Diversity and induction hobs

[Pretty Mouth]

I recently had a discussion with another spark about induction hobs and diversity.

He pointed out that an induction hob may have, for example, 4 X 3.2kW cooking zones (total 12.8kW), but due to internal power management, the appliance could never draw more than say 7.2kW, that being shared among the zones in use. His view is that the limited maximum, in this example 7.2kW, should be the design current for the circuit, and no diversity can be applied as the maximum could easily be reached.

My conflicting view is that diversity can be applied, but should use the sum of all elements (in this example 12.8kW) for the calculation. My logic is as follows:

Take another hob, identical ratings, but this time not an induction hob, and with no power management to limit the maximum load. After diversity, it is expected to pull 24A although in theory it could pull 56A if all elements are on full simultaneously.
Compare this to the induction hob - again after diversity it would be expected to pull 24A, but due to power management could only pull a maximum of 31A, even if all zones are on full whack at the same time.

What are the views and experiences of other members of the forum on the subject?

 

[Taylortwocities]

It depends on the induction hob. I have a 5 zone Neff induction hob. It provides a power boost function to provide a fast heat function. It is limited so that only two zones can have the boost function at any one time.
if I were doing a diversity calculation I would add 2xboost currents added at the end.

but in practise, if Neff says it needs its own 32A supply then that’s what it gets.

 

[Midwest]

You also have to consider how the product is used by the end user. I hardly ever use my hob with all zones heating, and never apart from initial start up, have them on full power. The ones that are on, are just cycling on & off. Think thats another part of the concept of diversity.

In my old place we had a range cooker (can't remember its total max load). The manufacturer stated it need a 40A supply. You could have three ovens running at the same time. When I clamped metered it, could never get more than 14A.

 

[telectrix]

In my old place we had a range cooker (can't remember its total max load). The manufacturer stated it need a 40A supply. You could have three ovens running at the same time. When I clamped metered it, could never get more than 14A.

t you should have put a few more shillings in the meter.

 

[Wilko]

Hi PM - Using the larger load management value removes the estimation of end user behaviour that is implied by domestic diversity calcs, so that would be my preference. As you’ve shown there may not be a lot of difference and hopefully the load management value would still fit within the usual conductor sizes.

 

[Pretty Mouth]

Thanks for your comments all. @Midwest , good idea to measure the current drawn by your oven with a clamp meter, and interesting that it came out so low. If I ever get the opportunity I'll do the same with an induction hob with all zones on full, be interesting to see what current they actually pull.

 

[Midwest]

Thanks for your comments all. @Midwest , good idea to measure the current drawn by your oven with a clamp meter, and interesting that it came out so low. If I ever get the opportunity I'll do the same with an induction hob with all zones on full, be interesting to see what current they actually pull.

Do. I'd like to help and clamp my current ceramic hob, but my clamp meter went whibble ages ago.

To the annoyance of some here, getting new smart meters soon, so might be able to report back then.

 

[telectrix]

Do. I'd like to help and clamp my current ceramic hob, but my clamp meter went whibble ages ago.

To the annoyance of some here, getting new smart meters soon, so might be able to report back then.

buya new clamp meter, tight arse.

 

[Midwest]

buya new clamp meter, tight arse.

Can't be arsed, as I have no use for now.

 

[Markyd]

Manufacturers instructions end of

 

[richy3333]

Can't be arsed, as I have no use for now.

of course you have a use for one, to answer @Prettymouth question

 

[Andy78]

Manufacturers instructions end of

This is also my view. I have seen hobs that only ever pull though one element at a time and ones that can have all 4 on at once. Diversity has no place in connecting such appliances.

 

[HappyHippyDad]

Some interesting responses.

I have recently fitted a huge range cooker which had an electric hob. I worked out the max demand using the OSG diversity and it 'just' crept into using a 6mm cable. However the MI clearly said 50A supply with a 10mm cable. The 6mm on an appropriate MCB would have been fine but after being clearly told by the manufacturer that it needed a 10mm cable that was the right option.

I don't think it's always a case of 'manufacturers instruction, end of' though. That means we are not using our electrical knowledge and are just following blindly what someone else says. I haven't seen many 3A fuses for an extractor fan supply which most MI state.

 

[Markyd]

Well if you were using your electrical knowledge you would know that in the regs it says that manufacturers instructions must be followed even if they differ to the blue book itself

 

[Andy78]

Well if you were using your electrical knowledge you would know that in the regs it says that manufacturers instructions must be followed even if they differ to the blue book itself

It says they must be taken into account. We have freedom to exercise our engineering judgement.
The blue book says we must select equipment according to it's suitability.

 

[Markyd]

Depends what part you read
VERIFICATION OF ELECTRICAL INSTALLATIONS
134.1 Erection
Regulation 134.1.1Good workmanship by competent persons or persons under their supervision and proper materials shall be used in the erection of the electrical installation, Electrical equipment shall be installed in accordance with the instructions provided by the manufacturer of the equipment.

 

[Andy78]

Depends what part you read
VERIFICATION OF ELECTRICAL INSTALLATIONS
134.1 Erection
Regulation 134.1.1Good workmanship by competent persons or persons under their supervision and proper materials shall be used in the erection of the electrical installation, Electrical equipment shall be installed in accordance with the instructions provided by the manufacturer of the equipment.

My blue book says this, and so did my yellow one. You have quoted from an earlier version of the regs.

 

[Midwest]

Some interesting responses.

I have recently fitted a huge range cooker which had an electric hob. I worked out the max demand using the OSG diversity and it 'just' crept into using a 6mm cable. However the MI clearly said 50A supply with a 10mm cable. The 6mm on an appropriate MCB would have been fine but after being clearly told by the manufacturer that it needed a 10mm cable that was the right option.

Was that a Rangemaster? I had a similar thing.
[automerge]1583153796[/automerge]

My blue book says this, and so did my yellow one. You have quoted from an earlier version of the regs.

‘Twas in the green one that said, ‘shall be installed in accordance with’, I believe.

 

[HappyHippyDad]

My blue book says this, and so did my yellow one. You have quoted from an earlier version of the regs.

View attachment 56101

Yes he has, I read the new regulation (new with Amd 3 of the 17th) slightly different to the old. Now we have to take the MI into 'account' which I read as the electrician having more of a choice rather than sticking rigidly to the MI as in the older regs that @Markyd has quoted from.

Was that a Rangemaster? I had a similar thing.
[automerge]1583153796[/automerge]
‘Twas in the green one that said, ‘shall be installed in accordance with’, I believe.

Yes, I think it was a rangemaster, a beast! The first time I have had to use 10mm for a cooker!

 

[Markyd]

ok boys let me have it....didnt have my blue book with me so looked it up on IET forum...should have checked the date...2013.....big schoolboy error waiting for some stick

 

[picturevalve]

Do you have to take into account any failure of the hob power management?
Is any such failure "failsafe"?
Bet it isn't in the manufacturer literature.

 

[Pretty Mouth]

This is also my view. I have seen hobs that only ever pull though one element at a time and ones that can have all 4 on at once. Diversity has no place in connecting such appliances.

Do you think that is the case for all hobs, or just induction hobs?

 

[Wilko]

Do you think that is the case for all hobs, or just induction hobs?

My take is the induction hob has the potential to require a significant circuit upgrade if replacing a ceramic hob. To avoid adding a series buyer resistance (sorry) they’ve invested in the power management to bring it back to a “normal hob” maximum load.

 

[Andy78]

Do you think that is the case for all hobs, or just induction hobs?

I'd make the connection instructions my first reference on any electric hob ime.