Cooker Tripping RCD

[RAW1978]

Hi. I have a standalone electric cooker that is tripping the RCD (its a second-hand one but was tested and should be ok).

I've used the oven and hobs separately without a problem for a week.

Last night though the oven was on for at least half an hour without a problem, I turned a hob on to heat something and was still ok, after I turned a second hob on to heat something else the RCD tripped.

I turned it off and and turned the same back on after a minute and it tripped straight away again. I then left it for a few hours and tried all four hobs then plus the oven and it was ok (only left it on for 5 mins though).

The cooker is 7KW. The RCD for the cooker is 32A so even on max output it should be ok shouldn't it (7000W / 240V = 29.16A)?

The electrician who re-wired the house a few years ago was called (via our landlord) and said that the wiring was more than sufficient for any regular electric cooker.

Could it just be due to water on the hob plates from cooking maybe (I read that on a post on this site somewhere for a similar scenario)?

Any help / ideas appreciated...

 

[flameport]

If it is an RCD tripping (the device will have a test button on it), then one or more defective elements is the most likely cause.

Water spilled onto the hob won't in itself cause this as the plates should be sealed, however if a crack or other defect has occurred, water can get in and cause the problem you describe.

 

[Taylortwocities]

Please check what is tripping.
If it says B32 on it then you are looking at an MCB
if it says 30mA and has a test button then you are looking at an RCD
RCDs and MCBs do different things.

Here is how to tell#

Untitled

• Taylortwocities
• 27 Mar 2010
• 43

So lets start again.

What is it that is tripping?

 

[ericmark]

Elements in cookers are made with mineral insulation and the ends of the elements can never be sealed completely. The mineral insulation is hygroscopic so will draw in any moisture causing the RCD to trip. By heating the element the water will first cause more of a problem then it will be driven out. When cookers have got damp in storage often they need connecting to a non RCD supply to dry out and are then OK when used regular.

It was common not to fit RCD's to the cooker supply but in 2008 the regulations changed and wires buried at less than 50mm in a wall need RCD protection unless special cables are used. Ceramic hobs don't in general suffer in the same way as the older type elements and the oven element is more protected from damp. So modern cookers don't have the same problems to the older type.

There are ways to dry out a damp element but it can be dangerous. As a result I am not prepared to say how it is done. However most electricians will know and will be able to get the cooker running again.

Elements can of course go faulty as well as drawing in water. And the electrician will be able to work out if the element is faulty or just damp. This is not really a DIY job so likely you will need an electrician to correct it for you.

 

[RAW1978]

Hi all,

Thanks for the replies. It is definitely an RCD (30mA with test switch).

So far since then the cooker has been ok. Have used it two or three times since without an issue.

The only difference is that the cooker was on for such a long time when it did trip, something I haven't needed to do since (yet).

Is it possible that there is a tiny earth leak that only trips the RCD after a considerable amount of time being on? I had heard they were so sensitive that they trip after any leak at all?

Each individual component (oven / grill / 4 x hobs) seem to work fine so the elements seem ok?

Am I ok to continue to use or should I have an electrician in to check it out? I could do without the cost but will do so if you feel it is necessary.

 

[Taylortwocities]

Elements in cookers are made with mineral insulation and the ends of the elements can never be sealed completely. The mineral insulation is hygroscopic so will draw in any moisture causing the RCD to trip. By heating the element the water will first cause more of a problem then it will be driven out. When cookers have got damp in storage often they need connecting to a non RCD supply to dry out and are then OK when used regular.

.

Eric has said the correct bit here. It looks like damp was the problem and it has now been driven out - you are probably Ok from here.
I would just keep an eye on it and consider getting it checked out if the problem happens again, with the cooker in regular use.

 

[RAW1978]

Ok will do...thanks to all for the help and advice.

Cheers