Manufacterer's advice/instructions

I would be a bit doubtful about telephone advice that is not part of the written instructions.

I would be inclined to use cable and MCB size as recommended in the written instructions, if these are not to hand, they should be obtainable on line.

A smaller cable than recommended  if correctly protected by an MCB should not be dangerous but does of course carry the risk of nuisance tripping under heavy use of the cooker.

I agree - hence my doubts.

The unit is 2nd hand and no paperwork came with it apparently. Not sure now if the hob bit is ceramic or induction. The model does not seem to come up on Rangemaster's website.so it must have been superceeded.

All I do know for sure is that it is a 900mm model and is all-electric.

What's the worry? -  a classic 32A circuit should be good for a domestic cooker up to around 19kW f.l. rating (presuming no socket on the CCU).


Is this the one http://www.rangemaster.co.uk/products/range-cookers/classic/classic-90-induction? (or similar enough)


The spec says 7.4kW total for the hob, 2.3kW for the grill, I can't see a rating for the oven, but let's say they're not more than 3kW each (for two of them) - so that's still only 15.7kW.


   - Andy.

Andy,

Just been looking again. The model looks to be a different one to that.The closest rating I came up with was 14.74KW.

Splitting hairs I know, but 6.0mm? Even with a 40A it's running close.to 65A?

The closest rating I came up with was 14.74KW.

Splitting hairs I know, but 6.0mm? Even with a 40A it's running close.to 65A?

But there's a large amount of diversity for domestic cooking appliances. The usual rule (which goes back a couple of generations at least) is 100% of the first 10A and 30% of the remainder (plus 5A if the cooker circuit also supplies a socket). So your 65A (full load) only really needs a 26.5A circuit.


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.


  - Andy.

I get it, but I am a compulsive worrier! The cagey remarks from the manufacturer about not using a cooker switch with an integral socket outlet (which the present one has) had me doubting. 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. A rating is a rating, but the nature of the loads are different?

I'll most likely stick a 40A mcb in to cover it and see how it behaves.

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.

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.)

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.

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.