4mm cable, 32a breaker for 16.2kw Rangemaster installed by electrician

[Chris C300]

Hi, during kitchen refurbishment, the electrician installed a 4mm cable and 32a breaker for the new induction hob rangemaster oven that is rated at 16.2kw.

Same electrician couldn't connect hook up cooker, so I asked someone else to do it. The new electrician refused to connect up saying it needs a 10mm cable 45a breaker. Both professionals are in disagreement. Would be great to get a consensus here please. I want to use the oven without concern it may trip the breaker (5 induction hobs, 2 ovens and warming drawer)

Thanks

 

[Pretty Mouth]

Hi, thanks everyone for your comments

Thanks all, here are the calcs from installer aimed to reassure me. Final thoughts on this would be really appreciated. At this point looks like I will be asking him to change to 10mm, may as well if changing from 4mm as you say. But there will no doubt be a difference of opinion. Thanks again

INSTALLER CALCS:
Your range is rated at 16kw, this equates to 69.57a (16000/230).

This figure isn't the end of the matter however.

BS7671 states we are to apply a principle called diversity. Your range oven even with everything on won't pull 69.57 amps as it's not a purely resistive load. -Elements actually switch on/off to keep temperature.
Diversity law states you calculate your actual cooker load as 10 amps plus 30% of the remainder. (In your case 10 amps plus 30% of 59.57 amps or 17.87 amps.

This equates to 27.87 amps.

Now we know the actual load we must design the circuit so the safety device (mcb) exceeds this, (yours is a 32a device); and the cable current carrying capacity exceeds the safety device. I chose 4mm cable which can carry 37a when it's clipped direct to wood, and not grouped with other circuits ie in your type of installation.

Basically the maths is to ensure the cooker can pull its load without the breaker going.
If something goes wrong, the breaker will go before the cable reaches its maximum load
In your case load 27.87a < 32a mcb < 37a cable.

Hi Chris,

Having read the email that you posted from rangemaster, your electrician's calculations, and had a quick look through the manual, I would say this is probably going to be okay.

The instructions don't insist on a 10mm/45A circuit, (although there is, I believe, a youtube video by rangemaster/aga that suggests it should be used). Rangemaster's email said it will be ok on a 32A circuit. Your electrician has provided a 32A circuit, and his calculations look okay to me.

 

[timhoward]

Now we know the 4mm is clipped direct I would also agree that it looks ok. Just because I wouldn't have installed it myself and it's not a common choice for cooking appliance circuits doesn't mean it is non-compliant.

 

[Chris C300]

Now we know the 4mm is clipped direct I would also agree that it looks ok. Just because I wouldn't have installed it myself and it's not a common choice for cooking appliance circuits doesn't mean it is non-compliant.

OK, thanks fornthe confirmation. Its good to know that although not a popular choice, should be able to run the range as intended. Thanks again everyone for your input

 

[nicebutdim]

OK, thanks fornthe confirmation. Its good to know that although not a popular choice, should be able to run the range as intended. Thanks again everyone for your input

One electrician has laid out the calculations involved, while the other has quoted what they consider to be best practice. While 4mm might not be a popular choice, that electrician has demonstrated a decent level of competence in arriving at their chosen cable size.

 

[Baddegg]

Personally I’d go with MI cos you can guarantee the one time it’s all on and trips will be Christmas Day and I don’t want you call me

 

[swaRRR]

I always find it odd when someone employs a fully qualified electrician and then questions everything they say.

 

[brianmoooore]

Ordinary T&E may be rated at 70 degrees, but that's hotter than the maximum allowed from a domestic hot water tap. If I installed a cable in a domestic property that ran at anywhere near that temperature, I'd expect the customer to be on the 'phone pronto.

 

[DPG]

I always find it odd when someone employs a fully qualified electrician and then questions everything they say.

He didn't. The electrician refused to connect it up.

 

[timhoward]

Personally I’d go with MI cos you can guarantee the one time it’s all on and trips will be Christmas Day and I don’t want you call me

I was also thinking about Christmas Day - there's a country estate I look after that only has a 3 phase 100A supply for multiple dwellings, and Christmas Day is the reason that I as an electrician have been insisting on changing a few cookers to gas!

I always find it odd when someone employs a fully qualified electrician and then questions everything they say.

Be fair. The questions only started when a 2nd fully qualified electrician disagreed, and then what chance does Joe Public have of working out who is right? (I'd privately decided it was unlikely to be ok until it was established it is clipped direct.)

 

[UNG]

Ordinary T&E may be rated at 70 degrees, but that's hotter than the maximum allowed from a domestic hot water tap. If I installed a cable in a domestic property that ran at anywhere near that temperature, I'd expect the customer to be on the 'phone pronto.

The cable running hot is one thing but how often are the terminations going to be checked for thermal creep and heat damage

 

[Pretty Mouth]

Ordinary T&E may be rated at 70 degrees, but that's hotter than the maximum allowed from a domestic hot water tap. If I installed a cable in a domestic property that ran at anywhere near that temperature, I'd expect the customer to be on the 'phone pronto.

I don't think it will get to that temperature in this case. Expected load is <28A, with the cable rated at 37A, it shouldn't get anywhere near that hot.

 

[Chris C300]

I always find it odd when someone employs a fully qualified electrician and then questions everything they say.

...Because a second qualified electrician would not fit the appliance the first qualified electrician fitted, saying it was wrong and wouldn't last. Therfore, I turn to gain a consensus somewhere for assurance... thanks again for the advice from everyone.

 

[Vortigern]

I tend to liken this to a commuter travelling a hundred miles each day to and fro for work. He can drive a fiat 500 or a nice two litre car. The strain on a 500 cc engine would wear the engine much faster than a 2l engine. Hence I would at least fit 6mm² cable for the longevity ensured.

 

[Intoelectrics]

All appears to be fine and the circuit safe to use, assuming the installing electrician is accurate with the details of the cable run, installation method, diversity and de-rating factors.

Me personally, though the diversity applied is fine, I always feel (and this is just my personal opinion not a professional judgement) that for cookers it can often seem a bit low. I understand and accept that maybe for general day to day use this would work perfectly fine. But still I would most likely either be a little more over cautious and go a size bigger than what calculates or ask the client what the likelihood of the cooker being used more than general is.

For example a good friend of mine's wife is an avid baker and spends many days in the kitchen baking, cooking probably much more than most normal households. In this scenario she would more than likely use much more than the applied diversity factor predicts.

At the end of the day Chris its your call, the circuit installed by all accounts calculates fine for intent and the installing electrician has provided evidence to suggest this.

 

[Gc1971]

Hello all.
I'm the first guy.
I couldn't fit the oven not because I refused to but because I was on holiday.
Are those saying you need 6mm on a clipped direct no derating factor 32a circuit saying they disagree with the iet table? I'm not trying to be argumentative, I'm just following the book. Surely the iet have checked these as a long term load.
Cheers
Gc