Domestic Kitchen Advice

[rsmck]

We are installing a new kitchen with the following cooking appliances - Combination Microwave rated at 3.2kW, Oven rated at 3.55kW and Hob rated at 7.2kW making a total of around 60A!

The plan was to supply both the oven and hob from a 45A cooker connection unit with a DP isolator protected by a 45A MCB supplied by 6mm T&E from a consumer unit located less than 1m (on the other side of a wall) however then my better half decided to add the combination microwave to the mix.

The kitchen also has a 4mm2 radial circuit supplying the rest of the worktop 13A outlets (and a single dishwasher) and a dedicated socket (on a non-RCD-protected MCB) for the Fridge/Freezer only.

Would you connect the combi oven into the same connection unit and isolator as the other oven (and hob) or just connect the combination microwave into a normal 13A plugtop and outlet ? Alternatively I suppose could run a second 6mm cable from the 45A MCB to a separate isolator for the two ovens (combi+normal oven) and leave the hob on the other isolator - but whilst I can't find anything which would prohibit this it does seem a bit, well, unusual.

Any advice would be greatly appreciated.

[E2A: I know I had a similar thread a while ago, but the kitchen requirements have changed rather a lot (as have many things!) so it seemed more appropriate to start this one]

 

[dickllewellyn]

We regularly come across this sort of setup now, with induction hobs and two or three different ovens, not to mention coffee machines, warming drawers, wine coolers...

One solution we have started to use often is to run a 10mm submain to the kitchen for the appliances. Stash a little sub board in a cupboard near the appliances, you may be happy with the provision of this sub board for isolation purposes, in which case just wire appliances straight back to it with appropriate OPD for each appliance. Any with plugs on should have a socket outlet so you don't have to remove the plug and invalidate the warranty. Some people may still like to have individual switches for appliances, that's horses for courses!

 

[rsmck]

We regularly come across this sort of setup now, with induction hobs and two or three different ovens, not to mention coffee machines, warming drawers, wine coolers...

Thankfully we stopped before it got to that stage.... but yes, kitchen's electrical requirements have changed rather a lot since this place was originally built (with a single 2.5mm VIR cable going to a cooker switch!)

One solution we have started to use often is to run a 10mm submain to the kitchen for the appliances. Stash a little sub board in a cupboard near the appliances, you may be happy with the provision of this sub board for isolation purposes, in which case just wire appliances straight back to it with appropriate OPD for each appliance. Any with plugs on should have a socket outlet so you don't have to remove the plug and invalidate the warranty. Some people may still like to have individual switches for appliances, that's horses for courses!

I was under the impression individual isolators for appliances (close to the appliance) was a legal requirement but since the ovens were to be on their own circuit from the main consumer unit (which is literally right next to the kitchen) personally I'd be quite happy with that as the isolator (and it's less likely to have things piled in front of it than if i put a sub-board in a cupboard...)

It would also greatly simplify the installation - just have the micro plugged into a socket, a supply from the CU to the cooker connection unit, which in turn feeds the hob and oven.

I still can't quite get over this place had three re-wireable fuses when I moved in ... and that was it

 

[Engineer54]

Here we go again.... When are you guy's going to realise that cooking loads have larger than normal diversity allowances??? The total load here is under 15KW, so in theory they could all be supplied via a 6mm cable and a 32A breaker.... But here we have 3 appliances, one being a combo microwave oven, which in all honesty can go on a 13A plug and socket, because it's never going to take 3.5KW!! The other 2 cooking loads can be fed from the existing Cooker unit, via a twin CCU.


Why does no-one look-up other related threads before they post the self same question that's been answered more than a good few times??


As for suggesting that supplying kitchens with sub main CU's, is the normal way to go, ....absolute rubbish, not unless the house is extremely large, and complete with a Kitchen that could cater for the local rugby team on a daily basis...

 

[rsmck]

I know on paper applying diversity it should be about 26A ... so I figured that 40A would be more than enough (the breaker's there anyway) with a 6mm cable supplying the CCU to which the oven and hob are connected. The combination oven can go on a 13A plug and socket however this would then need its own isolator, no ?

I did wonder if I could simply connect all three to the CCU (since they're in close proximity) but it'd probably be simpler to have the combination microwave oven on a plugtop or fused spur.

The only thing with the diversity rules is, in theory they sound great, in practice I can think of many kitchens where all 4 hobs + both ovens are in use, so I think the 10A + 30% of the remaining maximum is probably a little conservative.

 

[Engineer54]

The only thing with the diversity rules is, in theory they sound great, in practice I can think of many kitchens where all 4 hobs + both ovens are in use, so I think the 10A + 30% of the remaining maximum is probably a little conservative.

You would be Wrong!!! If the total load is 15KW or under, It has been doing just that for over 50 years now!!!

 

[telectrix]

oven and hob on a 40A MCB, 6mm cable to 45A cooker isolator. microwave on it's own radial, 16A MCB, 2.5mm cable, D/P isolator switch or 13A socket. job done.

 

[dickllewellyn]

A lot of these combi microwaves require a dedicated 20A supply. Check the manufacturers instructions as there will almost certainly be a specification.
The idea of running a submain to a kitchen is not the normal way to go, it's a suggestion for when there are a number of appliances with a reasonably high load. We have in the past run multiple 20A radials for each appliance, one kitchen had four ovens. Induction hobs don't have the same diversity calculations as thermal hobs. Add a 3KW under sink water boiling device (no brand names!), a 2.5 KW coffee machine, and all of a sudden a 10mm feeding the lot sounds much better than multiple cables back to consumer unit.

 

[telectrix]

wood fired stove, dolly tub, dishcloth and sink. problem solved. sssimmpllesss

 

[rsmck]

oven and hob on a 40A MCB, 6mm cable to 45A cooker isolator. microwave on it's own radial, 16A MCB, 2.5mm cable, D/P isolator switch or 13A socket. job done.

Not far off the original plan - except with an additional radial for the microwave - will do it that way - thanks telectrix.

Does the microwave still need a DP isolator if it's on its own MCB ? Wouldn't the MCB itself provide suitable isolation?

wood fired stove, dolly tub, dishcloth and sink. problem solved. sssimmpllesss

Brilliant

 

[telectrix]

the MCB would be suitable isolation as per regs. but if not fitting on a plug, i would prefer local isolation as in D/P isolator. the reason for this is, if the appliance had a fault, tripping the RCD, then by isolating at the D/P switch, tghe fault would be removed from the circuit. the MCB can't isolate a N/E fault.

 

[Octopus]

wood fired stove, dolly tub, dishcloth and sink. problem solved. sssimmpllesss

Plus a nice rack for all those take away menus!

 

[telectrix]

and a solution to getting rid of most of the rubbish, now that the bins only get emptied once a fortnight, if it's a full moon and as long as there's not a bank holiday within 3 months.

 

[Voltimax]

one being a combo microwave oven, which in all honesty can go on a 13A plug and socket, because it's never going to take 3.5KW!!

I'd disagree with you there. If it's a NEF they specifically require a 16A circuit as per manufacturers instructions.

 

[Engineer54]

haha!! probably because its German, and that's what they use over there....

If it's 3.5KW, that will be it's connected load, it is not it's true maximum load. I have a Sanyo combo microwave, rated i think at 3.3KW, i think it's maximum loading is more like 2.4KW ...As i said, a plug and socket arrangement!! I wouldn't mind betting that the OPs appliance is also fitted with a 13A plug top too, The same as mine is!!!