I have a problem with the rcd tripping when the grill or small oven is switched on. I have checked the elements with a meter and they appear not to be breaking down to earth. I have found that it trips if the thermostat is off, which disconnects the neutral to small oven and grill elements, when the grill/oven switch is turned on. Could this be a capacitive spike to earth causing the tripping as it does not trip if the thermostat is on to give the elements their neutral before the live is switched on and if so how to I overcome the problem?
grill trips rcd
- Thread starter billtc
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Only an IR tester will tell you the true value of resistance to earth.
The thermostat should be on the live, not the neutral side of the element..
Thats true but I can't believe all 3 elements are faulty as I have managed to trip the rcd with each element with the other 2 disconnected
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I was surprised but the "Whirlpool" cooker is wired with the blue from the neutral input to the thermostat and then on in black to feed all neutral feeds for the small cooker elements and neons. Obviously designed like that but I was surprised like you.
Under the 16th Edition we were advised that under normal circumstances a cooker should not be connected via an RCD because the elements were known to trip RCD at switch on as a result of water penetration into the elements.
Under the 17th Edition we of course have to connect via an RCD.
What is the insulation resistance of the elements after say 12hrs or more after use and relatively soon after use?
Also does the RCD trip only at switch on, or also when the thermostat turns off?
Under the 17th Edition we of course have to connect via an RCD.
What is the insulation resistance of the elements after say 12hrs or more after use and relatively soon after use?
Also does the RCD trip only at switch on, or also when the thermostat turns off?
i somewhat agree, but an IR tester will confirm this and the cable to the oven can then also be IR tested as its possible there is an NE fault on this (or even another circuit)
I would suggest putting it on its own RCBO, so that the leakage isn’t accumulated with other leaky devices such as computers.
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As already pointed out cooker elements are hydroscopic and as the elements warm up the water moves and the leakage can increase before it drives the water out.
I have in the past where the cooker has been in storage and likely only to require a one off drying out to cheat keeping everyone away from the cooker while it heated up one time then reconnected and all has worked. Not saying what I did as sure any electrician can work it out and I don’t want DIY’er copying.
As to not being on earth leakage that is an option but would require a rewire in ali-tube “Guardian” or “Flexishield” etc.
There is nothing in the 17th Edition that says cookers must have an earth leakage device only that non protected cables can’t be used without a RCD.
I can see how this can apply to new installations but not how one can know what cables or routes have been used in the past in my house only the final run down the kitchen wall falls foul of 50mm rule it goes up through cavity not permitted now I know but was when house was built so one straight length of conduit in kitchen would allow non RCD supply to cooker. But my cooker now 25 years old has never tripped the RCD. Only the oven and grill have mineral insulated elements the hobs being ceramic. And the 10ma limit before extra earths are required should not trip a 30ma trip anyway and although we know there is a problem using non RCD protected circuits to cure it would also point to over 10ma leakage and we should earth as required under the 17th Edition for high earth leakage so I am not convinced as to the benefits of non RCD protected supplies and would blame pour design on the cooker manufactures part.
And a new cooker may cost less than re-wire food for thought???
Eric
I have in the past where the cooker has been in storage and likely only to require a one off drying out to cheat keeping everyone away from the cooker while it heated up one time then reconnected and all has worked. Not saying what I did as sure any electrician can work it out and I don’t want DIY’er copying.
As to not being on earth leakage that is an option but would require a rewire in ali-tube “Guardian” or “Flexishield” etc.
There is nothing in the 17th Edition that says cookers must have an earth leakage device only that non protected cables can’t be used without a RCD.
I can see how this can apply to new installations but not how one can know what cables or routes have been used in the past in my house only the final run down the kitchen wall falls foul of 50mm rule it goes up through cavity not permitted now I know but was when house was built so one straight length of conduit in kitchen would allow non RCD supply to cooker. But my cooker now 25 years old has never tripped the RCD. Only the oven and grill have mineral insulated elements the hobs being ceramic. And the 10ma limit before extra earths are required should not trip a 30ma trip anyway and although we know there is a problem using non RCD protected circuits to cure it would also point to over 10ma leakage and we should earth as required under the 17th Edition for high earth leakage so I am not convinced as to the benefits of non RCD protected supplies and would blame pour design on the cooker manufactures part.
And a new cooker may cost less than re-wire food for thought???
Eric
Thanks for info & yes I have made it trip when the thermostat switches off. So to confirm any of 3 elements fed on their own, by disconnecting the others, can trip with the thermostat off ( ie no neutral to element ) when the live is connected and also with the live connected and the thermostat switches off to disconnect the nuetral first.
I can confirm the neutral from the thermostat also feeds the 3 elements
If the problem were that the elements had become hygroscopic, then as they heated up (while the stat was closed) the water would be driven out, and consequently there should be no fault when the thermostat opened again (which we now know is not true). At the same time, if it was a problem with the elements passing current to earth, then the problem would exist if the thermostat was open or closed.
I am therefore beginning to think that there is some other fault. Could the thermostat itself have a fault in that it has earth leakage when in the open position? Is there some other circuit that becomes active when the thermostat switches off? Maybe an indicator light
In the first instance I would be tempted to conduct an experiment replacing the thermostat with a normal switch (taking all safety precautions including making absolutely sure that the oven did not overheat!!!) This would either identify or eliminate the thermostat as the source of the problem.
On re-reading this I think I should clarify that the experiment should only be for a few minutes. I did not mean this as a permanent or even semi permanent solution!!!
I am therefore beginning to think that there is some other fault. Could the thermostat itself have a fault in that it has earth leakage when in the open position? Is there some other circuit that becomes active when the thermostat switches off? Maybe an indicator light
In the first instance I would be tempted to conduct an experiment replacing the thermostat with a normal switch (taking all safety precautions including making absolutely sure that the oven did not overheat!!!) This would either identify or eliminate the thermostat as the source of the problem.
On re-reading this I think I should clarify that the experiment should only be for a few minutes. I did not mean this as a permanent or even semi permanent solution!!!
Yes it will feed the elements, but it is not switched, it goes to the t/stat as & is there as a junction only.
No it definately feeds the neutral to the elements and neons via the thermostat with a change of colour from blue to black either side of the stat contacts. Seems wrong to me that you switch the neutral but thats how its wired so it is how it was designed by Whirlpool.
As evrything works ok if the thermostat contacts are closed before the live is connected I suspect that the elements are probably ok. I still think it may be capacitance causing the rcd to trip so possibly the rcd has become too sensitive and perhaps this should be checked.Do rcd operating values change ?
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