Ring main tripping RCD with nothing plugged in

[JLow75]

Hi all Electrical section,

I have a problem with one of my ring mains - it keeps tripping the main RCD, I spent the whole of saturday narrowing it down to which one & I have now disconnected it from the consumer unit, as to get house up & running again.

The house has a conservatory & loft conversion & has 3 ring mains (done in 1999 as far as I can make out from the history of the property)

This is what I have done so far & it has had no effect:

1. Removed everything from the sockets on the faulty ring (I think!) including disconnecting some fused spurs
2. checked with a meter for shorts between phase & Earth & phase & Neutral - none
3. tried a different MCB

Alot of the sockets are in the conservatory it's very cold & damp in there at the moment - so could it be damp/water issue?

Could the RCD itself be faulty - obviously highly unlikely as the other 2 rings are fine - fully loaded, all high current devices - heaters/kettle/immersion etc working fine

some of the wiring in the house is a right mess! - wiring & spurs everywhere, especially in conservatory.

The other 2 rings are fine & the faulty ring does not trip the 32A MCB - only the main

never had a problem with it in 6 years - it's just happened overnight.

So I am looking for some fault finding advice - is it now just a case of removing each socket & inspecting the integrity & condition of the wiring?

I am a 20 year time served Electrical technician (just not domestic!) and can borrow any test equipment from work if needed.

Any advice welcome thanks in advance

 

[Taylortwocities]

When tracing earth leakage problems, it is important to remember that the RCD can trip if it detects fault on the line OR the neutral side. In some cases, switches and MCBs only isolate the LINE half of the circuit, so you can run around in circles unless you have double pole switches on every circuit.

A meter is OK for finding "shorts" but you will be hunting for something like a fault of less than 2MΩ. To test for this you'll need to borrow an Insulation Resistance tester. This tests the circuit by stuffing 500V (DC) up the circuit, so make sure everything is disconnected before pressing the test button! A visual inspection can be done too, but an IR tester is the proper way of doing it.


And yes, water and damp is the main cause of these problems. Start with any lights, sockets that are outdoors first.

 

[JLow75]

Thanks - yes we have a Megger at work I can borrow.

I'm pretty sure everything is disconnected - but like I said it has seen a lot of bodging by previous owners! there is no pattern to the sockets at all - they are spread out all over the place, some in conservatory, some in loft & upstairs lol

 

[Echo the husky]

Did you check between neutral and earth?