Using pre installed cooker circuit for 13amp or 16amp oven.

[Mark armitage]

Hi all this is my first post. I am renewing my kitchen and at the moment I have a large cooker I'm changing it to a single oven. At the moment the cooker is on its own dedicated circuit with a 32mcb and 6mm cable going to a 45a cooker switch then going to a 45a cooker outlet plate which the cooker connects to with 6mm cable. I haven't decided on oven yet the two I'm looking at one says it's a 13amp and needs hardwiring and the other is a 16 amp and needs hardwiring. Could either one of them ovens just be hard wired into the cooker outlet plate that is there using the cooker circuit that is already installed and what size cable would be needed for this or would I have to change the 6mm cable to smaller cable and the mcb to a lower amp instead of 32mcb as there only either 13amp or 16amp ovens. Or could I keep the 6mm cable and 32mcb and replace cooker outlet plate with a 20amp outlet plate or 20a fuse spur for 16amp oven or a 13a fuse spur for the 13amp oven.The ratings for both ovens are
13amp oven
Requires hardwiring to a 13 Amp fuse
Power supply 13 Amp (Requires hardwiring to a fused spur)
Electrical power rating 3.3 kW
16amp oven
Electrical installation- Requires hardwiring to a 16 Amp fuse.
Power supply 16 Amp (Requires hardwiring to a dedicated circuit)
Electrical power rating.3.3 kW
I will be getting a electrician to do it just want to get a idea how it's done before get quotes
Cheers

 

[brianmoooore]

Manufacturer's instructions are manufacturer's instructions, but I would NOT be happy wiring a 3.3kW appliance through a 13A fuse. The fuse will be operating right at the edge or over its limit, and will cause heat damage to its enclosure in not too long a time.
With either oven, I'd change the MCB in the consumer unit to 16A with no other fusing.

 

[Mark armitage]

Manufacturer's instructions are manufacturer's instructions, but I would NOT be happy wiring a 3.3kW appliance through a 13A fuse. The fuse will be operating right at the edge or over its limit, and will cause heat damage to its enclosure in not too long a time.
With either oven, I'd change the MCB in the consumer unit to 16A with no other fusing.

Thanks for reply if change MCB to 16a would this mean I would have to change the 6mm cable running from the MCB to cooker switch and cooker plate or could I leave it in place will 6mm cable be ok on 16amp MCB. Also with the 16amp oven would it be best to get a 20amp MCB or would 16 be ok.cheers

 

[brianmoooore]

There's no problem with a cable that's larger than it needs to be, other than sometimes a large cable won't fit into the terminals of what it connects to, but 6mm2 will be fine. Sometimes, if a cable is long, it needs to be oversized for voltage drop reasons.
If the manufacturer states 16A fusing is OK for the larger oven, then go with a 16A MCB. MCBs don't cook their surroundings quite like a fuse dose.
Any wiring that has to be added need only be rated for 16A.

 

[Mark armitage]

There's no problem with a cable that's larger than it needs to be, other than sometimes a large cable won't fit into the terminals of what it connects to, but 6mm2 will be fine. Sometimes, if a cable is long, it needs to be oversized for voltage drop reasons.
If the manufacturer states 16A fusing is OK for the larger oven, then go with a 16A MCB. MCBs don't cook their surroundings quite like a fuse dose.
Any wiring that has to be added need only be rated for 16A.

Thanks if I chose the 13amp oven should i put a 13amp MCB in
Or for either oven would it be a case of changing MCB to 16amp one then leaving same set up(all 6mm cable and 45a cooker switch and 45a cooker plate) and just wiring oven straight into cooker outlet plate with 2.5mm flex cable.

 

[brianmoooore]

No such thing as a 13A MCB, so 16A Type B for either as your electrician will know.

 

[Darkwood]

To be honest there should be no need to de-rate the circuit at all, the item would almost certainly be classed as a fixed load appliances in that it cannot exceed it max stated current demand so overload consideration is mute here if the existing circuit is already larger.
Assuming the ELI satisfies the existing circuit then I cannot see any reason why it cannot be simply connected as is to the existing outlet, short circuit protection is covered and unless the manufacturers instructions state the exact size of the mcb as a max' rating then your good to go.

Although we often do not apply fixed circuit logic to domestic it is simply the fact most circuits in domestic are fixed load, the exception been ring mains, even lighting can be given a max fixed rating by counting the effective highest available lamp sizes and toting them up, the limiting factor though is another regulation regarding the max current rating protecting lamp-holders in lighting circuits before someone quotes that, it is often easier to just spec domestic in the usual manner at the end of the day.

 

[brianmoooore]

unless the manufacturers instructions state the exact size of the mcb as a max' rating then your good to go.

In this particular case, looking at the OP, it appears they do.

 

[Darkwood]

In this particular case, looking at the OP, it appears they do.

I see why you say that but it is ambiguous how he has posted the info, is this his own interpretation or the manufacturers guideline, also I would like to read it myself to see whether there is room for movement on this, there is a difference between spec'd manufacturers guidance saying 'at least 13/16 amp supply' and one that says 'this product requires fusing at 13/16amp'.

 

[westward10]

No such thing as a 13A MCB, so 16A Type B for either as your electrician will know.

This is not true. Memshield 2 produced 13A mcbs which I have fitted for a kitchen spec. Schneider also produced them although they are now discontinued. Wyle do a 13A combined mcb/rcbo/afdd 13A Double Pole 1 Module B Curve 6kA 30mA AFDD Combined RCBO - https://www.cef.co.uk/catalogue/products/4832498-13a-double-pole-1-module-b-curve-6ka-30ma-afdd-combined-rcbo