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Induction Hob again

Former Community Member
Former Community Member
I hope that you don’t find me impudent but I am having difficulty finding an electrician to explain why they will not install the induction hob and double oven that we are looking to fit in our new kitchen.
We have chosen a hob 7.4 kW and oven 6.3 kW. The cooker radial circuit has 6mm2 cable with 40A MCB. The run is some 12 m. The house was built (converted) in 2002 and inspected last year (DPN18C). We cannot run an extra cable because the CU is separated from the kitchen without a horizontal floor or roof space and presumably runs the existing cable through the stud walls.
The kitchen fitting company electrician has visited but won’t carry out the work unless we sign an indemnity as it would invalidate our insurance and the appliance guarantee. He suggested instead two plug-in ovens which we could add to the ring main. I have contacted four other local electricians but they all use 13.7 kW means 59.7 A which means 10 mm cable and ignore my request to consider diversity.
Should I give up and accept the two oven solution or perhaps a gas oven?
Do you know of a way of finding someone who understands diversity?
Am I simply wrong?

Parents
  • 0
    Hi Louie

    I'm afraid you have come across the problem we have with many electricians, they are keen to give opinions but only to their advantage! The problem we have is that the training is pretty poor and the exams that need to be passed are pretty trivial really and need very little understanding of the science behind the electrical system as a whole. This is illustrated by the EICR, electrical installation condition report, which is needed now for privately rented properties. Many of those produced (and I have a big pile of them here) are rubbish, the person issuing them has little understanding of the wiring regulations (BS7671) and in many cases report non-problems to get installation or repair work. There are a large number of electricians who think that a cable running at a few percent above the regulation rating will instantly catch fire, and have no understanding of the physics behind the magic number tabulated by BS7671. Whilst deliberate undersizing of conductors is unwise, the way that this should be approached is by means of the load profile, and the outcome of reasonableness is known as diversity. Deciding on this is very much an engineering judgement, although various suggestions are made in the "On-site Guide" and various other places. It is important to understand the features of the load, and its usage, as I have attempted to describe to you above. The whole subject is likely to become a matter of public difficulty soon, as the electrical supply to houses depends on a high degree of diversity, the supply available if all houses are using power is only 7-8 amps maximum, and electric car charging uses considerably more than this. The result will be a lot of blown substation fuses, power cuts and cable damage under the streets unless a great deal of new supply work is carried out. It has been estimated that £3 trillion will have to be spent if we shift to entirely electric vehicles, and there end up a similar number to cars etc. now. The Government do not seem to understand the problem, therefore is at least as bad as the electricians! I'm afraid they think that electricity grows on Green trees.


    David CEng etc.
Reply
  • 0
    Hi Louie

    I'm afraid you have come across the problem we have with many electricians, they are keen to give opinions but only to their advantage! The problem we have is that the training is pretty poor and the exams that need to be passed are pretty trivial really and need very little understanding of the science behind the electrical system as a whole. This is illustrated by the EICR, electrical installation condition report, which is needed now for privately rented properties. Many of those produced (and I have a big pile of them here) are rubbish, the person issuing them has little understanding of the wiring regulations (BS7671) and in many cases report non-problems to get installation or repair work. There are a large number of electricians who think that a cable running at a few percent above the regulation rating will instantly catch fire, and have no understanding of the physics behind the magic number tabulated by BS7671. Whilst deliberate undersizing of conductors is unwise, the way that this should be approached is by means of the load profile, and the outcome of reasonableness is known as diversity. Deciding on this is very much an engineering judgement, although various suggestions are made in the "On-site Guide" and various other places. It is important to understand the features of the load, and its usage, as I have attempted to describe to you above. The whole subject is likely to become a matter of public difficulty soon, as the electrical supply to houses depends on a high degree of diversity, the supply available if all houses are using power is only 7-8 amps maximum, and electric car charging uses considerably more than this. The result will be a lot of blown substation fuses, power cuts and cable damage under the streets unless a great deal of new supply work is carried out. It has been estimated that £3 trillion will have to be spent if we shift to entirely electric vehicles, and there end up a similar number to cars etc. now. The Government do not seem to understand the problem, therefore is at least as bad as the electricians! I'm afraid they think that electricity grows on Green trees.


    David CEng etc.
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