Induction Hob - what is the maximum rated power hob I can install in conjunction with a with a 3.5KW oven on a 32A cooker circuit?

[P drop]

Hi, first post!!!
Ive looked at other posts, some 8 or 9 years old when induction hobs were smaller and lower power. Modern hobs appear to have higher power features eg boost, ring bridging etc. I am hoping to install a typical 5 ring (80 to 90cm), typically rated 9 to 11KW.
I wish to replace the existing separate electric oven and electric ring hob with a new electric oven and new induction hob. I have the new oven, rated at 3.5KW. I have not bought the induction hob, hence the question,...what would be the max rated induction hob that can be fitted? The existing "cooker" circuit has a 32A CB, and the current hob and oven are fed from one switch by separate 6mm T&E.
I am hoping to fit a new 45A DP cooker switch, feeding a double outlet plate with 6mm T&E and then running 6mmT&E each to the new hob and oven locations. Some finer points.....
1. The existing cooker switch is midway between the new hob and oven locations, about 2metres cable to each. It has a single socket which I would like to keep, but not essential.
2. Would upgrading the 32A CB (to say 45A) be an option. Replacing the cooker radial circuit wiring is not an option.
3. I understand DIVERSITY allowance could permit the hob max rating I wish (ref Appendix A of the IET's OnSiteGuide) but it would appear diversity requires a certain amount of assessment which the local jobbing electrician may be reluctant to apply (or am I doing them a dis-service, sorry).
4. For clarity, what aspects of my "project" would require installation / certification by a qualified electrician?
I am a retired aircraft engineer, so quite conversant with the technicalities but lacking the knowledge of domestic wiring regulations.

So, in conclusion, what is the max rated induction hob I can pair with a 3.5KW twin oven on a 32A cooker circuit. If not, what are my options (please dont say a smaller hob!!)

Oops , rather a long question, sorry

 

[pete01]

You can have upto 15kw in total on a 32a mcb, some even say 20kw but your 3kw oven and 11kw are inside the 15kw anyway.

 

[EFLImpudence]

Yes, 15kW with socket on switch and 20kW without that socket.

 

[P drop]

Many thanks for your quick, and especially positive unequivocal responses. As a career engineer I really appreciate black and white solutions especially to the application of regulations! One final thing, do regulations (in England) require this installation to be connected or certified by a certified electrician?

 

[EFLImpudence]

One final thing, do regulations (in England) require this installation to be connected or certified by a certified electrician?

No, anyone is allowed to do it.

However that person should do the same as an electrician would/should do regarding testing, certifying etc.

 

[morqthana]

Re the "assessment" of an electrician - ask if he uses an induction hob, and if so, ask him what happens to the contents of a pan sitting on a "ring" running at anything over about 1500W for any length of time. Apart from bringing pans of water to the boil (a kettle is better anyway), you just can't use them at full power.

 

[P drop]

PROBLEM ! I had a local electrician look at the installation and I asked if he would certify my proposed induction hob. He would not. His recommendation, ie what he was wiling to do, was to run an additional 10mm-wired circuit from the CU dedicated to the induction hob, and use the existing 32A cooker switch just for the 3.5kV oven. As the CU has no remaining space, it would require an additional one. The 10mm wiring run would be some 20 to 25m long - I await the quote. This appears to be gross over-kill.

I am confused. The IET is the authority for Wiring Regulations/BS7671:2018, including inspection and certification etc. It is also publishes the Onsite Guide (OSG) "an essential guide for quick reference of information on BS 7671 (The IET Wiring Regulations)". Appendix H4 covers standard cooker circuits, but Appendix A TableA2 clearly specifies a diversity allowance for cooking appliances in household installations. Hence, the OSG's diversity allowance would allow my proposed induction hob and oven on the existing 32A cooker circuit.

So why is an electrician permitted to ignore the IET's guidance and sell a customer an over-inflated solution "just to be safe" and "cover his own arse" (my words)? As an aircraft design engineer I had a multitude of regulations to meet....the important word here being "meet" not "exceed". For instance, if I proposed to fit a heavier gauge wire than required, "to be extra safe" it would be rejected. Extra wire is extra weight and extra cost and reduced performance.
Can electricians be reported for this?

 

[endecotp]

I am a retired aircraft engineer,

PROBLEM ! I had a local electrician look at the installation

Why? You’re much smarter than them. Just get on with it.

and I asked if he would certify my proposed induction hob.

Don’t waste your time. Just do it.

 

[EFLImpudence]

Agreed.

Or find an electrician who knows what he is doing or doesn't just want to rip you off.

 

[pete01]

Can electricians be reported for this?

Doubtful you'd have to report 75% of them

 

[morqthana]

So why is an electrician permitted to ignore the IET's guidance and sell a customer an over-inflated solution "just to be safe" and "cover his own arse" (my words)?

Ask him.

In writing. (With more professional language)

.
Can electricians be reported for this?

You can complain to NICEIC, or ELECSA, or whoever he belongs to.

If he has a social media presence you can take to that and criticise him.

If you see him advertising you can complain to the local paper/church newsletter/whatever.

I doubt any of it will do any real good, but it might make you feel better and it might **** him off.

 

[P drop]

Wow, I can tell there is some contention over this ! Actually, I found him on Checkatrade. He has been the only one to respond to my job in which I stated I was replacing an old oven/hob with a 3.5kW oven and an induction hob, but needed advice on what max power hob he could fit could before I buy. Regarding "just do it". Yup, I now intend to...but as I understand it I may encounter problems when selling the house or invalidating insurance with an inspection certificate.
I do intend to contact the IET and ask them what stops electricians over-quoting for unnecessary work. I now note the IET website has similar discussions on the size of induction hobs on traditional 32A cooker radial circuits.

 

[pete01]

Wow, I can tell there is some contention over this ! Actually, I found him on Checkatrade. He has been the only one to respond to my job in which I stated I was replacing an old oven/hob with a 3.5kW oven and an induction hob, but needed advice on what max power hob he could fit could before I buy. Regarding "just do it". Yup, I now intend to...but as I understand it I may encounter problems when selling the house or invalidating insurance with an inspection certificate.
I do intend to contact the IET and ask them what stops electricians over-quoting for unnecessary work. I now note the IET website has similar discussions on the size of induction hobs on traditional 32A cooker radial circuits.

You could try and educate him, maybe he's a good sparky who doesn't have loads of experience...show him this thread...maybe?

 

[flameport]

additional 10mm-wired circuit

This appears to be gross over-kill.

It is.
Whole houses are connected with that, or even smaller in some cases.

but as I understand it I may encounter problems when selling the house or invalidating insurance with an inspection certificate.

You won't.

In the event of any sale, some electrical documents may be asked for - the answer is that they are not available, which is the answer given in the vast majority of cases.
Even where such things did exist, they are usually lost or destroyed.

The other question which is usually asked is whether any electrical work has been done in the last 20 years or so, and the answer to that is yes.

Insurance companies do not care about documents for the installation of ovens or anything else.
Theoretically possible they might want a copy of a recent EICR after the house burned down, but even then it's unlikely, and most domestic properties don't have one of those anyway.

 

[morqthana]

But are appliances covered by inspection certificates anyway? Surely they only concern themselves with the house wiring?