Extending 10mm mains circuits. How?


Postby Hopeless_at_DIY » Thu Apr 21, 2011 3:50 pm

My wife insisted that when we bought our new cooker, it had to be a "range". This means I need to move the cooker switch along the wall as otherwise it will be placed directly above the cooker, which is obviously not desirable.

Unfortunately - there isn't enough play in the existing mains cable to reach the new position. I would dearly like to avoid chasing the cable back through to the consumer board and replacing the whole length. Can I use a 30amp junction box to join two 10mm mains circuit cables together without anything bursting into flames? The additional length I need to add on is less than half a metre. :?

Just to clarify...
- The junction box will remain easily accessible to comply with regs
- The cooker is rated 32kw "minimum"
- The cooker switch and connection block are all 45 amp rated
- I'm planning to run 6mm cable from the connection block to the cooker
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Postby collectors » Fri Apr 22, 2011 7:19 am

Please get a qualified electrician to do this.

1. No! you cant join 10mm cable using a 30 connection as 10mm is rated at 53 amps.
2. No! you cant use 6mm to connect the cooker.
3. I based this on your suggestion that the cooker is 32kw = 133 amps (Dont think so)
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Postby ericmark » Fri Apr 22, 2011 7:31 am

Any junction box has to be assessable for maintenance. So you want something looking neat. What I would suggest is a cooker connection unit these have the terminals size you need and look neat. It will also comply with showing where cables run. Although still can be damaged in a large fire it will be durable enough to suit the purpose.
In a domestic Part P will apply of course.
As to cable size this is selected to match the MCB size and for flex rated 90 degs 6mm is rated 55A but cable rated 60 degrees which is more normal is rated 39A so care is required when selecting cable.
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Postby ericmark » Fri Apr 22, 2011 11:20 am

[quote="collectors"]Please get a qualified electrician to do this.

1. No! you cant join 10mm cable using a 30 connection as 10mm is rated at 53 amps.
2. No! you cant use 6mm to connect the cooker.
3. I based this on your suggestion that the cooker is 32kw = 133 amps (Dont think so)[/quote]
I did at first think 6mm flex would not comply. However before posting I looked up the rating in the BRB and realised if 90 deg cable is used it would comply.

I think it is a fine balance as we know most people will go ahead what ever we say so better to give a way to safely do the work rather then saying just don't do it. You will see in many of my posts how I point out by time they pay the LABC their fees and hire the test equipment required likely DIY will cost more than getting a registered electrician to do the work.

I was rather surprised when I got my new cooker. Rings 4 of at between 2.7 and 3.7kW with an oven having 3 elements top bottom and back (fan). Plus a top oven/grill which must when all added up exceed 32A by quite a margin. However the Maker "Belling" says supply with a 32A supply. I will suspect as with old baby belling there is some switching to stop overload.

The BRB says follow manufactures instructions so if they say 32A then 32A it is.

Clearly the poster can't read as 32kW = 139A and I don't think any domestic cooker will need that? So I assume it is 32A which is required.
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Postby RICHARD MASON » Fri Sep 27, 2013 12:47 am

its a calculation called DIVERISTY that has to be applied to current loadings of this nature and demand.
32kw = 139.13amperes [@230volt] take the 1st 10amperes which leaves 129amperes then add 30% of the remainder thus: 38.7 amps plus 10 amps = a total of 48.7amperes if a socket outlet is integrated within the cooker control switch you must add an additional 5amperes to your total current demand.- 53.7amperes :-)

But a 32ampere supply maximum will be adequate because your stated current demand is a guess and not the actual total current demand stated on the rating plate
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Postby ericmark » Fri Sep 27, 2013 2:44 pm

I would hope that after 2.5 years this would have been sorted.
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