I'm after a bit of advice.....

I moved into a flat last week, and the cooker has tripped the RCD switch on half a dozen occasions. All but one times, resetting the RCD switch has resolved the problem and the cooker has worked ok, but on the other occasion, it kept tripping, although it has worked since.

The landlord has had an electrician out to look at it, and his solution was to move the Cooker in the fuse box, so that it is not covered by the RCD. He said cookers have a large leakage and trigger the RCD too easily.

I'm worried that this has removed the symptom but not the cause of the problem. Is this sound practice. Is it ok under UK regulations to do this?

I know this isn't necessarily the forum I should be asking this question on, but any replies would be gratefully appreciated.

Thank you

My first question would be What is the rating of the RCD? 30mA 0r 300mA?
My second question would be what type of cooker is it- what type of cooking elements?
It is true that some older type cookers can accumulate moisture or damp in the elements IF not used for a long period of time, thereby tripping the RCD. If that would be the fault, then the remedy would be to put the cooker on maximum to evaporate the moisture. If the RCD is still tripping, thaen there is a serious fault. Having said that, I would still try and search the problem. It is most probably a wire inside the cooker which has melted from the heat.

[This message has been edited by Belgian (edited 07-09-2003).]

Half a dozen times in a week? And it is the cooker that is causing problems all on it's own? If this problem arose even if you were using one or two rings, something's wrong.

Hi there spc,

Basically, for the RCD to trip it means that current is leaking to earth somewhere that it shouldn't.

It could be faulty wiring, as mentioned already, or it could be an element which is on its last legs. The heating elements sometimes go quite leaky after a few years and cause what appears to be random tripping. Sometimes the insulation within the element can break down so that a short occurs when the element gets hots.

Another possibility is that grease has gotten into a terminal block somewhere under the hob and is causing the tripping -- I've seen that on several occasions.

The electrician who came out should have been able to perform an insulation test on the cooker -- Basically a high-voltage test to see where the leakage is taking place.

As for rewiring so that the cooker is not fed through the RCD, whether this is acceptable or not depends upon the way in which your flat is earthed.

It is allowable with some types of earthing system, so long as certain provisions are met, but if your flat's earth is just to a local ground rod then it will most certainly not be permissible.

Hi. Thanks for your replies.

The RCD is 30mA. The guy who came out said really cookers shouldn't be covered by the RCD as this value can be too low, and can be tripped too easily. Is this true?

The RCD has tripped when turning on the cooker, and on one occasion, its ventilation fan above it. On the day when the RCD repeatedly tripped, it was by turning on the oven; it was ok at temperatures below 100 degrees, but as soon as I turned the knob beyond that, the RCD tripped.

The cooker, hob, and ventilation fan, are all on the same wiring; switching off the cooker fuse in the fuse box stopped all three from working. That's the only test the guy did when he came; he didn't look at the cooker or do any tests on it.

He said it was safe to move the cooker outside of the scope of the RCD because the wiring was still covered by a fuse in the kitchen above the cooker, and the main switch in the fuse box.

I guess what I really want to know, is, is it safe to carry on using the cooker like he said, or should I stop now and get out somebody to look at the applicance. It has worked fine since, but of course, it is no longer able to trip the RCD.

Thanks

There's a clue that he wasn't too bothered about what's really wrong.

It could be a bad element on the oven, or it could even be a neutral-to-earth short somewhere in the unit or wiring (this can lead to all sorts of apparently random tripping, depending upon what else is turned on at the time).

I'd suggest that you get somebody else out to check it over.

Thanks again.

Are there any circumstances where the oven may trip it, but there isn't actually a fault?

spc

Do this electrician a favour.Do not use the cooker untill you have it tested by a professional. You see people can postulate all they like aboult what is wrong with the cooker but the fact is that any protection against electric shock that you may have had via the RCD is now no longer available!
Pauls comments are spot on but if you are electrocuted (God forbid!), this poor electrician will be hauled before the courts to give account.Too late then eh? Poor guy will never be able to hold his head up again when among other competent electricians!

Since my last message I've had someone out to test the cooker and he replaced the element.

The cooker's working fine, but is still outside of the RCD protection.

However, last night the extractor fan above the cooker, tripped the RCD switch when it was turned on, but has been ok since.

Could this be linked to the cooker problem, or is the fan possibly faulty. The fan, hob and cooker are covered by the cooker switch in the kitchen, but the fan is outside of the cooker circuit breaker in the fuse box.

The guys the landlord sends seem to be either experts in electrics or appliances, but not both. I'm wondering which one is best to go back to, to sort this out.

Let me se if I've understood this correctly. Are you saying that turning off the cooker switch on the wall shuts off the hob, oven, and the fan, but if you turn off the cooker circuit-breaker the fan still runs?

If so, then you definitely have some crossed wiring. It sounds as though the fan is getting its "live" feed from another circuit, but its neutral is wired back through the cooker panel. I expect you'll find that turning off some other circuit breaker stops the fan from working.

This really needs to be sorted out, as apart from causing nuisance tripping there is a safety aspect in that crossed circuits can result in someone turning off an isolation switch and the circuit not being dead.

Over here, ranges are exempt from RCD protection, mainly because of this Leakage current problem.
It's the same for Refrigerators,Hot Water Cylinders and Air Conditioning equipment.
With respect to ranges though, I'm not sure if it was mentioned above, but due to the heating and cooling cycles within the range body itself, during operation, there will tend to be a small, but appreciable build-up of moisture, that can slightly alter the Insulation Resistance values of the appliance, this is normal and any range that has a Minature Circuit Breaker protecting it(at the switchboard), should be fine.

[This message has been edited by Trumpy (edited 07-17-2003).]

Trumpy,
Ranges aren't specifically required to be on an RCD-protected circuit here, so long as the loop impedance and protective device(s) can meet the specified 5-second disconnect time on an earth fault.

In practice, that usually means that where the earthing system is TN-S or TN-C-S (PME, equivalent to your MEN) then an RCD is not necessary. If the TT system is employed, then the RCD becomes essential for all circuits.