Cable size and live wire colour change

[Des 56]

Quote
MCB is rated 32A. THis is too high for 4mm cable.

?​

 

[Fleetwood]

Well 4mm cable has less current carrying capacity then 32A.

 

[kingeri]

Depends on the installation method.......4mm can carry 37amps if clipped direct or embedded directly in plaster. 4mm radials on 32a breakers are quite common, usually for socket circuits.

Your question seems to hinge on deciding what size cable you have, something which we can't answer remotely on a forum. Take a sample of it to the wholesaler or even to the big orange shed and compare it to 4mm and 6mm on sale there! Or post some to me and I'll tell you what it is! 4mm is a bit bigger than 2.5mm.....6mm is quite a bit bigger......as I said earlier sparks can usually tell the difference at a glance. You could measure one of the strands and calculate the csa that way, if you have the right equipment (a vernier caliper).

 

[Fleetwood]

So on that basis then we could connect the 10.5KW oven even if the cable is 4mm

 

[HandySparks]

Well 4mm cable has less current carrying capacity then 32A.

If clipped direct or buried in non thermally insulating wall, CCC is 37A. How is it installed?

(Edit: not quick enough!)

 

[kingeri]

After applying diversity, you're looking at just under 30a (without actually calculating it), but you say there is also a separate socket outlet. Have you checked the installation method along the whole length of the cable? Just be sure that it doesn't pass through insulation anywhere. Also remember that you may need to account for grouping.

It would be standard practice to use 6mm for this circuit.

Does the switch control the lower, separate socket outlet?

 

[kingeri]

Also, have you read the instructions to see what size fuse or breaker the cooker circuit should be connected to? This is often specified (not always), and if it is, this must be complied with, and may therefore influence the cable size you must use.

 

[Fleetwood]

CU in small porch in corner of open plan lounge so I assume cable run up into small bedroom above, then along landing under flooring - the length of which is the length of the stairwell - then a straight run into rear bedroom which is above small kitchen for about 6ft and down behind plaster to control unit, I assume its run that way, but who knows.

 

[kingeri]

That's the problem. On paper you may think that 4mm would do the job, but nobody on here can tell you how that cable is run, and what derating factors need to be applied to it. It really should be 6mm in my view. At least that's what I would install if starting from scratch. However, if having done all the calcs, and you work out that 4mm is ok, then that's your call. Just make sure you don't end up with the cooker and a separate socket outlet on a 4mm circuit.

 

[Fleetwood]

Kingeri there is no separate socket only the lower socket fed by the control unit. The spaec on the new oven is 32A protection. The connection cable they specify is oddly : 5 X 1.5mm or 3 X 2.5 mm or equivalent. This adds up to 7.5mm and there's no 7.5mm cable. 10 mm seems excessive, the next one down is 6mm which is below their spec.

 

[kingeri]

Hmm true that is odd. 10mm is excessive. You do need to connect in accordance with manufacturers instructions though. Guys........help us out here!

 

[Fleetwood]

Kingeri re your other post I'm not happy with it if it is 4mm at all, especially with the 32A MCB. Personally I think its 6mmm but squashed up in the socket box I'm not sure. Dont want ot cut off a sample as peeps these days dont seem to leave too much spare in boxes at best of times.

 

[trev]

"This adds up to 7.5mm and there's no 7.5mm cable. 10 mm seems excessive, the next one down is 6mm which is below their spec"
Manufacturer's spec gives minimum. Minimum does not exist. Nearest does not comply so you go bigger, simple really mate. It matter's not whether "It seems excessive"

 

[kingeri]

Fleetwood, Trev has said it really. More diplomatically than I could have. 10mm seems excessive to me too but if that's what's needed, then so be it. Remember, you can calculate the cable specs, diversity etc. all day long, but with a fixed appliance, the manufacturers instructions MUST be adhered to, and they override even BS7671.

 

[trev]

I don't understand what all the dithering is about mate. One doesn't exist, one doesn't comply so the answer must be.......?
I know it's important to get it right but come on, we're not performing surgery here