Induction Hob and Double Oven Diversity

[mpb]

Could someone just check my maths and thinking please.

Induction Hob 7.2kw = 7200/230 = 31.3 A
Double Oven 6.6kw = 6600/230 = 28.7A

Total Load = 60A

Apply diversity

10A + 30% of remaining load

60 - 10 = 50 x 30% = 15A

Diversivified load = 10 + 15 = 25A

So a 6mm T&E on a 32A MCB will be ok

Many thanks

Martin

 

[telectrix]

right in my book.

 

[Farmelectrics]

Why not run 2 supply's

 

[Dave OCD]

I'll second that.

 

[cprfenom]

Would you apply diversity to both appliances individually?

Also I know some suppliers of induction hobs/ovens say no diversity allowed? (Neff is one I know of)

Personally I would run 2x supplies

 

[Darkwood]

Are you just practicing here or are you designing a circuit?

The reason I ask is we use diversity in domestic realm to calculate the overall demand of the complete installation, to put diversity on final circuits would need knowledge of when the loads may exceed a calculated diversified value and the length of time this would occur...

As an oven is a fixed load it can be on for 10mins before the stat level is reach and it switches the elements on and off...I wouldn't apply any diversity here.
The hob has a more flexible diversity but again it can be the case that you have 4 pans on all been heated up together before the stats start to control the load ..again IMHO I wouldn't apply any diversity when gauging the cable size and mcb.

 

[mpb]

Thanks for your replays.

Its an existing kitchen that the gas hob has failed, so they are looking at upgrading to an induction hob and there's already a 6mm to the oven, so they are looking for the cheapest solution.

 

[Andy78]

What does the installation literature for each appliance state ?

 

[mpb]

They haven't purchased the induction hob yet and the oven is approx 10 years old.

 

[Darkwood]

I would go with induction hob and gas oven, that way a power cut still allows food to be cooked plus the electric hob reduces the risk of fire as the oven has a contained controlled flame.

But as in my post 6 .. whichever way go - don't apply diversity on your cable and mcb ratings or you may get a call out on xmas day because they lost power while roasting the turkey.

 

[Andy78]

They haven't purchased the induction hob yet and the oven is approx 10 years old.

Be sure to check the installation requirements for any hob that is to be purchased then. 13A induction hobs are available too.
I was doing an EICR the other day and a 4 minute phonecall to the manufacturers confirmed the full kW rating and connection requirements of a 17 year old obsolete oven.

 

[davesparks]

Are you just practicing here or are you designing a circuit?

The reason I ask is we use diversity in domestic realm to calculate the overall demand of the complete installation, to put diversity on final circuits would need knowledge of when the loads may exceed a calculated diversified value and the length of time this would occur...

As an oven is a fixed load it can be on for 10mins before the stat level is reach and it switches the elements on and off...I wouldn't apply any diversity here.
The hob has a more flexible diversity but again it can be the case that you have 4 pans on all been heated up together before the stats start to control the load ..again IMHO I wouldn't apply any diversity when gauging the cable size and mcb.

I'm not sure if it's been removed from the current regs, but in older editions diversity was not allowed to be used for the calculation of any final circuit except those supplying cooking appliances.

 

[Darkwood]

I'm not sure if it's been removed from the current regs, but in older editions diversity was not allowed to be used for the calculation of any final circuit except those supplying cooking appliances.

I agree in the OP's situe' hence my advice but diversity is often applied in other realms like industrial... the start/up currents for motors are known and usually short lived so cables need not be increased for the start up currents which may be several times higher than the CCC of the cable feeding them, but as the current is only for a few seconds at most the heating effect on the conductors has no negative effects on the integrity of the conductor or insulation. When motor start up curves are longer like for high inertia loads then larger cables may be needed to compensate.

 

[mpb]

Thank you all for the advice. I've decided to quote the customer for a dedicated feed to the hob.

many thanks

Martin

 

[HandySparks]

Current regs 311.1 say "...In determining the maximum demand of an installation or part thereof, diversity may be taken into account.

This is the only para listed in the index under "Diversity". Anyone know of any other references?

The current On-Site Guide lists the formula for diversity of cooking appliances shown by the OP, in Appendix A.

I'm in exactly the same situation as the OP's customer. Old gas hob adjacent to an electric double oven on a 6mm² 32A circuit and fancy changing to an induction hob.

I'm not going to be adding another circuit. I'd be very surprised if a 32A MCB is too small. If it trips, I'll consider changing it to a 40A (subject to Zs being OK). There's no insulation along the cable run and 6mm² T&E is good for 47A with installation method C, clipped direct or buried in an ordinary block wall.