1

Daughter left the oven on full heat and our house's RCD tripped.

Strangely, after removing the oven light bulb, we are now able to use the hot plates!

However, switching the oven/grill selector switch still trips the RCD. I've tried the switch in all its positions - full grill, half grill, bottom element only, both grill and bottom element.

I even changed the lower oven element, but this has made no difference.

What should I try next?

Adding picture of incoming 3-phase supply - the oven/grill circuit is formed by the brown wire from phase 2 and the blue wire from phase 3.

incoming supply

1034 ohm thing

Improve this question
4
  • 3
    This is a problem with your oven, not with your daughter leaving it on full heat, which it should be able to manage without failure. If you have a multimeter and know how to use it, you should start testing the (disconnected from all power) oven for the ground fault. If not, you should either get a new oven or have an appliance repair professional take a look.
    – Ecnerwal
    Commented Jul 14, 2020 at 12:54
  • 2
    Wha do you mean by "after removing the oven light bulb, we are now able to use the hot plates!"? Were you able to use them before it was removed? Or, why do you expect them to be useless without the oven light bulb?
    – Daniel Griscom
    Commented Jul 14, 2020 at 13:08
  • 1
    O, I see I didn't explain that so well. After the first trip out turning on a hot plate would trip the RCD. Then I removed the oven light bulb and am now able to use the hot plates.
    – minisaurus
    Commented Jul 14, 2020 at 16:11
  • 1
    The resistance to ground may be fairly high, from memory RCD’s trip at 30 ma , 240v the resistance to ground could be 8,000 ohms probably less but it may not be a direct short 240/.03=8000 it will probably be lower so a 1k reading to ground could be your fault. But it is usually visible as damage.
    – Ed Beal
    Commented Jul 14, 2020 at 17:08

1 Answer 1

Reset to default
4

It sounds like the high heat damaged the wiring in the oven. The light bulb being removed would indicate that damaged wire is on the neutral side with it out if you try to turn it on and the rcd holds. The elements probably have a similar issue with damaged insulation.

If I was trying to find this wire damage I would look where the lamp and elements might be close to each other coming through a fitting.

I would look for wire that was overheated and you can probably repair it with high temp fixture wire most ovens use 12 gauge wire for each element but it needs to be high temp fixture wire or it will fail when the oven is heated for any length of time. I have seen some commercial ovens that used 10 awg 1 time I use high temp “spade” style quick disconnects when the elements have those type of connectors if they use bolt connections I still use high temp crimp rings , standard crimp fittings will not hold up to the heat and current and fail in a short amount of time. But luckily your RCD has prevented massive arcing and possibly a fire.

Improve this answer
11
  • I forgot to mention, the oven is 3 phase. The grill/oven circuit uses L2-L3. I measured resistance across L2-L3 at the (unplugged) plug. With the oven/grill off, resistance is 0. With the oven/grill on, resistance is 732 Ohm. Is this ok, or too high? If I turn on the thermostat, resistance drops to 51 Ohm. This is the case for all the components I've tested: L3 -> grill, L3 -> oven, L3 -> fan, L3 -> light - all 732 Ohm with thermostat off. L3 to the thermostat switch gives 794 Ohm. Could this be the problem?
    – minisaurus
    Commented Jul 15, 2020 at 12:59
  • At the (disconnected) wall socket I get no resistance readings for L2. L1 -> earth 78 Ohm; L3 -> earth 589 Ohm; L1 -> L3 665 Ohm. L2 -> L1, L2 -> L3, L2 -> earth - all zero Ohm.
    – minisaurus
    Commented Jul 15, 2020 at 13:03
  • 1
    So you have a hard short(s) on L1,L2,l3 to earth 78 ohms is probably the element resistance. I would open the back of the unit you may be able to see the damaged conductors. In high temp equipment I replace not repair. There is high temp tape but but it is really not for repairs once the insulation starts breaking down it is unsafe. The high temp tape is for insulating things like split bolts.
    – Ed Beal
    Commented Jul 15, 2020 at 13:49
  • I've come a little further - I can't see any damage, but I've got 1034 Ohm across a ceramic thing that lies between the thermostat hand control and the light - see image. Plus 732 Ohm across the fan motor. Are both these parts faulty?
    – minisaurus
    Commented Jul 15, 2020 at 14:14
  • 1
    That part looks like a high wattage resistor I see a 1k on the right if that is correct it would be 1000 ohms 1034 is good (usually 10 or 20% is good). 730 ohms sounds high across the motor leads of a fan I want to say under 100 maybe even 10 would be normal but high resistance on the coil would not cause a trip unless the coil windings have failed and are also grounding out, this is where we use a megger , a high voltage ohm meter measuring the coil to ground at 500v if below 30k it’s toast so the fan can be a possibility if you take it out of circuit and see if it trips would be my test
    – Ed Beal
    Commented Jul 15, 2020 at 14:36

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.