Fan Oven caused Arcing and RCD didn't flip?

XavierCrow

Hi there,

Recently had an issue in a new apartment that seemingly came out of nowhere. Basically I was cooking some chips on a tray with tin-foil on it. About halfway through the cooking process, after flipping the chips I put the tray back into the oven, but one of the corners touched off the side of the oven. Suddenly it was as if someone was using an arc welder in there. After a few seconds of pant-wetting electric arcing, the oven died. Not sure what would've happened had I been holding the pan at the time, but I didn't get a shock anyway, thankfully.

Strange thing is, none of the switches on our fuse-box flipped off. Obviously I'll be contacting my landlord about it, but I was wondering what sort've things I should expect an electrician to do in this scenario to make sure everything's safe? The only other issue we've had is with signal noise being really loud in one room, a problem we think is related to a dimmer-switch the room adjacent. Not sure that's an indication of poor wiring?

Anyone ever had anything similar happen? I honestly had no idea it could!

Thanks!

meercat

you need to get this checked by a competent electrician

it may be just the element breaking and arching across the broken conductor
this may not cause your mcb to trip as there would be no earth short
probably need new element though


dimmers do tend to humm and cause interference also

2011

XavierCrow wrote: »

Hi there,

Recently had an issue in a new apartment that seemingly came out of nowhere. Basically I was cooking some chips on a tray with tin-foil on it. About halfway through the cooking process, after flipping the chips I put the tray back into the oven, but one of the corners touched off the side of the oven.

The corner of the tray striking the oven may have caused...

1) ...a live conductor within the oven to short against the metal casing of the oven causing a current to flow to earth.

2) ...a live conductor to short with a neutral conductor.

3) ...nothing, the element just happened to fail then.

Suddenly it was as if someone was using an arc welder in there. After a few seconds of pant-wetting electric arcing, the oven died.

You will probably find that the element or cable failed completely.

Not sure what would've happened had I been holding the pan at the time

Probably nothing, but there is a chance you may have received a shock.

Strange thing is, none of the switches on our fuse-box flipped off.

Typically an oven would be protected by an MCB or a fuse (in older installations). Ovens would not normally be fed by RCDs. Both fuses and MCBs are designed to operate when the current flowing through them exceeds a certain value (regardless of where the current is flowing). In your case although the current provided a dramatic light show it was not sufficient to cause the protective device to operate. So 30A current flowing through a 40A MCB due to a phase (live) to earth or phase to neutral fault would not case the MCB to operate (trip).

Obviously I'll be contacting my landlord about it, but I was wondering what sort've things I should expect an electrician to do in this scenario to make sure everything's safe?

It would be no harm at all.

The only other issue we've had is with signal noise being really loud in one room, a problem we think is related to a dimmer-switch the room adjacent.

Why do you think it is related to the dimmer switch? Does this noise only occur when the light is on? Is the dimmer supplying a light with a CFL lamp installed?

Not sure that's an indication of poor wiring?

Would require more information to answer that.

Anyone ever had anything similar happen? I honestly had no idea it could!

Thanks![/QUOTE]

XavierCrow

Hi folks, thanks for replying, that's helped relieve some concerns I've had.

Why do you think it is related to the dimmer switch? Does this noise only occur when the light is on?

My flat-mate was the one getting the problem (I haven't had the same thing happen) so he tested it. When fully on, there's a little noise. Fully off there's none but anywhere in between is really loud. Apparently it's not just that one light dimmer though, there are businesses downstairs to us and he gets signal noise during weekdays as well.

Is the dimmer supplying a light with a CFL lamp installed?

No, they're spot lights installed into the ceiling.

Thanks again!

2011

XavierCrow wrote: »

My flat-mate was the one getting the problem (I haven't had the same thing happen) so he tested it. When fully on, there's a little noise. Fully off there's none but anywhere in between is really loud. Apparently it's not just that one light dimmer though, there are businesses downstairs to us and he gets signal noise during weekdays as well.

Not necesserily dangerous. Cheap dimmers often make buzzing noises.
Ensure that it is not overloaded i.e. a 250VA dimmer switch should not be controlling to amore that 250W of lighting.

I would recommend MK dimmers. They cost more, but they work and do not buzz!

XavierCrow

Not necesserily dangerous. Cheap dimmers often make buzzing noises.
Ensure that it is not overloaded i.e. a 250VA dimmer switch should not be controlling to amore that 250W of lighting.

I would recommend MK dimmers. They cost more, but they work and do not buzz!

Nice! I'll let my flat-mate know about them. Expensive I guess, but as a once off investment that solves his problem indefinitely, probably worth it.

As for the load on the dimmer, I guess I'll talk to the electrician about that. Maybe he can tell what wattage the bulbs are from a glance, there's certainly enough of them to overload a 250VA in that case.

2011

XavierCrow wrote: »

Nice! I'll let my flat-mate know about them. Expensive I guess, but as a once off investment that solves his problem indefinitely, probably worth it.

+ 1

As for the load on the dimmer, I guess I'll talk to the electrician about that. Maybe he can tell what wattage the bulbs are from a glance, there's certainly enough of them to overload a 250VA in that case.

Yes, load on the dimmer, suitability of the dimmer etc are all best left to the electrician.

deandean

There's a good video in youknowwhere showing an oven element acting like an arc welder, so yup it happens...

http://www.youtube.com/watch?v=lHJI47jWuJ4

Bruthal

It can happen, and doesnt trip the MCB because a lot of the element impedence/resistance is in the circuit.

If its arcing in a fault half way along the element for example, the current flow could be double what the element would take when working normally, and this would definitely not trip a 32 amp MCB.

If it was arcing up beside the neutral connection to the element, then the arcing wold just be the elements normal operating current. Probably less likely to arc as much at that end though.

AN RCD would instantly trip of course, but they are not used on cookers, at present.