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Manufacterer's advice/instructions

Been asked to connect up a used rangemaster all-electric cooker. No rating plate but model name is 'classic 90'. It has an induction hob.

Existing cable is 6.00mm on a 32A mcb.

Phoned the manufacturer who said it would be fine, since diversity could be applied but we would have to fit a cooker switch without a built in 13a socket and uprate the mcb to 40A.

I am a little troubled to say the least.

Comments welcome.
  • Former Community Member
    0 Former Community Member
    Is that the long and short of it Chris?


    How long is the turkey in the oven for?!!!!!


    Regards


    BOD


    PS check your PM.........!

  • John Peckham:

    You cannot apply diversity to a single piece of equipment for sizing circuit protection and cable sizing. Diversity can be applied to individual items of equipment when considering the maximum load on a distribution circuit or an installation.


    The cable and the circuit protection should be rated for the "Plated" load or the manufacturers instructions.




    Fair point!


    If you were silly enough to turn on every single part of the cooker in one go, it would indeed draw gazillions of amps.


    Problem in the OP is that there is no plate.


    I fear that the problem is that one-upmanship encourages the manufacturers to declare the maximum possible power. However, it is perfectly reasonable for them to specify a smaller cable in the small print than may otherwise be expected.


  • perspicacious:

    How does 433.1 fare?




    I thought that we were considering a big overload of short duration. ?

    311.1

  • Former Community Member
    0 Former Community Member
    Remember that a cable (and a fuse or thermal element of an MCB) will take time to heat up - shove 50A or 60A down a 6mm² cable starting from cold and it'll take several tens of minutes to warm up to 70 degrees - by which time the oven thermostat will have started switching the oven off every few minutes and the pans will have started to boil and been turned down to a simmer setting. The '10A and 30%' rule has been used successfully for probably hundreds of millions of Christmas dinners by now (plus countless everyday meals) and seems to have been perfectly satisfactory.


    How does 433.1 fare?


    Regards


    BOD

  • John Peckham:

    `You cannot apply diversity to a single piece of equipment for sizing circuit protection and cable sizing. Diversity can be applied to individual items of equipment when considering the maximum load on a distribution circuit or an installation.


    The cable and the circuit protection should be rated for the "Plated" load or the manufacturers instructions.




    In general I agree, but not in the case of cookers. A cooker typically consists of one or two ovens, several rings and perhaps a grill. The chance of all these components being fully utilised at the same time and for more than a couple of minutes is very small and an apparently undersized cable and MCB will almost always serve well.

    If a single very large oven has a loading of 15KW then it needs a cable and MCB sized for 15Kw. If a cooker has a combined loading of 15Kw then it can use a smaller circuit.

  • `You cannot apply diversity to a single piece of equipment for sizing circuit protection and cable sizing. Diversity can be applied to individual items of equipment when considering the maximum load on a distribution circuit or an installation.


    The cable and the circuit protection should be rated for the "Plated" load or the manufacturers instructions.
  • Gentlemen, I thank you for your replies. I shall advise that we leave it as be, but if they experience problems, then we may have to uprate.
  • 6 mm2 T&E is good for 47 A in ordinary walls (Table 4A2 no. 57 or 58; Table 4D5, RM C).


    A 40 A MCB will be thinking of tripping within an hour or so at 58 A (Figure 3A4).


    However, as others have pointed out, diversity allows plenty of headroom. After all, you don't put your peas on to boil at the same time as meat goes in the oven.
  • Unless there are going to be more people eating than previously, the amount of food to be cooked will not change much, and therefore the heat demand, if anything a newer cooker may be better insulated oven etc.

    I'd be inclined to connect to the current circuit, and so long as the breaker protects the cable, just  let them know that if they work it unusually hard, the circuit that supplies it may trip, and if that happens more than occasionally,  then the wiring will need to be upgraded to a heavier cable and breaker. Equally, what is the building incomer - if it is 60 or 80, then 40 is a large chunk of it.)

  • I began to wonder if the old method still applied in the same way to ceramic and inductive heating methods as it did to purely resistive ones and that I was missing something.



    My head thinks that even if the new technologies draw current in somewhat different ways to simple resistive heating (e.g. more pulses of larger current but only for part of the time) the overall heating effect on cables (and overload protective devices) will be averaged out over reasonably long lengths of time (tens of minutes) - so we only need to worry about the average current overall rather than individual peaks. The average current will be directly related to the heat the load produces - so a 1kW resistive hob will average the same as a 1kW induction hob. If anything induction tends to be a little more efficient (by heating the pan directly) so the users will likely have it turned down a notch or two compared with what they would have done with a traditional hob of the same rating (or will have it on for a shorter time) - so we should if anything be even safer using the old methods for new appliances.


    If it's of any reassurance, I've got a 7 point something kW induction hob at home that's survived perfectly well on a B20 RCBO - including several Christmas meals for the extended family.


       - Andy.