Cable Diversity for Induction Hob

Diversity calc looks correct to me. I've got a 7.2kW hob running on a 20A circuit at home and has survived quite a few Christmas diners now.


As to whether to use a larger cable to allow for future changes - sounds good to me - but check whether the customer is willing to pay the extra.


  - Andy.

Induction hobs are quite 'weird' compared to traditional resistance heating. The average current is much lower, but the RF generators need filters that give a lot of earth leakage, so perhaps   budget for its own RCBO or RCD or at least have an escape plan if it is needed.


I too would be happier to go up a cable size for expansion - partly because I'm unsure how good the old style calcs are on the newer hobs, and also  it may be that an oven of some sort is added at some point, that may actually need more than the hob by the sound of it.

What do the makers instructions say - or what cable does it come with ?

Mike

Awesome. Thanks for your input?? 

would you say then, as it’s going to be part of a split load/dual rcd consumer unit, it should still be on it’s own RCBO?

The hob may well leak up to 10mA or so, and a '30mA' RCD fires anywhere between 15mA and 30mA,  so it does not leave much allowance for other electronic devices plugged into the ring - computers and monitors etc can clock up  a few mA of earth leakage each, as can the lots of the little switch mode units that supply LED lights instead of traditional transformers and so on.

You may be all right on a shared RCD, but I know a couple of colleagues, admittedly in larger more IT heavy houses, where a dedicated RCBO for the hob was eventually needed as the solution to random tripping.

The RCD may be nearer the upper limit, or it may not, and I cannot see the set-up and how much electronics there is in the house already.


M.

That’s a fair comment. I think just to be on the safe side, I’ll see if they are willing to pay the little extra for a separate RCBO module. Thanks for your knowledge??

No you don't apply diversity to single loads, you apply it to distribution circuits and whole installations.


The circuit protection and cable CSA should meet the demands of the plated current and/or the manufactures specifications in their data sheet.


Of course you can put it on a bit of 1.5mm T&E with a 10A MCB if you like and it will probably be OK for most of the time but then you are not complying with the manufactures instructions see Regulation 134.1.1.


JP

Hi John.

That is true if there is a single heating space, but if there are 4 the situation is a bit different. Essentially to use all 4 at full power draw would need 4 big pans on full at once, which is pretty unlikely. A small pan does not get as much power as one that is larger than the marked space. To get full power the thing being heated must be fully coupled to the hob coil, be thick enough to fully load the induction generator, and generally not be too hot. All of these things lead to less loss in the pan base and consequently reduce the power dissipation and supply current. However, there is not much reason to reduce the cable size upon installation, unless it is an existing one being reused. After all 4mm is not hugely more expensive than 2.5 is it, and then you can fit a 32A MCB/RCBO which will cope just fine when you put a commercial pot on the stove 3 feet in diameter filled with 20 gallons of soup, or equivalent metric measurements. I quite like induction hobs if powerful enough, but I haven't found a shaped one yet which fits an INDUCTION WOK with the same heat as the gas, or the WOK either for that matter. A new market, but 10kW please just like the gas!

Presumably this is a new circuit, so just keep it simple and use 4 mm² cable on a 32 A MCB.


Whether an RCBO can be placed in the existing CU is another matter entirely. If the cable is clipped direct and no plug and socket are involved, do you need additional protection?


As for diversity, this appliance is not a whole cooker, so perhaps OSG is a little out of date?

, so perhaps OSG is a little out of date?

The actual wording (in my old copy at least) is "household cooking appliance" - so would seem to cover.


It seems daft to me to be able to apply the cooker diversity rule to a submain but not to the final circuit it supplies - we'd end up with a smaller cable before the DB than after it.


   - Andy.