How do you wire a 7,5kW electric cooker?

[mikex79]

hello my colleagues electricians
I need to wire 7,5 kW cooker, the cable run will be 15 meters clipped direct what would be the MCB and cable size. from my calculation I work out it should be 40A B MCB and 6mm2 twin&earth but can anyone tell me if I can use 4mm2 instead and/or 32A B MCB.

Ib=P/V=7500/230=32,6 but who has ever used the full power of an appliance?

I also checked the voltage drop and Zs for both cable sizes and MCBs just need to make sure that 40A and 6mm2 T&E won’t be overestimated.
any advices?
regards
Michael

 

[Mac]

hello my colleagues electricians
I need to wire 7,5 kW cooker, the cable run will be 15 meters clipped direct what would be the MCB and cable size. from my calculation I work out it should be 40A B MCB and 6mm2 twin&earth but can anyone tell me if I can use 4mm2 instead and/or 32A B MCB.

Ib=P/V=7500/230=32,6 but who has ever used the full power of an appliance?

I also checked the voltage drop and Zs for both cable sizes and MCBs just need to make sure that 40A and 6mm2 T&E won’t be overestimated.
any advices?
regards
Michael

Cable Size Selector Calculator and online cable selector for electricians

Take a look at this mate.Works it all out for you.It is only a guidance thou

 

[mikex79]

Cable Size Selector Calculator and online cable selector for electricians

Take a look at this mate.Works it all out for you.It is only a guidance thou

alright the website calculater says that 4mm2 will be alright but in this case i need to use a 32A mcb to protect the circuit but what i am worried about is that it will trip as the Ib is a bit over 32A

 

[Mac]

This is how i worked it out by applying diversity

I=P/U=7500/230=32.6A-10A(15A)if the cooker point has a socket=22.6A - 30%.
15.82X30/100=4.746+10=14.746A(19.476A) if the cooker point has a socket.That is under the assumption that the oven and all the rings are not on at the same time.32 A MCB fine mate

 

[mikex79]

This is how i worked it out by applying diversity

I=P/U=7500/230=32.6A-10A(15A)if the cooker point has a socket=22.6A - 30%.
15.82X30/100=4.746+10=14.746A(19.476A) if the cooker point has a socket.That is under the assumption that the oven and all the rings are not on at the same time.32 A MCB fine mate

once again to make sure 32A mcb and 4mm2 wire for 15m cable run? am i right?
regards

 

[Mac]

once again to make sure 32A mcb and 4mm2 wire for 15m cable run? am i right?
regards

Yes mate you are right but i would still put a 6mm cable.If the CCU has a socket it would need to be RCD protected as well

 

[mikex79]

I have just spoken to the landlors and he says that in the flat where the cooker gonna be will live 6 or 7 people for use of thet cooker and it makes me think to use 6mm2 cable and 40 A fuse as diversity may differ from what is in on site guide and the cooker may be on at all time with full power on. what do you think?

 

[lister]

From experiance mate definatly use 6mm, and i think you will be fine on 32a mcb, in practice diversity plays a big part so does voltage, in the real world you will find its nearer to 240V and some, thus lowering current.
Relax dont worry, stick it in

 

[Guest123]

6mm 32A MCB.

 

[Paul P]

6mm 32A MCB.

QFA Would never consider an all electric cooker on less than that.

 

[cheeky_blue]

I do a lot of cooker circuits through a contact of mine. Pretty much all are done using 6mm and a 32A breaker.

 

[Graeme Harrold]

I have just spoken to the landlors and he says that in the flat where the cooker gonna be will live 6 or 7 people for use of thet cooker and it makes me think to use 6mm2 cable and 40 A fuse as diversity may differ from what is in on site guide and the cooker may be on at all time with full power on. what do you think?

Who would want to apply full diversity to a cooker circuit knowing the time its guarenteed to be at full tilt is XMAS. Apply on the cert, but wire big.......

 

[NoSparks]

Mac,

Sorry you were a bit quick for me there. did you say:

10 + (32.6 - 10) *30% + 5
= 10 + 22.6 * 0.3 + 5
= 10 + 6.78 + 5
= 21.78

Thing is I thought these tables were for calculating the maximum demand for an installation taking into account that not all circuits will be at full load at the same time. (Thus the tails and supply cutout can be sized smaller than the sum of the circuits).

Another view is that a domestic cooker is most unlikely, even at christmas, to be used for more than 20 minutes (1200 sec) at full load. A 32A MCB will sustain a load of about 48amps for this period of time without cutting out.

So theoretically and assuming wireing method C, Michael could, as the calculator suggests, use 4mm on a B32 if there is no socket, or 6mm cable and a B32 if a socket is included.

Me, well I frequently over-enginear and also look to possible future enhancements, so I would go for a 6mm and a B40. Over 15m the cost difference is going to be negligible, so hay.......

Geoff

PS. It would of course have to be a B32 if there was any possibility of the cable passing through an insulated space. (Wireing method A) Hence aligning with what Cheaky Blue does as "norm".