Earth trips on RCD when cooker switch on


Postby dcjones » Tue May 20, 2008 7:20 am

New consumer unit fitted with 40 A MCB for cooker on a 12 way split unit double pole and RCD rated at 63A 30mA.
When cooker switch on one ring works for approx 1 min - RCD trips. Switch two on and the RCD trips immediatel.
Switch oven on RCD trips immediately.
Switch on middle oven/grill - RCD trips immediately.
With power switch on and digital clock displayed, nothing trips.

No other faults with any other circuits in the house.

Also the RCD does not trip when test button pressed.

Advise and suggested rectification apprecaite asap. There are only so many micro-waves meals I can take.
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Postby ericmark » Tue May 20, 2008 2:22 pm

There are two possible causes.
1) RCD or wiring faulty unlikely as runs for 1 minuet with ring.
2) The Cooker see below.
Cookers with mineral insulated elements will absorb moisture this moisture can cause RCD’s to trip. Traditionally cookers were not supplied through the RCD because of this problem. Those with ceramic hobs all three types do not have a problem, one because they don’t use mineral insulation and two because liquid is unlikely to reach the element or induction unit. Ovens although normally fitted with mineral insulated elements are less prone to the problem.
There are two cures.
Repair or change the cooker.
Supply from non RCD protected side of consumer unit.
Until the 1st July you are allowed to supply from the non RCD side so long as there are no sockets which are likely to be used to power items outside.
After the 1st July then the cable would need to be one of the specials if buried in a wall i.e. Flexishield not twin and earth.
Sometimes one can dry out cookers for example when this happens after returning from holiday and as long as they are used frequently they will work OK but heating elements can never be completely sealed and they are hydrophilic so will absorb water from the atmosphere.
I suggest to contact who ever changed your consumer unit and ask their advice. I have known faulty RCD’s even when the RCD tester shows them as being OK so normally we would change the RCD even if on a temporary basis to ensure it’s not faulty.
I will not explain how to dry out cooker on here as the method I use is dangerous but I am sure your electrician will know the same tricks as me and will try drying it out.
As with the changing of the Consumer unit it is not really a DIY job. He will use special meters to test RCD and to test your cooker and the meters cost more than a new cooker so this is why I say not a DIY job.
ericmark

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