New Oven Installation Tripping RCD

[borzoi]

Some advice please. We have a persistent problem where the cooker circuit RCD trips consistently in the Consumer Unit. The trigger is when anything on the new cooker is switched on - even just an oven light. No other circuits in the house seem to have this problem and it occurs when absolutely everything else is turned off.

We are on the second cooker of the same make and model. Two different electricians have been in to attempt an install with the same problem. Neither could find a problem with the cooker circuit, having 'Megger' tested the wires, but pointed in the direction of a faulty appliance.

A specialist in the appliance tested the second one in place and could find no fault with the appliance itself, although he could not cure the RCD tripping problem. Naturally he disagreed with the electricans and blames the electrical circuit.

I am after a way forward please as it is foxing better brains than mine! And costing me a small fortune.

My thanks in advance.

 

[securespark]

Cooke circuit incorrectly connected at the board.

Is it an RCD for many circuits or RCBO or RCD just for the cooker?

 

[ericmark]

I would agree with securespark most likely is at the consumer unit some one has connected the neutral to the wrong neutral bar.

However what I can't understand is if that's the problem why two electricians have failed to find it.

There are some odd faults where for example a faulty toaster can caused the RCD to trip when the kettle is used this is caused by a neutral earth fault and leaving item plugged in even if not in use can result in the wrong item being blamed for the fault.

But your comment "even just an oven light" makes me think neutral connected to wrong neutral bar in the consumer unit. If using a twin RCD consumer unit this fault will often cause BOTH RCD's to trip together not just the one feeding the item.

 

[borzoi]

That was quick!

There is a specific RCD for the cooker circuit. The cooker circuit includes a socket as well as the hard-wired cooker part - a small appliance such as a phone charger does not trip the RCD when connected to the socket.

The main theory is then that we have a neutral connected to the wrong neutral bar in the consumer unit. I shall put this to the electrician.

 

[ericmark]

What happens when a larger item is plugged in? It needs to draw more than 30ma a table lamp or similar. Likely mobile phone charger is less than 30ma.

If a table lamp trips the RCD then yes it would seem neutral in wrong place but you say now "specific RCD" for cooker likely a RCBO and it would seem strange for anyone to get that wrong.

What niggles me is two electricians have walked away without curing which seems odd. Using an insulation tester, a RCD tester, and basic skills one would have expected any electrician to find the fault. So I suspect it's not that easy of a fault to find.

 

[securespark]

Please post some pictures of the RCD that is tripping.

We like pictures!

 

[borzoi]

Thank you for the replies. It will be another day before I can get photos of the offending RCD. Summarising:

Things to try:

(1) Table lamp or kettle in socket next to cooker.
(2) The electrican suggested 'borrowing' a known working cooker and trying it out on the cooker circuit. Probably easier said than done!
(3) Hard wiring something else in to the cooker circuit - kettle may be. Sounds a bit unsafe!

Theories:

(1) Neutral connected to the wrong neutral bar in the consumer unit.

Others I have heard:

(2) Some neutral to ground earthing problem.
(3) Some poor wiring in the cooker/socket area.
(4) Faulty RCD.

 

[flyingsparks]

I agree sounds like a neutral in the wrong bar. If it is that, then the two 'electricians' you have used are obviously not up to the job, as this is the most basic problem to diagnose and solve.

 

[mfarrow]

Also check neutral connections aren't swapped with earth at CCU or isolator. It would be a very basic mistake, though.

If it's an RCBO neutral swap in CU I'd expect the other circuit (like shower) not to work correctly either.

 

[flameport]

(2) Some neutral to ground earthing problem.
(3) Some poor wiring in the cooker/socket area.
(4) Faulty RCD.

2 - very likely, usually where the fixing screws for the switch or socket have damaged the cable as they were screwed in. Cable could have been damaged elsewhere when installed, by rats, other trades drilling into floors / walls / other.
3 - possible but surely would have been obvious.
4 - possible, but unlikely.

All of the above and the incorrect wiring at the consumer unit are simple faults which the standard basic tests would have identified in minutes.

(1) Table lamp or kettle in socket next to cooker.
(2) The electrican suggested 'borrowing' a known working cooker and trying it out on the cooker circuit. Probably easier said than done!
(3) Hard wiring something else in to the cooker circuit - kettle may be. Sounds a bit unsafe!.

1 - Fine, as simple and easy to to. Should not really be necessary though.
2 - Ridiculous. They were not an electrician.
3 - Could well be unsafe, and therefore not recommended.

The only other thing would be the switch/socket itself having some internal fault. This is very unlikely, and even if it was, would again be easy to identify with a couple of basic tests.

 

[borzoi]

A slight delay getting the photo together. It is attached but of poor quality - the light was poor. Text written on it is as follows:

Things to try:

(1) Table lamp or kettle in socket next to cooker.
(2) The electrican suggested 'borrowing' a known working cooker and trying it out on the cooker circuit. Probably easier said than done!
(3) Hard wiring something else in to the cooker circuit - kettle may be. Sounds a bit unsafe!

Theories:

(1) Neutral connected to the wrong neutral bar in the consumer unit.

Others I have heard:

(2) Some neutral to ground earthing problem.
(3) Some poor wiring in the cooker/socket area.
(4) Faulty RCD.

Read more: //www.diynot.com/forums/electrics/new-oven-installation-tripping-rcd.376743/#ixzz2fYkjh7Yf

British General
CUR6330
ln=63A
l[delta]n=30mA
lnc=6000A
Un=230v-50Hz
IEC/EN 61008-1

Update on things to try:

(1) Kettle in socket - 'control unit' I believe is the terminology. This worked fine. I unscrewed the control unit and plaster came adrift - the socket still worked afterwards.
(2) Borrowing a known working cooker. Not tried.
(3) Hard wiring something else in to the cooker circuit. Advised not to try.
(4) Manufacturer is going to supply a third appliance.
(5) I am inclined to try a 3rd electrician - briefing them on the problem before starting.

Theories:

(1) Neutral connected to the wrong neutral bar in the consumer unit. If there is a single cable from consumer unit to control unit and the kettle worked. Is this now an unlikely cause?
(2) Some neutral to ground earthing problem. Sounds plausible but isn't this most likely in the control unit to cooker wall point area?
(3) Some poor wiring in the control unit area. We have had work done to the kitchen and I am beginning to wonder if this has been tampered with.
(4) Faulty RCD. Sounds unlikely (?) as the kettle worked.
(5) Faulty appliance. Unlikely that two are at fault but then what happens if they have been in a warehouse for a long time before delivery? It was on offer so implication is that it is an end-of-line model.

 

[flameport]

If the kettle works, the fault is beyond that point, or in removing it from the wall you have temporarily removed the fault.

It's either the wiring to the cooker, the outlet plate if there is one, wiring between the switch and outlet plate, or the switch itself.

As before - any electrician could have located the fault in 5 minutes.

 

[borzoi]

We have now traced and fixed the problem. It was a loose neutral wire within the control unit. Once re-attached and the cooker re-connected all seemed to work fine.

My great thanks to all who posted here - the advice was very useful and it helped me understand the correct layout and eventual solution. In the event the problem was diagnosed with the help of a neighbour who had to hand the right tools. He was able to prise the control unit away from the wall whereas I had not been able to.

It just leaves employing another qualified electrician to check the connections for safety and issue a certificate...

 

[mfarrow]

I'm glad it's sorted; what special tools did your neighbour have that neither you nor the 2 electricians possessed? Usually a screwdriver will do!

Get your money back off the other two. Failing to check for security of connections is what leads to fires. I'm surprised we're even allowed screw terminals anymore, when three indepedant dimwits working on the same circuit failed to spot a loose connection.

 

[borzoi]

My neighbour had a good pair of pliers and the confidence to use a bit of brute force! The cooker itself needed a particular star screwdriver head.