Set up for oven + combi?

[newbie24]

Been having a discussion with my electrician on the best way to wire up a new oven and a combi oven/microwave and would appreciate some more input.

There is an existing cooker connection in 10mm t&e with a 32a MCB (and RCD protection).

The oven is 3.49kw and the combi is 3kw. Oven doesn't have a cable with in and the absolute max that fits in the connection is 2.5mm flex. The combi has a 1.5mm flex.

Now I believe the oven could be wired into a cooker switch and from there connected up to the 10mm cable maintaining the 32a MCB as it's a fixed loan appliance.

The combi however has the microwave which I don't believe to be fixed load, the cable size is also quite small at 1.5mm, so I'm not sure this would work in the same way.

So my options seem to be a dual outlet cooker plate connected to the 10mm t&e, then a cooker switch for each appliance and 2.5mm flex to oven and the 1.5mm flex to combi microwave. If I did this I could downgrade the MCB to 20a, I believe the diversity calc for cooking appliances is first 10a + 30% of the remainder, which is just over 15a. Would that be necessary or could I leave it at 32a?

Are there any better options that don't involve running another cable to the consumer unit?

 

[Bidges]

I'd keep it as a 32A circuit, fit a dual cooker connection unit and run 6mm to a 13A fused connection unit where you can hard wire the MWO.

 

[newbie24]

I'd keep it as a 32A circuit, fit a dual cooker connection unit and run 6mm to a 13A fused connection unit where you can hard wire the MWO.

Thanks, I did consider that as an option. Do FCUs always have the 3mm separation required?

The manual for the combi says a fuse between 15 and 20amps, if I did downgrade the MCB so you think I'd get nuisance tripping or would it likely be ok?

 

[Bidges]

Thanks, I did consider that as an option. Do FCUs always have the 3mm separation required?

The manual for the combi says a fuse between 15 and 20amps, if I did downgrade the MCB so you think I'd get nuisance tripping or would it likely be ok?

Most FCU's have the 3mm gap for isolation, but you're just on the limit for a 13A fuse. Seems a shame to downgrade the 32A cooker circuit, but in fairness the likelihood of a 20A breaker tripping 6.5Kw worth of ovens is actually quite low unless you have everything on for long periods.

 

[newbie24]

Most FCU's have the 3mm gap for isolation, but you're just on the limit for a 13A fuse. Seems a shame to downgrade the 32A cooker circuit, but in fairness the likelihood of a 20A breaker tripping 6.5Kw worth of ovens is actually quite low unless you have everything on for long periods.

Thanks, I think that's the route I'm going down. Presumably the load ratings for the combi is oven+grill+microwave, so in reality it's going to be a lot lower than the 3kw rating, and for oven it will be oven+grill, so again you are only going to be running part of 3.5kw. It's a much higher ratio than the 15kw on a 32a MCB...

 

[Steve-S]

Manual for one oven says fuse between 15-20A. What does the manual for the other say?

 

[newbie24]

Manual for one oven says fuse between 15-20A. What does the manual for the other say?

Manual for combi says that, the oven one doesn't specify. I think I'm just going to get 2 new supplies at 16amps each on 2.5mm t&e. Feels like more bulletproof approach. Could put the oven on a 20 but 16 would cover 3.49kw

 

[Steve-S]

Manual for combi says that, the oven one doesn't specify. I think I'm just going to get 2 new supplies at 16amps each on 2.5mm t&e. Feels like more bulletproof approach. Could put the oven on a 20 but 16 would cover 3.49kw

I would keep the cooker cable using that for the 3.49kW appliance changing the breaker to a 20A RCBO. 16A is too low.
2.5mm for the 3kW oven using a 16A RCBO. That would do it.

 

[oscar21]

I've put a 2 way unit inside kitchen cupboards before now if we were re-using the original cooker supply but the customer wanted 2 x 16A ovens.

I know from a safety point of view both ovens would be quite safe on a 32A front end MCB but we are always told to follow the manufacturers instructions and they state must be fed from a 16A supply max. No RCD needed in the 2 way unit as its already in the main consumer unit or should be.

doing it this way is so much easier than trying to mess about with 2 or 3 lots of 6mm in a cooker switch