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Help with range cooker please

Postby tsb » Wed May 19, 2010 4:38 pm

My new dual fuel range cooker is tripping the RCD when I turn any of the ovens on. Its not tripping the MCB. Previously there's been a gas oven in its place, so there has never been any appliance connected to this circuit. The techy bits I can tell you are.... Its a 32amp MCB. 6mm cable to the cooker switch which is a 45amp switch with a 13amp socket. The spec on the cooker says max electrical load at 230V is 8.7KW.

I connected the cooker up today. When I first turned the ovens on, everything worked but once switched off and then back on again that is when it started tripping out.

Any advice what the problem might be would be appreciated.
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Postby ericmark » Thu May 20, 2010 10:31 am

The elements will attract water from the atmosphere and as they warm up they will allow enough leakages to trip the RCD. As they get hotter they will drive out the moisture and will likely be OK again.

Because of this many manufactures recommended not having a RCD for cookers but the new rules requiring RCD for buried cables in walls has resulted in that no longer being an option and manufactures may need to re-think.

If the cooker has been in storage then this may be the problem and heating up the cooker once may cure it.

However the method used to heat up the cooker once to drive the water out is very dangerous and I am not prepared to detail how it's done on here sorry.
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Postby jimmy_one_ball » Fri Jun 25, 2010 10:44 pm

Alternatively, you may have an earth leak, may be worth getting the conductors to the appliance tested and the appliance FAT tested.
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Postby ericmark » Sun Jun 27, 2010 5:41 pm

[quote="jimmy_one_ball"]Alternatively, you may have an earth leak, may be worth getting the conductors to the appliance tested and the appliance FAT tested.[/quote]
I am sure they do have an earth leakage. There are tests that can be done of course they all come under "Inspection and testing of in-service electrical appliances" which has a number of sub-sections Hand held, Portable, Movable, Stationary, Fixed, Appliances/equipment for building in, and Information technology equipment (business equipment) and they all are subjected to same tests. However on items over 3Kw the clamp on ammeter required to measure the milli-amp leakage to earth is expensive and often not used and the appliance is normally part dismantled to complete the tests using a insulation tester. This of course is a problem where the item has some guarantee as a third party can hardly dismantle to test.

Normally the site electrician will test the installation which will include testing the RCD which is done in 6 parts 2 to show it will not fail at 15ma and 2 to show it will fail at 30ma and 2 to show it will fail in 40ms at 150ma and if it passes and the cooker trips the supply it is simply a matter of sending the cooker back as faulty.

However as already explained there is a typical fault which can be rectified on site and some suppliers are really sneaky and they know if the cooker is powered up without a RCD it will drive out the moisture so they do just that. Then claim there was nothing wrong in first place and try to charge the customer.

To save all this hassle most electrician will cheat using one of a number of methods and get every element hot on site for a couple on minutes and try drying it out on site before returning it.

However it is cheating and I am not prepared to detail how it is done. The appliance testing is often split into two that which can be done with a all in one tester (PAT) and that which needs the skill of the electrician to test it. But to as you put it "FAT" (Fixed appliance testing) may prove the appliance is faulty but it will not repair the appliance and the only advantage would be you can prove it was faulty.

And a range cooker is a heavy beast and really the best option has to be for some one "Often refereed to as their engineer" to do a site visit to test and if possible correct the fault and there is very little the DIY person can do himself.

Both as the DIY person with not have the meters or the expertise required. I am not being sneaky by not saying how it is done as I am sure if I did the moderators I would hope would delete it anyway. It is just not a DIY job.
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