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

 

[timhoward]

The most important thing by far is to consult the manufacturers instructions. Do you have a link to the appliance please?

The backup plan is to do a diversity calculation according to the On Site Guide which basically works on the principle that unless you simultaneously turn all the hobs and ovens on together you won't draw the total rated power. Once on they all have their own thermostats and turn on and off when needed, so again you won't draw the maximum rated power. Some modern appliances have internal ways to limit this too.

My prediction is the instructions will agree with the 2nd electrician and the calculation will agree with the first electrician (regarding breaker size alone). The manufacturers instructions always take precedence though.

(There is a further concern with the 4mm cable and a 32A breaker but this might prove to be immaterial. )

 

[Rockingit]

I had this scenario years ago with Aga (it may even be a thread on here..) The customer was having a new Induction Range fitted directly by AGA, their installer was insisting on something ridiculous like a 16mm feed, customer called me in to fit one. Wasn't an option practically so began the dispute with Aga technical that actually they didn't understand diversity and that the existing 6mm/32A feed would suffice. Went on for days and days before Aga finally conceded that I was correct and to go ahead and fit on a 6/32. That was years ago - never heard back with a problem from the client!

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

 

[Chris C300]

The most important thing by far is to consult the manufacturers instructions. Do you have a link to the appliance please?

The backup plan is to do a diversity calculation according to the On Site Guide which basically works on the principle that unless you simultaneously turn all the hobs and ovens on together you won't draw the total rated power. Once on they all have their own thermostats and turn on and off when needed, so again you won't draw the maximum rated power. Some modern appliances have internal ways to limit this too.

My prediction is the instructions will agree with the 2nd electrician and the calculation will agree with the first electrician (regarding breaker size alone). The manufacturers instructions always take precedence though.

(There is a further concern with the 4mm cable and a 32A breaker but this might prove to be immaterial. )

The most important thing by far is to consult the manufacturers instructions. Do you have a link to the appliance please?

The backup plan is to do a diversity calculation according to the On Site Guide which basically works on the principle that unless you simultaneously turn all the hobs and ovens on together you won't draw the total rated power. Once on they all have their own thermostats and turn on and off when needed, so again you won't draw the maximum rated power. Some modern appliances have internal ways to limit this too.

My prediction is the instructions will agree with the 2nd electrician and the calculation will agree with the first electrician (regarding breaker size alone). The manufacturers instructions always take precedence though.

(There is a further concern with the 4mm cable and a 32A breaker but this might prove to be immaterial. )

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

 

[Chris C300]

I had this scenario years ago with Aga (it may even be a thread on here..) The customer was having a new Induction Range fitted directly by AGA, their installer was insisting on something ridiculous like a 16mm feed, customer called me in to fit one. Wasn't an option practically so began the dispute with Aga technical that actually they didn't understand diversity and that the existing 6mm/32A feed would suffice. Went on for days and days before Aga finally conceded that I was correct and to go ahead and fit on a 6/32. That was years ago - never heard back with a problem from the client!

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

Thanks, good to know. But there is nowhere I can see confirming 4mm will be enough

 

[Rockingit]

Thanks, good to know. But there is nowhere I can see confirming 4mm will be enough

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.

 

[timhoward]

The calculation comes out at 28A if ordinary isolator and 33A if there's a socket on the isolator. So the email makes sense to me

Thanks, good to know. But there is nowhere I can see confirming 4mm will be enough

Sorry, we can't give you a definite yes over the internet.

The cable rating depends on it's route, length, what is passes through, and how it's attached. Clipped direct to a surface it's higher rated than floating in middle of insulation or in conduit. 4mm rating can be as low as 17.5 amps and as high as 36 amps.

The entire circuit design has to be sufficient for the load (32A is ok for 28A load but more headroom is definitely better).
The breaker has to rated at less than the max cable rating (32A is only < cable rating in the scenario it is clipped direct; 32A > cable rating in every other scenario).
The max cable rating has be be sufficient for the load (definitely at upper limit in most of the scenarios, insufficient in other scenarios)

So it's certainly all a bit tight. But we can't say what is there is definitely wrong.
(My biased arrogant opinion is that 4mm was a slightly daft and inflexible choice - but that doesn't help you.)

 

[Rockingit]

(My biased arrogant opinion is that 4mm was a slightly daft and inflexible choice - but that doesn't help you.)

Agreed!! Given the pence difference it would have been. I think if I went back to doing domestic new-build again [shudder], I'd be laying in 10mm for cookers and showers as a default.

 

[brianmoooore]

In this particular case, it looks like both electricians might be wrong. 4mm2 is pushing the limits one way, and 10mm2 with 45A fusing is over the top the other.
6mm2 on 32A would be fine (installation method dependant), but as Rockingit wrote above, if I were changing it, I'd lay in 10mm2.

 

[Chris C300]

In this particular case, it looks like both electricians might be wrong. 4mm2 is pushing the limits one way, and 10mm2 with 45A fusing is over the top the other.
6mm2 on 32A would be fine (installation method dependant), but as Rockingit wrote above, if I were changing it, I'd lay in 10mm2.

Hi, thanks everyone for your comments

In this particular case, it looks like both electricians might be wrong. 4mm2 is pushing the limits one way, and 10mm2 with 45A fusing is over the top the other.
6mm2 on 32A would be fine (installation method dependant), but as Rockingit wrote above, if I were changing it, I'd lay in 10mm2.

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.

 

[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

 

[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

 

[timhoward]

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

First of all welcome! I hope the above doesn't make too painful reading - there are certainly gentler ways to join a forum!

There were some early responses before the fact it was clipped direct came to light. After that I think there was a consensus that it was compliant and you'd done nothing wrong(!).
It's true that a few of us (myself included) did express some surprise mainly because it's not something we encounter too often.

 

[DPG]

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

Welcome to the forum!

 

[mattg4321]

Can’t believe some here are advocating 10mm for domestic cookers. Absolutely no need unless it’s run through mountains of insulation making 6mm on a 32A OCPD non compliant.

Never known any domestic cooker to require more than 32A and I’ve had this argument many many many times before.

10mm for showers is another story. That I totally agree with.

 

[brianmoooore]

Shower is a known fixed load (often less than initially expected if the rating of the shower is declared at 240V), and is not normally used for more than about 5 minutes at a time by normal people.
A cooker is an extremely and constantly varying load, for which we use a diversity formula to give the long term average maximum load. At times, the load will be well over that diversified current, and well above the rating of a 32A OCPD for hopefully short periods. For these reasons I would not use a 4mm cable for a cooker such as this.
At today's prices, the difference between 4mm2 and 6mm2 is 58p/m, so on a 15m run, would only have made a difference of less than £9 to the cost of the job.

 

[nicebutdim]

Shower is a known fixed load (often less than initially expected if the rating of the shower is declared at 240V), and is not normally used for more than about 5 minutes at a time by normal people.

Perhaps you could educate people under the age of 30 on appropriate use of a shower. 20 minutes or more wouldn't be abnormal for many.

 

[mattg4321]

The shower is a fixed load until a plumber changes it for a 10kW one!

Most have cable runs through insulation as they are invariably run through lofts. This is not so for cookers.

I’ve clamped many a cooker and even with a large range cooker it’s surprisingly difficult to get over about 30 amps.

When you clamp showers then it’s almost always around 40 amps with modern units.

A shower is nearly always run at full load whilst a cooker is usually well below its maximum rated current.

Having said the above I would’ve run 6mm probably, although 4mm sounds ok in this case. 10mm is overkill for domestic cookers though. Just not needed.

 

[UNG]

Can’t believe some here are advocating 10mm for domestic cookers. Absolutely no need unless it’s run through mountains of insulation making 6mm on a 32A OCPD non compliant.

You give mountains of insulation as a reason but what about cables run in voids where the ambient temperature with heating pipes that can be at 60ºC+ is never really considered

Never known any domestic cooker to require more than 32A and I’ve had this argument many many many times before.

There are a lot of appliances where the ratings are grossly over what they will run at in normal use, I suppose some of the debate in this thread revolves around a cable that may be close to it's limit and how any future changes in the building fabric may push it over that edge a cable clipped direct could be a cable that is boxed in a few months down the line

While the regs appear to address most of the new technologies it would appear that cooking appliances have been overlooked can we really apply the same diversity to an induction hob as we do to a ceramic or halogen hob when they are using totally different technologies, the induction hobs I have clamped seem very power hungry when compared to the older technologies

10mm for showers is another story. That I totally agree with.

Since the first electric showers came to market at 6Kw the market has gone with bigger Kw's and even bigger Kw's is better and it is more likely you will find burnt cables and switches on shower circuits than cooker circuits

 

[spynage]

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

It will be fine. Should of used 6mm really as best practice, but it's not unsafe if it's fused correctly which it is. Due to the installation method the cable rating may be slightly below 32 amps but as others have said with diversity applied to the cooker your unlikely to use over 32amps anyway. I mean 32amps for cooking is so much! An oven on full power will draw 13amps max but then it will switch off intermittently once up to temperature. Induction hobs do the same with intermittent pulses. You shouldn't have a problem. If the breaker starts nuisance tripping though then you shouldn't ignore this, but I doubt it will happen.

 

[freddo]

Since the first electric showers came to market at 6Kw the market has gone with bigger Kw's and even bigger Kw's is better and it is more likely you will find burnt cables and switches on shower circuits than cooker circuits

Except on modern cookers that use very poor quality terminal blocks! There is such a problem of them melting and catching fire (often on the factory side connections) the manufacturers, instead of going back to proper heavy duty type found in most cookers when I was fitting and repairing them as a job 16+ years ago, are now supplying metal covers that go over the same crappy plastic terminal blocks to contain the fire. Product manufacturers and designers are morons.

 

[UNG]

Except on modern cookers that use very poor quality terminal blocks! There is such a problem of them melting and catching fire (often on the factory side connections) the manufacturers, instead of going back to proper heavy duty type found in most cookers when I was fitting and repairing them as a job 16+ years ago, are now supplying metal covers that go over the same crappy plastic terminal blocks to contain the fire. Product manufacturers and designers are morons.

And now back to the other thread about AFDD's