RCD - Cooker

[highspark]

Just fitted a cooker as soon as energised RCD triped. All wiring correct etc.

Tenant says had a few problems with intermittent tripping.

Old cooker was gas with ignition plugged into 13A socket fed from old electrical oven circuit 6mm cable. I have utilised this.

Did I/R Test on circuit. Live-neutral >500, Live-Earth >500. Neutral-Earth 1.45m ohms.

Ramped RCD at 33ma

1/2 timer IdeltaN - Trip 0'00ms

Faulty RCD yes.

But faulty circuit aswell? Under 2mohm

 

[jpm646]

Did u disconnect the neutral and earth from the board as it might be reading through other circuits or if it's a PME system it will show as a fault (I would expect it to be lower than that though if it was PME)

 

[highspark]

The oven light came on fine as soon as the oven was switched on it tripped. And yes you could bd correct I did mot disconnect between circuits just bar to bar.

 

[jpm646]

Could b RCD but only under load as the light might not be enough to trip the RCD also does it trip when u turn on the hob or grill, could b a faulty cooker element?

 

[highspark]

As soon as the hob is switched on it trips mate.

 

[Spazz]

I had this the other week after changing the CU.

Is the cooker plugged into a socket using a 13A plug?
If it is try changing the socket, it worked with me - the socket was providing a small earth leakage when the cooker was plugged into it - changed socket and no earth leakage at all.

 

[Spazz]

Do a pat test on the cooker otherwise - N&L-E using 250v setting

 

[highspark]

Is it safe to IR a cooker at 250v

 

[Spazz]

it should be - cookers operate at 250v AC so should be fine to IR at 250DC.
Even if there is a transformer in there is will still reduce it to the same voltage as the circuits operate at.

If in doubt IR at 100v DC if your IR Tester has that

 

[Strima]

If there was previous intermittent tripping it points to leakage on other circuits and the latest addition tipping it over the edge. Have you tried it with other circuits isolated?

 

[highspark]

Quick one - tenant just phoned said rcd won't go up at all now even when all circuits isolated.

I told him to flick switch in the off position on cooker switch and RCD restored. With no power going to it at all? Crazy?

 

[Spazz]

You have an earth leakage on the cooker supply.

Disconnect the cooker and check the IR of L-E & N-E. Make sure you disconnect the cooker circuit from the board when testing.

If you have below 5MOhms think about replacing the circuit cable, below 2MOhms replace it 100%

 

[highspark]

If the circuit is isolated (via mcb) but still connected inside fuseboard how can there be an earth leakage from that circuit?

When the cooker switch was in the on position it is tripping rcd and not resetting but in the off position it would reset.

I did an IR as above in previous posts and got a low reading of 1.45mohns but this was bar to bar. So as said possibly reading through other circuits

 

[Spazz]

but remember 1/R1 + 1/R2 + 1/R3, etc

Getting a result of 1.45MOhms you could have a load of very high readings and 1 very low reading.

But that tells me that all are above 1MOhm so that should be ok.

Try turning the cooker isolator on and disconnecting the cooker circuit from CU and the cooker from the circuit. If you get a high reading put a plug into the socket (just a blank plug with no cable) and do it again - I have had several dodgy sockets lately, some new and which have been on installations for years, but no problems because no RCD installed.

 

[highspark]

No socket on this one. Just a single cooker switch. Head is baffled