Oven and hob diversity

[littlespark]

Morning lads.

Todays job is to go to in laws and firstly replace a cooker hood that went fzzzzz! Which is straightforward.
But I’ve also got to change the gas hob for an electric. Following an incident where gas was left on by increasingly forgetful mother in law.

There is an existing 32A protected, 6mm cable cooker supply switch that controls a double oven at the moment…. Total rated load 4.8kW

The new hob is 5 ring ceramic, rated 7350W

What’s the diversity on a 5 ring hob, and could it share the cooker supply? Even if I update the 32 to a 40. (Old mk sentry board, hoping I’ve got spare mcbs)

I’m all set to run in a new 6mm through the wall into the garage and back to the board… but wanted to save a bit of time with this being a family job.

 

[brianmoooore]

Cooker diversity calculations were framed before the era of separate hobs and ovens, but as long as they're installed oven below hob, as they would be on a conventional slot in cooker, then I'm happy to apply them.
4800W + 7350W = 12150W = 52.83A.
52.83 - 10 = 42.83A. 30% of 42.83A = 12.85A. Adding back in the 10A gives 22.85A design load, so well within the limits of 6.0mm2 and 32A breaker.
Add in another 5A if there's a socket combined with the isolator.

RE: the original gas hob. Left on as in heat causing danger (arguably safer than an electric one, since you can see a gas hob is 'on' from a distance) or the danger from escaping gas? Modern gas hobs should have flame failure devices that cut the gas supply after several seconds of no flame.

 

[littlespark]

This is the layout. I took the back off the drawer unit and can get to the cable. Definite 6.00mm.
Dual oven to left, hob to right.

Can just cut the outgoing 6mm, and joint through with the cooker outlet plate.

Appliance delivery is on its way.






Edit.
Is the diversity calculation the same for 4 and 5 burners?

 

[brianmoooore]

No mention of number of burners, or number of ovens either. The application of the diversity calculation as stated or not is ultimately the responsibility of the circuit designer of course. You wouldn't apply it to a commercial kitchen.

 

[littlespark]

Well, once it’s all up and running, I can clamp the feed at various combinations of ovens, grill, rings… see what I get.

 

[littlespark]

All up and running. Pulling roughly 6A per heating zone on the hob…. But it’s a really clever AEG ceramic hob and shuts off if there’s no pan on the zone.

Also AEG hood, and the two speak to each other. Turn on the hob, the hood lights up…. Any heat zone will turn on a fan, and the higher heat, the faster the fan.

Clever stuff.

 

[Moley]

Clever stuff? Nah, just more to go wrong.

 

[naylorpd]

I know you have to do your diversity calculations in the prescribed way, and that's going to give you a hard result which you can then install.

But for me, in real life, think whether you ever used all 4 (or 5 rings) on a hob, maxed out, at the same time? Even with a 5-ring, the most I can ever recall using is 3 (about the limit of my multi-tasking capability these days...) and very unlikely to be all full on.

 

[bigspark17]

this is when diversity calcs are pointless. If the whole oven and hob is on then you need to accomadate for that because it is possible, most of the time they wont and all ovens and rings have stats so they are not going to be, but this diversity calc is as much of a joke as the maximum demand calc. Then for a laugh youhave to add on 5a if theres a socket on there what the hell does that mean where has that 5amp come from. More than likely it will be the kettle or a toaster plugged in. Rant over