Induction hob - dedicated feed

[doog442]

Hi. We've had various quotes for a new kitchen.

We're looking at replacing a gas hob with an induction hob rated 32amp / 7400 w. Below the hob will be two electric ovens side by side (13amp) 2770w as we have now.

Two fitters have said the hob can connect to the current dedicated cooker feed and two other quotes have said the hob will need its own dedicated feed from the fuse box.

Running this new feed from the fuse box is going to cause complications due to the location of the fuse box, possibly lifting new flooring upstairs or removing coving, reskimming ceilings as an alternative route. Needless to say its an additional expense.

I wonder if the experts on here can supply a clear answer. I suspect it will need a separate feed. The house (5 bed - 3 electric showers) actually has two separate fuse boxes - one feeding a substantial extension added including one of the showers.

Cheers.

 

[EFLImpudence]

We're looking at replacing a gas hob with an induction hob rated 32amp / 7400 w. Below the hob will be two electric ovens side by side (13amp) 2770w as we have now.

Ok, so a total of 12,940W - equivalent to a stand alone cooker.

This works out to 54A, but for cooking appliances, because they cycle on and off even when on, we use a diversity calculation of
the first 10 Amps plus 30% of the remainder.

So 44 x 0.3 = 13.2 + 10 = 23.2 (plus 5 if there is a socket on the cooker switch)

Therefore your 32A standard cooker circuit (if that is what it is) will be fine.

Two fitters have said the hob can connect to the current dedicated cooker feed

Presumably you mean as well as the two ovens, in which case they are correct.

and two other quotes have said the hob will need its own dedicated feed from the fuse box.

Tell them to go away and figure out what they would do if it were a single cooker of 13kW.

 

[doog442]

Many thanks, yes 32 Amp standard cooker circuit. That will save a load of work and hassle.

 

[ericmark]

My stand alone cooker has two ovens and induction hob, now must be well over 10 years old and has never tripped the 32 amp overload, and that is the worse case scenario, not really a problem since we stopped using fuses, you just let it cool then reset.

The induction hob wastes less power than the old hobs, so clearly uses less power, the old ceramic hob never tripped the 32 amp MCB so the new induction uses less, so not much chance it will ever trip.

 

[plugwash]

There is a concept in electrical installation design called "diversity", the basic idea is that it would be ludicrous to assume that all appliances would be operating at full power all of the time. So we don't, we design based on some anticipation of likely load.

There are diversity guidelines, but they are not hard and fast rules. The guidelines for cooking equipment in domestic installations are relatively unusual in that they only look at the total load, most guidelines for other situations look at the ratings of individual appliances as well. The guidelines have not changed significantly in a very long time.

Anyway the guidelines for domestic cooker circuits are.

First 10A, plus 30% of the remainder plus 5A if there is a socket.

If we take the wattage figures then you have 32A for the hob, plus 2*12A for the oven, that's 56A total running that through the diversity guideline we get.

10 + (56-10) *0.3 = 23.8, so even with all your cooking equipment and a socket on the cooker circuit you are well within the guidelines.

Nevertheless some electricans rightly or wrongly get nervous about putting close to double the circuit's rating worth of load on a circuit. Especially when there is "new" technology that they don't understand involved.

 

[ebee]

Hello. There is a diversity calculation that has pretty much stood the test of time therefore we usually use it. note - it is only a rule of thumb though so. in some circumstances, it might need a tweek. example, more use than normal for instance use by 3 or 4 families rather than the usual one family or say use frequently by a business such as a cafe. however i think for your situation that rule of thumb might well suffice. i would be more concerned by the fact you have three electric showers, that is a potential to draw a lot of power at any one time. if this is avoided by a strict usage regime or by using shower priority devices then fair enough but (another rule of thumb) one single phase supply then one electric shower max is often the case.

some more food for thought, overloading of socket circuits example. lets say there are two identical houses, each with 2 adults and 2.4 children. house A has 12 twin sockets yet house B has 75 twin sockets. house B potentially could draw more load but in practice would it? the answer is probably not