Gas Hob Electric Oven Cooker Issue (Nightmare)

[mapleford]

Hi All

Been called out to an issue a clients daughter has had for a while

Basically, when the earth pin on the cooker plug touches the earth on the socket (metal plates, so front or plugged in) the RCD trips. You can plug anything else in and the sockets work. With the gas bayonet unplugged the cooker no longer trips. Checked the cooker with a Megger and can't find an issue there with insulation and have continuity from earth pin on plug to gas bayonet. They have a combi boiler thats cross bonded and not tripping anything and have checked the bond on the gas, cleaned it up and followed it from meter to MET. Have checked the sockets and no probs there and have replaced the RCD from 1970's to nice modern one, The system is TNS. What am I missing.

BTW first time stumped in many years!

 

[SLIPSHOD & SLAPDASH]

Odd, have you tested checked the gas pipe at the bayonet, to L, N & E  ?

Although if its on a bayonet then its probably a rubber hose to the cooker ?

 

[SPECIAL LOCATION]

Is this a single oven plugged into a ring socket?  

or is it off a dedicated cooker circuit?

You say the oven is all tested ok...

have you actually tested IR on the supplying circuit?

What actual current does the RCD trip at (have you ramp tested it)

Is it a cumulative residual current build up where the cooker tips the balance?

Some cookers say not to connect via an RCD due to natural leakage issues.. 

:C

 

[SLIPSHOD & SLAPDASH]

I assumed it was a gas cooker, what is it mapleford, cooker, oven or hob and all gas or dual fuel ?

And it trips with just the earth pin touching, not L or N ?

 

[mapleford]

Hi

It's a dual fuel free standing cooker

You only have to touch the earth pin with the bayonet attached for it to trip

Checked with bayonet unplugged and cooker plugged in and no voltage between bayonet and gas pipe

 

[SPECIAL LOCATION]

Title says 'Gas Hob'   and  'Electric oven' 

Doh..

you answered while I was posting!!

So the cooker is NOT actually energised when it trips...

just having the earth joined up and gas pipe connected?

Is the boiler supplied from the same RCD that is tripping...

(assuming this is a dual RCD board?)

 

[SLIPSHOD & SLAPDASH]

I would test between gas pipe by bayonet and the socket the cooker is plugged into, both continuity  & voltage between L, N & E

That is between the socket and gas pipe

 

[ProDave]

I'm really confused.

It's a dual fuel free standing cooker, which usually means gas hobs and electric oven and grill.

I would expect the electric part of that to be hard wired into a cooker connection unit on it's own radial circuit.

Are you telling us, that in fact the electrical half of your free standing cooker is in fact just connected to a flex and plugged into a 13A socket? If so I would first check the ratings as I would be very surprised if oven and grill on at the same time is less than 13A

So you touch the earth pin of this plug to the metal front of your 13A socket and the RCD trips?

the fault must lie on the ring circuit.  If it's only the pin of the plug touching and the L and N pins are not inserted, then it can't possibly be introducing an imbalance to the ring final can it?

I would want that socket off and examined first. Does it do the same if plugged into a different socket (and not just the other one of a double socket)?

 

[mapleford]

Haven't checked the ratings yet as wanted to be able to get power to it first

Had socket front and cooker plate fronts off no issues and can plug anything else in to them

Trips rcd if touched on either

 

[SPECIAL LOCATION]

What were your Ze, Zs & IR readings for the circuit?

Sounds like a fault elsewhere on the installation that only becomes evident when introducing a lower resistance earth to the circuit... 

what happens if you connect a long lead earthed at the MET to the socket front?

 

[SLIPSHOD & SLAPDASH]

Is the cooker gas connection a  rubber hose.

 

[Rob_the_rich]

Is the cooker gas connection a  rubber hose.

Natural gas cooker hoses have a metal armour within, in a spiral I think. Pretty sure LPG ones are the same. So they would be continuous electrically.

Is the gas pipe buried in the floor? Or is it visible all the way back to the meter?

 

[mapleford]

Gas pipe under floor to meter, rubber hose with metal running through it.

House is pre first world war semi detached with floating wooden floors so air gap under, 

Downstairs is fully laminate floored so thats not coming up!

 

[roys]

I think Spec Loc is on the right track.

To me it sounds like the cooker circuit hose and it owns gas earth is the decent earth, so when that earth is introduced to the socket it provides the return fault path for the socket circuit which has a fault on it and a rubbish earth.

Of course I could be talking rubbish and misunderstood it.

It is a good one though.

 

[ProDave]

Here's my off the wall theory.

This is a flush flat plate socket with clip on metal cover.

The metal cover does not actually make contact to the earth terminal of the socket as it clips onto a plastic frame.

A design fault or a wiring fault means the N wire pokes through it's terminal and touches the metal front, leaving it connected to N

And of course then shorting E (via the cooker / gas hose) to N trips the RCD.

Well you have to admit it's one possibility unless anyone can suggest a better theory.   :coat

 

[mapleford]

Sorry,

flat plate not clip ons

 

[SPECIAL LOCATION]

Any answers to post #10  ??????

What were your Ze, Zs & IR readings for the circuit?

what happens if you connect a long lead earthed at the MET to the socket front?

 

[Doc Hudson]

Hi All

Been called out to an issue a clients daughter has had for a while

Basically, when the earth pin on the cooker plug touches the earth on the socket (metal plates, so front or plugged in) the RCD trips.

So is this a new oven that has never worked, or is it an existing oven that these fault symptoms have recently developed? 

Doc H.

 

[mapleford]

Sorry, haven't got back for ze,zs & ir yet

Old(ish) cooker, been doing it a while

Aiming to get back monday

 

[dmxr]

So you haven't actually done any testing on the socket circuit?

Sounds like you've got a n-e fault.