Induction Hob - Safe to use existing cooker circuit

[hallra]

Hello Forum,

I need to replace the hob in the kitchen as it is faulty.

I would like to be able to use an induction hob, so I need to make sure that the wiring and mcb on the cooker circuit is the right specification.

The combination Oven (1 small / 1 Large ) has a Max load of 4.1Kw.

The induction Hob has a Max load of 7.35Kw.

So that is a total of 11.45Kw.

The cooker circuit is on a 32a mcb.

The wiring is all 6mm T&E, a single cable goes from consumer unit to isolation switch, then splits into two 6mm cable, one to the oven, one to the hob.

It is a new build with all wiring hidden behind plasterboard walls and plasterboard ceiling.

From what I read, it appears that the 32a mcb and the 6mm cable is of adequate specification.

Obviously I want to make sure all is safe, so could you confirm this or advise what needs to be upgraded?


Thanks in advance


Richard

 

[Wilko]

Hi Richard and Welcome.
The 6mm and 32A mcb are the normal for domestic cooker circuits. Design wise they are likely to be ok for what you are proposing, based on the fact that not everything is on and demanding full power at the same time. That said, if I was installing for you I’d be closely reading the manufacturer’s installation instructions and inspecting and testing the existing circuit.

 

[hallra]

Hello Wilko and thank you for replying to my post.

As you have confirmed, which was my understanding, is that the cooker circuit is a standard U.K. design/specification.

With it being the standard design specification, I would hope that it is perfectly safe to use and the worse that can happen is if too much demand is place on the circuit is that the consumer unit would trip?

Thanks again in advance.

Richard

 

[cliffed]

It’s down to the load,with diversity should be ok.
If you were originally installing 1st fix you might be inclined to put a 10 mm in,but 32 amp,it’s ok..like wilko says.

 

[hallra]

Thank you both for your replies.

I agree, if it was a new brand new install then, 10mm would be preferable.

With it being a new build, with the methods of construction and the location of the Hob to the consumer unit, I don’t see an easy way to feed a new cable without a huge cost.

So the best thing I see, is to use the current cooker circuit and only install a new circuit if the current proves to be problematic when in use.
- Hence the only thing I wanted to check was that the safety components would protect in the event of an overload.
- I understand that overload protection has been part of Building Regs since mid 2000s...

The worse that can happen is a trip at an inconvenient time, which with only me and the misses is very unlikely, we don’t tend to have banquets

Thanks again

Richard

 

[telectrix]

can't see any problems with your current set-up. 6.0mm cable on a 32A MCB has always been good for cooking apploiances to a total rated load of 15kW.

 

[shaun1]

Overload protection has been part of the wiring regs since lomg before the 2000s. You are correct that the MCB should trip on overload, but you also need to make sure the connections are done properly in a suitably rated outlet plate. As these can overheat if done badly, particulalry with the higher current.

 

[GeorgeCooke]

I agree, if it was a new brand new install then, 10mm would be preferable.

No that would be a waste of copper and waste of money. Even 6mm is over the top. It is a 32 amp circuit and all that is required is 4mm cable. The purpose of the MCB is to protect the cable not the appliance on the end of it.

 

[Deleted account]

No that would be a waste of copper and waste of money. Even 6mm is over the top. It is a 32 amp circuit and all that is required is 4mm cable. The purpose of the MCB is to protect the cable not the appliance on the end of it.

Agree totally.
Too many installers go over the top with cooker circuits.

If you go to the time to work out actual cable calcs 4mm would normally be enough. Sometimes 6mm. I’ve never needed 10 mm, but seen it done too many times.

Hi hallra, your set up is absolutely fine.

 

[telectrix]

you total load is 49.78 A. round it to 50A,
the rules for diversity on a cooking appliances are:

10A + (30% of remainder) 12A = 22A ( add 5A if a socket is incorporated ).
so 6.0mm on a 32A MCB is perfect.

 

[Midwest]

I always apply diversity to the separate appliances, in this case hob & oven. Which still would be fine I would suggest.

 

[Taylortwocities]

You’ll probably need a dual connection unit to wire the hob and the oven.

 

[GeorgeCooke]

you total load is 49.78 A. round it to 50A,
the rules for diversity on a cooking appliances are:

10A + (30% of remainder) 12A = 22A ( add 5A if a socket is incorporated ).
so 6.0mm on a 32A MCB is perfect.

22+5 =27 which just happens to be the rating of 2.5mm cable.

However because it is on a 32a MCB we need to use 4mm, no more.

 

[davesparks]

22+5 =27 which just happens to be the rating of 2.5mm cable.

However because it is on a 32a MCB we need to use 4mm, no more.

without knowing the route and which rating factors apply how can you be so certain of the cable size? bearing in mind its a new build there will be plenty of insulation around the place.

 

[Deleted account]

I always apply diversity to the separate appliances, in this case hob & oven. Which still would be fine I would suggest.

Agree

As there are 2 appliances I would say

First 20A then 30% of remainder(9amps) total 29A

Plus 5A for socket 34Amps

The 6 mm cable in place is fine. The Mcb’s would then be 40A

I would also say the 32A Mcb’s would be fine as a bit of common sense adjustment calculations on diversity from the designer.

 

[BeardyJaws]

Agree totally.
Too many installers go over the top with cooker circuits.

I suspect that’s because we are told at college, or certainly at mine, that diversity applies to the DB and overall installation for working out capacity.
If the cooker is capable of drawing 50amps then we were told to design for that and not to apply diversity. But when you’re working out the total capacity of the DB diversity then applies.
I had the discussion at college and at work. If I apply diversity at college I would have failed that section. If I do as college says it goes against current practice from years of combined experienced professionals.
Anyone got a table I bang my head on? Manufacturers instructions to the rescue