Cable size and live wire colour change

F

Fleetwood

Hi Can anyone remember which came first, the change of cable size to metric from imperial or the change to brown for live conductor? I've come across a cooker supply cable with new colour code of Brown,Blue + Earth but it is 7 stranded. Difficult to tell it it is 7/029 or 7/036. Could be the later as it seems a little light for 7/044. It feeds via a 32a MCB. Anyone recall using stranded new colour twin and earth?
 
New (and old) colour 4mm upwards is stranded! Imperial cables went out way before harmonised colours came in!
 
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Thanks Kingeri. Bit concerned it could be 4mm as it's terminated in a 13a socket as the cooker outlet box. It's in a rented house that my daughter's new boy friend is taking on and they need to know what wattage combined oven/hob they can buy. They have their eye on a 10.5Kw Beco and with diversity I've worked out that it should be ok with a 6mm cable fed from a 32A MCB. Having said that, this Beco has an unusual suggested cable spec. ie 5 X 1.5mm, 3 X 2.5mm or equivalent. That is suggesting a 7.5 mm cable (which there isn't). 10mm seems an overkill for situation seeing as how with diversity we about 21A flowing. Any comments would be appreciated.
 
Am I correct in thinking that the 10.5Kw oven/hob is still ok even if the cable turns out to be 4mm? This oven needs to be hard wired so the 13a socket needs to be changed to a normal control box?
 
No offence, but I can tell the difference between 4mm and 6mm at a glance! 10.5kw with diversity would need 6mm. And yes, you need a cooker isolator, certainly not a socket outlet!
 
Sorry Kingeri, I'm misleading you drastically - had a long day. There is a cooker control unit with combined socket but what I meant was that there was a 13a socket as a connection box. This the one the cooker is connected to.
 
and are you concerned with the main cable to the cooker switch, the cable from the cooker switch to the socket, or both
 
Sorry, I'm confused. At the end of the day you want to end up with a 6mm feed to either a cooker control or a cooker control with integrated socket, and that's it. Nothing else. You don't want any additional cable going to a socket. It should be a radial circuit that terminates at the cooker switch. Or am I misunderstanding?
 
Kingeri I will recap. The circuit is fed from a 32A MCB with 6mm(?) cable to a cooker control with integrated socket and then down to a further switched socket. This is what I think should be a normal connection box. (The type that can take up to 2 10mm cables ) Don't know why its a socket unless the previous oven was without an electric hob. This is possible as there is a gas connection point in close proximity so there may have been a gas hob. Therefore then that oven may have used a 13A plug.
This new Beco, being 10.5 KW has to be hard wired so I need a proper connection box. Would have thought that the cable is 6mm as the MCB is rated 32A. THis is too high for 4mm cable. Just wanted to be sure cable is 6mm because new oven is 10.5KW. If the cable for some reason is 4mm, this would have been ok with a low wattage oven on a plug - even if the MCB was wrongly rated at 32A - but certainly not ok for 10.5 oven/hob.
 
[FONT=&amp]Imperial T+E Cable sizes were phased out in the late 1960s but still available up until the introduction of 14th Edition:1966+A3:1970
Harmonised Colours implemented from March 2004 onward with the introduction of BS7671:2001+A2:2004[/FONT]
 
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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).
 
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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?
 
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.
 
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.
 
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.
 
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.
 
Hmm true that is odd. 10mm is excessive. You do need to connect in accordance with manufacturers instructions though. Guys........help us out here!
 
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.
 
"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"
 
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.
 
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
 
Why not for a moment put the manufacturers spec aside other than they spec a 32 amp mcb

Depending on the installation method.the 4mm may be adequate,albeit at a push and not the more usual 6.0mm or 10.0mm
So in that respect the 4.0mm could be used

The manufacturer is specifying the cable size without all the other factors that help make that decision,how they have got this information would be interesting to know
I can understand specifying minimum 6.0mm or 10.0mm to try and leave room for lower current carrying capacity of a cable

It seems odd that a manufacturer is specifying a minimum cable size that is non standard
It seems as if they have taken the worst scenario installation method for the cable that will carry the diversified load of their appliance,then plucked a cable size out of the air
In the end, the cable capacity, installation method and the mcb rating is what will govern the need,but this manufacturers priority in the wiring regs should be considered by the IET in this day and age
 
Yes guys but the cable from the CU is not 10mm, I would say 6mm. So on the basis of the spec where does that put us. What about diversity.
 
Just in case, I'll take some 6mm to compare.Have doubts from a quick look in isolation.Normally is it not more usual to install 6mm than 4mm for cooker feeds. It was the 13A socket as the connection socket that caused my doubts. maybe it was oringinally installed for oven without hob and thus lower wattage. Why use a 13A socket - to make it easy for the then householder to plufg the oven in. Was it therefore wired to suit that householder without considering that someone may follow with a bigger oven. I cant find the spec for the oven at the moment but the ceramic hob had 2X 1700W : 2 X 1200W a 2K grill (I think) and a fan oven (dont know wattage of that one). Surely doesnt justify 10mm cable.
 
I'd ( recklessly ) ignore the oven manufacturers suggested cable size as they are clealy using a standard not used in the UK.
If you know the load of the appliance , whether in kw or amps , then a competant installer should be able to calculate the correct fuse / cable size.
And if the circuit is to be connected to a 32A mcb and isnt going to be covered with 2 ft of insulation , then i cant think of a single reason why you would need to use 10mm when 6mm will suffice.
 
The connection cable they specify is oddly : 5 X 1.5mm or 3 X 2.5 mm or equivalent.

This would seem to be 3 phase/ single phase cooker and the cable rating you are stating are those values for the cooker tail ?​
 
Hi Fleetwood,

I have fitted a similar cooker oven to this before, ie. 3X 2.5 mm cable.

I seem to remember that you will struggle to fit 10mm cable, also if I recall the hob was split in two, ie. one 2.5mm to two plates, another 2.5mm to the other two (of four in total) and a 2.5mm to the grill and/or oven, bloody awkward, but doable.

Seeing as how the whole shooting match is wired in 6mm from the DB, you could do as I did and that is fit your 6mm to the centre blocks, and use 6mm or 2.5mm 'jumper links' to the the other two connection blocks, there are three connection points or terminal blocks on the one I did, there is no way you would be able to use 10mm cable to interconnect these.

Or you could just do as the manufacturer recommends and use 3X 2.5mm.

Ps. you will need to change that socket outlet to a cooker connection point.
 
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As for diversity , well lets go through it together.....

10.5kw / 230v = 45A

diversity of cooker = First 10A + 30% of remainder + 5A for skt

10A + 11.6 A + 5 = 27A

Therefore 32A mcb on 6mm will be fine.
Also 32A mcb on 4mm will also be fine , installation methods and circuit length permitting.
 
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Cable size and live wire colour change
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