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

[UNG]

Hi thanks for the response. Its a Rangemaster profesional delux induction hob. See link here:

https://www.rangemaster.co.uk/sites/default/files/user_guides_uploaded/U110890-01%20%5BGB%5D_0.pdf

Rangemaster say the following in an email following phone call:
START EMAIL
Good Afternoon,

Thanks for your earlier phone call,

We always recommend ensuring your fitter refer to the users guide before installation.

Ceramic and induction models may be connected to a suitable 6mm cable with a 32-amp breaker (providing the isolator switch, which turns the power on and off to the cooker, does not incorporate a 13 amp socket). Based on *domestic cooker diversity it would not be necessary to upgrade to a 10mm cable / 45 amp fuse, however we would recommend you do so, as it would be better to provide a greater load flexibility. We would recommend that induction cookers are also fitted to a RCBO fuse (Residual Current Breaker with Overload protection).

Please note: These are guidelines and other factors may alter the cable/breaker power. Therefore we cannot provide electrical information as the qualified electrician has to make calculations based on what is around the cooker e.g. boilers etc.
END EMAIL

the electrician is adamant he has done calculation and 4mm is enough.

Thanks again

Looks like you have had a definitive answer from the manufacturer here as others have said for a new installation I would err towards 10mm² cable but wouldn't have a problem connecting to a 6mm² if that was already fitted 4mm² is just a bit too thin for this load

 

[Electro-tech]

This link may be useful to the OP.

 

[davesparks]

In the most perfect of conditions, what I assume to be 6242Y (standard twin and earth) at 4mm is rated for 36A. However, at around lets say a 15m run from your CU to where it's actually running to, you'll lose roughly 6v running at 32A, plus you're also asking the cable to run at the very extreme end of it's 70C rating - it will probably feel very hot to touch and as a consequence probably degrade fairly quickly by comparison to 6mm which is 46A in the same scenario.

A 6V drop is well within what is allowed by the regulations.

The cable is designed to work safely at a conductor operating temperature of 70C, all necessary safety margins have already been allowed for in the tabulated values.

I always find it odd that people will happily install almost any other 32A circuit in 4mm but for cookers they refuse to accept anything less than 6mm

 

[davesparks]

I don't have a book to hand but it doesn't look like anyone has considered rating factors in this thread, bearing in mind they can increase cable ratings in some circumstances.

 

[Rockingit]

A 6V drop is well within what is allowed by the regulations.

The cable is designed to work safely at a conductor operating temperature of 70C, all necessary safety margins have already been allowed for in the tabulated values.

I always find it odd that people will happily install almost any other 32A circuit in 4mm but for cookers they refuse to accept anything less than 6mm

The principle difference is simply time. It's reasonabl to assume that a 32A radial circuit instead of a 32A RFC (for example) will peak/trough all over the place and average out at only a minor % whereas something like an oven will be drawing full whack for some time until it gets to temperature.

I don't have a book to hand but it doesn't look like anyone has considered rating factors in this thread, bearing in mind they can increase cable ratings in some circumstances.

Like this, you mean? "I would say, however, that 4mm is probably cutting it fine once you've actually done the proper de-rating calcs"

 

[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