Nuisance tripping has stumped our sparky...

[Figaroflynn]

For the past few weeks, we have had one of two socket circuits tripping about once a day, including at night and day, in all weathers.

The wiring is by no means new, but the consumer unit was installed only 2 years ago and the wiring fully checked. There are a few clear indications of 'DIY' jobs (three light fittings in the centre of the master bedroom?!), and we aren't fully clear as to where some of the ring circuits and spurs are.

Following advice online, we systematically switched off (and, where possible, also unplugged) each appliance on this circuit. This involved trailing cables out of windows into the garage to power freezers etc. -- our electrician assures us that we did a thorough job! Still no indication of any offending appliance to blame.

The electrician that we use -- I should add -- is 'tried and tested', not just by us but also by various relatives in the building trade who have worked with him. In his first visit, he spent in excess of 4 hours removing socket covers and testing appliances. He also examined the garage wiring and appliances, plus outdoor sockets and lights.

The strangest -- and really only -- finding was a surge on his meter when it touched a small nail in the wall. This has been there since we moved in. The electrician removed about a square inch of plaster around this, after removing the nail, but there was no pierced wire.

After he left, frustrated and apologetic, we hoped that the tripping might just stop. He'd queried that two sockets in the kitchen might be subject to condensation. However, as these had been switched off and not had plugs in them, with the tripping still happening, this seemed strange.

We asked the electrician directly if we needed a rewire, but he assured us that, even with a completely new rewire, he would be very happy with the readings he had got on the circuit, and that they are well within the 17th ed. requirements.

We've also had confirmation from a boiler fitter, happening next week, that the pump and transformer are on their way out/dodgy.

My main query is this: could faulty appliances that are switched off but still connected (e.g. boiler, cooker), still be at fault?

The electrician has since also replaced the RCD attached to this circuit AND IT IS STILL TRIPPING!

Please help!

 

[Echo the husky]

What sort of insulation resistance readings was he getting?

 

[flameport]

My main query is this: could faulty appliances that are switched off but still connected (e.g. boiler, cooker), still be at fault?

Yes they could.
Switches are often only single pole, leaving the neutral connected. A fault between neutral and earth in the appliance can result in an RCD tripping depending on the load on the rest of the circuit and other circuits connected to the same RCD.

Same applies to the kitchen sockets - although they may be off, the wiring at the back and the terminals inside are still connected.

 

[Figaroflynn]

What sort of insulation resistance readings was he getting?

He said between 1 and 6MΩ. It got gradually higher as he went on and shot up when he attached his meter to that nail...

Thanks for your reply.

 

[Figaroflynn]

My main query is this: could faulty appliances that are switched off but still connected (e.g. boiler, cooker), still be at fault?

Yes they could.
Switches are often only single pole, leaving the neutral connected. A fault between neutral and earth in the appliance can result in an RCD tripping depending on the load on the rest of the circuit and other circuits connected to the same RCD.

Same applies to the kitchen sockets - although they may be off, the wiring at the back and the terminals inside are still connected.

He didn't check the cooker wiring, for example, and I don't believe he removed the fuse from the boiler, so I'm guessing either of these may be the culprit...? As you can tell, I'm not electrically enlightened! Advice much appreciated.

 

[Figaroflynn]

What sort of insulation resistance readings was he getting?

And he gave it the full 500V.

 

[DaveHerns]

What made him put his meter on the nail?

 

[Echo the husky]

One of mine goes up to 5000V...
Those readings are poor but acceptable, providing that is the reading for the whole installation and not just one circuit. How many RCDs do you have, and how many circuits does it/each one supply? Post a photo of the DB if you are unsure.

I would consider those readings as not good and would generally aim for a minimum of 100MΩ for each circuit before I'm happy.

I assume he was disconnecting the neutral wires at the DB when trying to narrow things down?!

The nail reading could just be from damp in the wall.

Other odd fault I have had, floorboard nail through cable, intermittently caused fault when someone stood on that part of the floor.

 

[Figaroflynn]

What made him put his meter on the nail?

I think he was just ruling anything out. He'd been asking about a thermostat near to the nail, wondering how it was attached to the wall in case we had pierced a wire.

 

[bernardgreen]

A fault between neutral and earth in the appliance can result in an RCD tripping depending on the load on the rest of the circuit and other circuits connected to the same RCD.

Neutral_Earth_trip

• bernardgreen
• 16 Jan 2011
• 48

 

[crystal ball]

For your reference I will relate some intermittent tripping tales I have been involved with:
Main RCD tripping every time freezer was plugged in, aha thats an easy one (not), cause of fault was a burned neutral in a shower

Socket RCD tripping randomly, leaking pipe at back of cylinder cupboard dripping through gap in floorboard onto a JB

Cooker MCB tripping randomly, screw through cooker cable fault was clearing itself as someone walked over floor, found a scorched bundle of cables

Main RCD tripping randomly, householder said blue flashes could be seen in the kitchen wall, found a choc block buried in plaster where builder had moved the cable

 

[securespark]

I wouldn't be happy with 1 meg if I were testing the circuit. I like to see at least 2 meg. However, with appliances disassociated from the circuit, I would expect the IR to be much higher.
I certainly would not accept those readings on a rewire.. They should be maximum readings on a newly installed circuit.

Go round again. Unplug (or switch off only if it has a switch and no socket) everything, then try again with the IR.

Edit, sorry Echo........

 

[deadshort]

Well, I would put my money on the boiler

DS

 

[seasickstevie]

Did he really say that he'd be "very happy with the readings [of 1 to 6MΩ] if it was a completely new rewire"?

That comment in itself would concern me.

 

[Lectrician]

Some electricians are great at install, but carp at fault finding. I hope he had all neutrals out in the CU for that RCD, MCBs off, and tested each circuit. Ooh, and the reading would of shot down when he decided to test the nail, not up.