Induction Cooker Cable

[neuron]

I'm thinking of buying a freestanding electric induction cooker. There's a limited choice out there but it seems the ones I've found have typical power consumption of 17.1kw, 13.6kw, 12.0kw, 10.67kw or 9.8kw.

I have a cooker circuit which uses 6mm squared TW/E along its entire length of around 6 metres. Most of the cable is not enclosed in trunking or walls and is freely exposed to air. The cooker MCB in the consumer unit is rated at 32A and the cooker control unit has a socket on it.

I've been reading about the electrical requirements for this type of circuit and I understand that when the 30% diversity factor is taken into account, the circuit is adequate to supply power to any of the above cookers ie the present mcb and cable fit the bill. I've worked it out on paper myself and the amperage easily falls within the 41/47 amp limit for this size cable.

Furthermore, the manuals for the cookers all state that a 32A amp mcb is what is required along with a 6mm squared cable to power the cookers! It's all something to do with the cookers being built for the UK market along with the cable size and mcb being regarded as standard.

Could I have some comments on this please?

[The Builder]

A veritable can of worms here Neuron. You'll get many different takes on this, depending on who you ask.

Yes, applying Diversity will certainly allow the use of 6mm cable plus 32A MCB.
This does assume that the cable really is routed so that no de-rating is necessary.

I think I can safely say that most Electricians would upgrade the cable to a 10mm for the 13.6kw and the 17.1kw, considering that the 17.1 has a potential draw of 71A.

The 32A breaker is the key here. With that, the cable is protected. What Electricians try to avoid is the possibility that at Christmas for instance, the whole lot could be on. Manufacturers know that all elements constantly switch on and off during use (thermostatic). Overload is thus less likely, but no one wants to be called out because the 32A breaker keeps operating due to overcurrent.

I would say that, theoretically, you're OK.......... but ............ I would be much happier if BRIGHT SPARK of this Parish sees this and gives his opinion. Hopefully he'll see this.

[BRIGHT SPARK]

TB is correct... as per.However the 17.1kW can operate with the 6mm2 (providing that no corrections are needed), but the 32a mcb will be overloaded...37.29A.
This will give you a headache if you load the appliance fully.If you go with the 17.1kW a 10mm2 cable with a 40A mcb would be a better choice.

[The Builder]

Now I'm happier :o)

Thanks BS

[Referee-Observer]

Regarding the cross sectional area of the supply cable, consideration must also be taken into account of the volt drop. A 10mm squared cable and 40A MCB would be my choice for loading and volt drop for the higher rated cookers. Volt drop is dependent on loading and length of cable.

[BRIGHT SPARK]

Ref....The volt drop comes in at 10.29V...just below the 5% limit.

[Referee-Observer]

Phew, close..!!

[neuron]

Thank you all for your help.

SB, if decided to buy the 12.0Kw cooker would this be OK on the existing cable and MCB?

I've worked out using the wiring regulations that the 12.0Kw cooker would use 27.65A inclusive of the 5A allowance for the socket on the cooker control unit which would seem to point to the 32A MCB being adequate. Given that the 6mm2 cable in my circumstances could carry 47A, it seems ok on paper.

If it is OK, would there be any advantage to changing the MCB to a 40A rating given that the MCB is there to protect the cable rather than the cooker?

Alternatively, am I missing something here?

Thank you

[BRIGHT SPARK]

Yes the 12kW will be ok for cable and mcb.The 40A mcb will in theory protect the cable as the rating is 46A ...HOWEVER this could lead to overheating if the appliance is fully loaded..i.e. up to 74A...... because the mcb will carry a steady 60A all day long.
(The correct calc for a 17kW is 34.17A not 37.29A)

[neuron]

Thanks BRIGHT SPARK, that's clarified the matter for me.

I'm very grateful.