a extension lead so the earth is accessible and connect the ext lead to socket then connect my device to the ext, put my current clamp on the earth and measure the current leakage when the device is on. will this be ok?

Not with a conventional current clamp meter, you need a leakage amp clamp that will have a microhm resolution. Also a lot of MFT kit do not ramp in 1mA steps, but in maybe 2 or 3 mA so not a very accurate method of testing leakage trip levels.

 

[Octopus]

If you can't locate one issue, which is very likely, I'd be talking to the client about a new dual RCD board or if the house is old, a board with a full set of RCBO's

Having one 30Ma RCD up front is a very undesirable situation for any household!

 

[toploader2010]

thanks for you response