new cooker tripping main rcb


Postby basey » Sat May 19, 2007 12:16 pm

I have just had a 900mm range cooker delivered it is a single oven and gas hob. when plugged in through a 30amp cooker socket it recieves electric as lights etc work but as soon as the oven is turned on it trips the main house circuit breaker (not the cooker supply rcb). when testing the socket it runs a kettle or other item no problem. I have an engineer on monday from smeg to check the new oven but is it something wrong with my supply/earthing ?
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Postby Jeffmo » Sat May 19, 2007 5:44 pm

Hi sounds to me like it could be your cable sizing , check the cooker output and get back to the forum also see what size the cable from switch to fuse box / consumer unit is .Regards Jeff
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Postby sparx » Sat May 19, 2007 7:41 pm

Hi, as circuit mcb does not trip but apparently the main RCD trips then indicates an earth fault on oven, was flex/ plug already connected to oven ie moulded on plug or has it been fitted there? Anyway as light works ok it points to either damp in oven element or loose connection on oven, don't think house supply at fault, regards SPARX
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Postby basey » Tue May 22, 2007 8:52 pm

thanks sparx the engineer attended and after 1/2 hour found a frayed wire which was touching the cooker body. shows my earth trip was working well ! Not sure how it got frayed in a brand new cooker but still easily fixed.
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Postby Obbzi » Thu May 24, 2007 8:14 am

I am having a similair problem :cry: Just had a new kitchen fitted with a double oven, when we turned the smaller oven on fine, when we turned main oven on, oven switch tripped out in fuse box , reset the trip and had both ovens running together fine. Tried to turn the main oven on the other day and it tripped the oven switch in the fuse box again and it can't be reset :cry:

Kitchen fitter installed 10mm cable from oven to oven isolation switch in kitchen and the mains box has a 30amp trip thing.

Any ideas? :cry: :cry:
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Postby pdenni » Thu May 24, 2007 7:02 pm

hi obbzi

30 amp breaker seems a little too small for that oven if you have the instructions tell me what the kw rating of the oven is and i will work it out for you
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Postby Jeffmo » Thu May 24, 2007 8:42 pm

cookers are usually protected by a 30 amp fuse or mcb for a cooker rated at up to 12kw and a 45 amp fuse or 50 amp mcb is needed for a cooker rated at above 12kw.So initially check the rating of the cooker , i am a bit suspicious about the fuse rating , reason being 30 amp really only needs 6mm cable up to 20 metres and 10mm cable if the run is between 20 and 30 m , i have a feeling that the protection is too small . Another possible is inside the cooker connection box or cooker switch there is a loose connection . If the switch incorporates a 13amp socket opening then they are notorious for loose conns , due to the amount of cable chucked in the back of them , especially with the larger cables from 10 mm up . Remember though please be very safety concious if your having a look . I think for someone whose not sure its best to get someone in .Hope this helps , you will probably get a reply from my guru of electricity Mr Sparks as well , he is the man so listen good . Good luck Jeff
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Postby pdenni » Thu May 24, 2007 9:35 pm

hi jeffmo

dont mean to be picky but the calculation for 12kw without cable length or diversity is 52 amps.
7.5kw is pretty much the most you could put on a 32amp breaker
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Postby sparx » Fri May 25, 2007 3:44 pm

For Jeffmo; thanx for compliment but won't get involved in this one, enough experts here already!
BCNU SPARX
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Postby Jeffmo » Fri May 25, 2007 6:14 pm

Hi Sparks , ok obviously my estimate is without diversity or cable length , but as a rough estimate i think my calc are correct ,assuming a little diversity ,very little cos it should be on seperate circuit and assuming cable length . I'll leave the confussion for questioners to others from now on . was just tryin to keep it simple .Cheers Jeff
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Postby Jeffmo » Fri May 25, 2007 7:09 pm

Basic calc as i know it : example =
12.5 kw = Total current = P/U = 12500/240 = 52.08A
The demand = the first 10A = 10+ 30% of remainder =
30 x ( 52.08 - 10)/100 = 30 x 42.08 /100 = 12.624
Plus allowance for socket outlet if fitted =5A hence answer of 10+ 12.264+5 = 27.264 therefore 30 amp protection will do , dependent on length of run ok ive said my peace thankyou .
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