Electric Oven tripping rcd

[sajeel]

Hi people,

Need your advice recently wired an electric oven onto new twin rcd board.
Oven was working on previous rcd and was recently purchased about a week a go. Was working fine on old type cartridge fuse board [emoji33] .
When I did insulation reading it would fail when I turn isolator on and test. So I checked all the wiring, removed oven and tested on a temporary plug and no tripping occurred.

Connection is fuse board to double pole isolator with 6mm to outlet plate and then oven.

I then removed isolator and placed connector block I got readings of around 35mega ohms on 250v.
After which I found the neon on the on side of isolator was causing ir fail removed and tested all passed ir so connected to 40a breaker as soon as isolator is turned on the rcd trips even before the oven is switched on.

Then an rcd ramp test was performed and was satisfactory.

My suspicion are 40a mcb or double pole isolator open to suggestions or further tests ?

Have I missed anything ?

 

[Octopus]

Replace the cooker isolator?

 

[Lucien Nunes]

When I did insulation reading it would fail when I turn isolator on and test

What were the readings?

neon on the on side of isolator was causing ir fail

All neons will give low reading L-N because above 90V they light and behave as a small load. But not L-E or N-E, so should not influence RCD tripping problem. Or do you mean the neon was causing low IR L-E?

My suspicion are 40a mcb

How would a faulty MCB cause an RCD to trip and why would it not then trip with the isolator off?

Post the IR values for the oven L-E and N-E. Cooker elements are notorious for causing leakage and RCD tripping, isolators are not, so I would suspect the oven first. It is possible that a relay inside is only putting the element in circuit when its supply is live, in which case it passes the IR test as the relay is open at that time.

Have you got a leakage clamp or a PAT tester that does full voltage leakage tests?

 

[sajeel]

Hi people quick update replaced double pole isolator and trip has disappeared it appears the switch must have been leaking voltage.

The ir readings were at 250v:
Switch closed: >300
Switch open: 0.027
After neon removed: 16

 

[sajeel]

I am aware ovens are notorious for leaks but the oven would have leaked when I plugged into to socket to test and tripped that circuit out also oven is new however I know that means nothing as double pole isolator was brand new as well.

 

[Lucien Nunes]

It would be interesting to see what was wrong inside the isolator.

Switch closed: >300
Switch open: 0.027

Are these results L-E, N-E or what? If they are megohms (always state the units!) L-E they don't give any clues the the specific fault, because the insulation is good when closed and you said the RCD tripped when closed but not when open. Even when open, 0.027 megohms shouldn't trip an RCD.

Perhaps there's some debris inside that moves whenever the switch is operated, or a flashover occurs at a peak voltage slightly over 250V. BTW have you tested at 500V?

 

[sajeel]

Yes did test at 500 have edited last post

 

[sajeel]

Hi people quick update replaced double pole isolator and trip has disappeared it appears the switch must have been leaking voltage.

The ir readings were at 250v:
Switch closed: >300 mega ohms
Switch open: 0.027 mega ohms
After neon removed: 16 mega ohms[

Thanks for all you help /QUOTE]

Hi people quick update replaced double pole isolator and trip has disappeared it appears the switch must have been leaking voltage.

The ir readings were at 250v:
Switch closed: >300
Switch open: 0.027
After neon removed: 16