Kitchen Circuits

[askman]

I'm having a new kitchen in the near future and want to understand the electrical side of the installation before I get an electrician involved so that I’ve got decent idea of what to expect.

I’m going to be having the following and have either got their specific loads, or one of a similar appliance where I can’t find the information:

Combi microwave / grill - 10A
Electric oven - 13A
Induction hob - 33.1A
Hood - 1.4A
American fridge freezer - 3.5A
Washer / dryer - 10A
Dishwasher - 6.5A
Only the hood and hob come without a plug.
I will also have normal ancillary appliances - kettle, toaster, etc. plugged in to sockets.

I’ve read that appliances over 2kW are recommended to have a dedicated circuit, however this would put the microwave, oven, hob, and washing machine on individual circuits, which a) seems overkill, and b) pushes my board beyond capacity.

Taking some diversity into account as it’s very unlikely that everything will be running full whack together, would it be reasonable to request the following:

A 6mm radial on a 32A MCB serving a fused spur for the hob
A 6mm radial on a 32A MCB serving a fused spur each for an unswitched single socket to the oven and microwave
Everything else picked up, including sockets, on a 2.5mm ring from a 32A MCB

Could the hob and oven share a 6mm / 32A radial and have the microwave on the ring?

Cables will run in the floor above and will be - approx. 10m for the radials with around 3m of this through insulated flat roof space, and the ring would likely be around 40m including all the drops from the ceiling, with approx. 10m in the insulated flat roof.

 

[EFLImpudence]

Combi microwave / grill - 10A

Plug in anywhere.

Electric oven - 13A
Induction hob - 33.1A
Hood - 1.4A

That's not much - normal cooker circuit would do; see below.

American fridge freezer - 3.5A
Washer / dryer - 10A
Dishwasher - 6.5A

Normal 32A circuit will be fine; see below.

Only the hood and hob come without a plug.

The hood is irrelevant. The oven can be lugged in to the general circuit or the cooker circuit.

I will also have normal ancillary appliances - kettle, toaster, etc. plugged in to sockets.

They can be plugged in to the general circuit.

I’ve read that appliances over 2kW are recommended to have a dedicated circuit.

Not true - anyway, dedicated does not mean separate; just designed properly.

however this would put the microwave, oven, hob, and washing machine on individual circuits, which a) seems overkill, and b) pushes my board beyond capacity.

No. It does not mean that.

Taking some diversity into account as it’s very unlikely that everything will be running full whack together, would it be reasonable to request the following:
A 6mm radial on a 32A MCB serving a fused spur for the hob

Yes, 4mm² will be adequate unless the cable runs through thermal insulation.

A 6mm radial on a 32A MCB serving a fused spur each for an unswitched single socket to the oven and microwave

If you want a separate circuit for them then 16A/20A 2.5mm² (subject to installation method; e.g. thermal insulation) will be more than adequate.

Everything else picked up, including sockets, on a 2.5mm ring from a 32A MCB

Yes - or 4mm² radial depending on actual route and installation method.

Could the hob and oven share a 6mm / 32A radial and have the microwave on the ring?

Yes. as above for 4mm². Although 6mm² will likely be used because that's what people do because that's what people do.

Cables will run in the floor above and will be - approx. 10m for the radials with around 3m of this through insulated flat roof space, and the ring would likely be around 40m including all the drops from the ceiling, with approx. 10m in the insulated flat roof.

Do not run the cables through or covered by the insulation then. If unavoidable then you will require larger cables.

 

[ban-all-sheds]

And if you have a flat roof abandon any plans, if you have them, for recessed lights in the ceiling.

 

[askman]

Plug in anywhere.


That's not much - normal cooker circuit would do; see below.


Normal 32A circuit will be fine; see below.


The hood is irrelevant. The oven can be lugged in to the general circuit or the cooker circuit.


They can be plugged in to the general circuit.


Not true - anyway, dedicated does not mean separate; just designed properly.


No. It does not mean that.


Yes, 4mm² will be adequate unless the cable runs through thermal insulation.


If you want a separate circuit for them then 16A/20A 2.5mm² (subject to installation method; e.g. thermal insulation) will be more than adequate.


Yes - or 4mm² radial depending on actual route and installation method.


Yes. as above for 4mm². Although 6mm² will likely be used because that's what people do because that's what people do.


Do not run the cables through or covered by the insulation then. If unavoidable then you will require larger cables.

So for clarity - 32A radial for hob, oven and hood in 6mm due to having to go through the insulation, and 32A ring in 2.5mm for everything else?

 

[askman]

And if you have a flat roof abandon any plans, if you have them, for recessed lights in the ceiling.

What makes you say that? Recessing into the thermal insulation, i.e. lack of airflow for dissipation of heat?

 

[ban-all-sheds]

Sorry - I should have said if you have a cold deck flat roof abandon any plans, if you have them, for recessed lights in the ceiling.

 

[EFLImpudence]

So for clarity - 32A radial for hob, oven and hood in 6mm due to having to go through the insulation,

Through means completely surrounded. Do not do that you will need 10mm². Under more than 100mm. the same.
Under 100mm or less, alright.

Is there no way to avoid the insulation? Run on top, clip to joists, run somewhere else ???

and 32A ring in 2.5mm for everything else?

If a ring is the better choice, yes.

 

[askman]

Through means completely surrounded. Do not do that you will need 10mm². Under more than 100mm. the same.
Under 100mm or less, alright.

Is there no way to avoid the insulation? Run on top, clip to joists, run somewhere else ???


If a ring is the better choice, yes.

Possibly. The issue will be that the insulation is in the ceiling void of a full width, flat roof extension and all the appliances sit under it.

It might be possible to drop the cable within a boxed in section that will surround a column, run below the level of the work surface, and back up via chases to the spurs, thereby missing the insulation completely...

 

[flameport]

I’ve read that appliances over 2kW are recommended to have a dedicated circuit,

Not true, and never was.

The 2kW deal is found in an appendix of BS7671, and is not a regulation or requirement.
It's applicable to ring final circuits only, and is one of four suggested methods of ensuring that a ring circuit has the load distributed rather than being concentrated at a single point.
The actual item states:
'connecting cookers, ovens and hobs with a rated power exceeding 2kW on their own dedicated radial circuit'
which in most cases they already will be, a separate circuit for cooking appliances is a standard item found in most homes.

The regulation it refers to is 433.1.204, which applies to ring final circuits of 30A or 32A only, and that requires 'under the intended conditions of use, the load current in any part of the circuit is unlikely to exceed for long periods the current carrying capacity of the cable' - no reference to 2kW or any other power ratings or types of appliance.

Taking some diversity into account as it’s very unlikely that everything will be running full whack together,

That is exactly the point, and the actual load is usually far less than most people imagine, even for things like electric hobs.

Washing machines and dishwashers only heat water for a small percentage of the operating cycle - the rest is a low powered motor / pump.
Fridges are only on for a small percentage of the time. Ovens / hobs / cookers do not have all of the elements on all of the time, and induction hobs typically use far less energy than more traditional heating element types.

All the other stuff such as kettles, toasters and microwaves is used for such short periods that it's almost irrelevant.

 

[ban-all-sheds]

Possibly. The issue will be that the insulation is in the ceiling void of a full width, flat roof extension and all the appliances sit under it.

Ah - so it is a cold deck.

And if you have a flat roof abandon any plans, if you have them, for recessed lights in the ceiling.

What makes you say that? Recessing into the thermal insulation, i.e. lack of airflow for dissipation of heat?

You'd need to cut holes in the insulation for recessed lights - that's a no-no.

But the cables won't run through the insulation, surely? Won't they be on top of the ceiling, under the insulation?

 

[askman]

Ah - so it is a cold deck.


You'd need to cut holes in the insulation for recessed lights - that's a no-no.

But the cables won't run through the insulation, surely? Won't they be on top of the ceiling, under the insulation?

It is a cold deck, yes. Although I do want to upgrade to warm deck in future - not that that will resolve the downlighter issue in the short term...

I plan on using blanket type insulation as I have some left over from when I did my loft so I could potentially use covers for the lights (which will be LEDs - certainly not heatless but cooler than halogens) and sit the insulation on top of these, albeit that I'd have to do something clever to fix the covers in place before the plasterboard goes up and then find the exact right spots...

As for the cables, you're right, they would go beneath the insulation. In theory they could even go in first so that they sit on top where it'll be cooler for the most part.