Hard Wireing a 10kw Electric Cooker.

[lukeinea]

On 25/02/08 nattye84 asked a question about this
subject which was very well answered and understood
Following on from this I need to install a 10mtr cable
between the consumer box and the Isolation Switch
near the cooker. (8mtrs in the roof void and just 1.5 mtrs
in plastic conduit inset into a breeze and plastered wall.
Like nattye84 my cooker just says 10kw output wired to
a 45amp fuse. What would be the best cable to use
6mm with a 32amp mcb or 10mm with a 40amp mcb.
I was intending to err on the side of caution and use
10mm cable and 40amp mcb. Can anyone advise me
please. Thankyou.

[zingo1327]

hi
Not the answer you want but get a qualified electrician. What you are doing is dangerous and because it wouldn't have been done by a qualified person your home insurance would not cover you in the case of electrocution or fire

[lukeinea]

Your right zingo not the answer I wanted. I have an electrician who will make the actual connections.
I just intend chasing in the cable and wanted a third opinion as to the correct size cable to use taking into
account that the cooker says a 45 amp MCB and I can
only find a 40amp to fit my consumer unit. My current cooker is on a 32amp with 6mm cable and as stated
on the response to nattye's question on 25/02/98 if diversity is applied this should be adequate but what
about the 45amp mcb recommended by the manfacture
who also state it is a 10kw cooker. Something wrong somewhere.

[lukeinea]

To simplify things the purpose of my question is to get
other opinions of the most appropriate size cable to use
bearing in mind that I can only get a 40 amp mcb for my
consumer unit Thank you..

[Broadie451]

I have a few questions for you,

what is the total length of run of the cable?

how thick is the insulation if the roof void, how are you going to support the cable in the roof void?

what type of mcb do you have in your consumer unit, ie type 1,2,3 or b,c?

Is it a freestanding cooker or seperate hob and oven?

[lukeinea]

Hi Broadie,
Building is a bungalow brick and tile.
Length of run would be 10 metres maximum from
consumer unit to cooker connection box.
4 metres in loft space with 4" fibre glass insulation.
3 metres through void of flat roof extension with same
4" insulation.
1 metre chased into block wall in plastic condiut to isolation switch with 13 amp socket.
1 metre chased in same wall to connection box.
Cable would be laid across ceiling joists and fixed with cable clips as necessary to keep it tidy. (unless you have a better suggestion).
Consumer unit is currently a Square D Quickline with a 6mm cooker wire on a B32 MCB,
I will probably have this changed at some point as I have
a Wylex split unit with both NSB32 and NSB 40 MCBs.
It is also intended to uprate the loft insulation before next
winter so best to work on the current standard.
Cooker is freestanding. 10kw output, ceramic rings and
large and small (Grill) ovens.

[Hymie]

10kW at 230V represents a current draw of just over 40A � therefore you need 10mm squared cable.

With a 40A MCB you might get nuisance tripping, but I doubt it � pedants would insist on a 50A MCB.

[terence7556]

luke the problem with your question is that on here you get various opinions , of which i will offer another, and this is not fair to you or your electrician friend who will ultimately take responsibility for the design, installation and any inspecting/testing
a cooker is an item that allows diversity to be taken into account,as you stated, in other words what percentage of the connected load is likely to be used at any one time.will you have every ring and the oven on at any one time? unlikely
so 10000/230 = 43.5 amps
first 10 amps plus 30% of the remainder plus 5amps if the cooker has a socket outlet
33/30% =9.9 amps
so 10amps +9.9amps+5amps = 24.5 amps
this is not definitive but can you now see why you need 6mm cable + a 32 amp mcb
say you fit 10mm cable. ok might cost you more than you need to spend ,so what.
but the larger mcb may not trip out when required under fault conditions and this is important
i would suggest you leave it to your sparky as there are many factors not even considered yet

[Disco Fever]

I'm a sparky and you will also have to take into account the loft insulation which could make the cable overheat if the load is at the limit so there is a correction factor in the IEE wiring regs.

Ive looked into the cable size in the 16th edition IEE regs book, I havent been on the course yet for the 17th which is out now but this will give you a rough guide, a 10mm twin & earth enclosed in an insulated wall is rated at 43 amps and the same cable enclose in conduit on a wall or ceiling or trunking is rated at 52 amps. So you can take it that you will have to go with the 43 amps so you can only use a 40 amp MCB unless you want to upgrade the cable to 16mm and then you will be covered if you have a 50 amp MCB installed.

[Broadie451]

Hi Lukeninea,
Hymie is quite correct in saying that a load of 10KW would draw in excess of 40A, but it's not as straight forward as that when we start talking about cookers because we can apply diversity to the cable calc, since the full load is not always used whilst the cooker is in operation.

From the information you have provided the length of run is 10m, the load is 10KW which would equate to an initial design current of 43.48A, but after diversity (100% for the first 10A plus 30% of the rest of the load plus an extra 5A for the control unit with a socket outlet gives a total load of 25.04A, using your 32A rated type B mcb the tabulated current carrying capacity of the cable taking into account the 100mm of insulation would be 39.51A, meaning a 6mm cable with a 2.5mm CPC (earth), would be sufficient. (using reference method 1 clipped direct 6mm max current load is 47A 10mm would be 65A).

If you are to increase the insulation in the roof space then I would strongly reccomend that you install the 10mm cable, because the tabulated current carrying capacity would have increased to over 47A with an increase of insulation depth.

As mentioned if you change from the original wiring specification you will need to have a qualified electrican to certify the work, he will have to fill out a minor works certificate for this job.

I hope this points you in the right direction,

[Broadie451]

Hi Lukeinea,

I have re read your answer regarding the insulation and if the cable is totally surrounded by insulation, (say for example you have holes cut through the joists in the flat roof extension and the is insulation inbetween the joists that the cable will go through) you are going to have to install a 10mm because of the derating factors of the insulation.

As terrence has already mentioned "i would suggest you leave it to your sparky as there are many factors not even considered yet"

[BillyNoMates]

And if your isolation switch by the cooker has a socket it must be RCD protected.

(assuming working to 16th Edition regs and cooker is on a ground floor)