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

 

[Mark armitage]

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'.

Thanks I got the info of Curry's website I've attached screenshots of it.

 

[Mark armitage]

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

So if I went with 13amp oven should I ask for 13amp MCB or 16amp MCB to be fitted what would be best?

 

[brianmoooore]

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

I simplified my post for a DIYer. I'm fully aware that you can get MCBs in almost any rating you want, but the chances of the OP finding anything other than 6, 16, 20 and 32 in the range in question, available, and suitable for fitting in his CU, are negligible.
Of more concern is manufacturer's instructions for a 3.3kW @ 230volt appliance to be fed through a 13Afuse. 3.3kW @ 230v = 14.35A

 

[Dartlec]

Thanks I got the info of Curry's website I've attached screenshots of it.

Unfortunately websites are very bad at giving the useful information on ovens/hobs etc.

In this case, the manual for the hisense bsa5221abUK doesn't help either -as it says "Instructions for installation and connection are supplied on a separate sheet." which isn't available for download....

The only thing it does seem to mention is that a means for disconnection must be provided.

I personally would not consider it appropriate for a 3300W device (13.75A even at 240V ) to be put on a 13A fused spur, Many fused spurs will simply melt if run at anywhere near their full potential for any length of time. Personally I'd put that on a 20A DP switch usually from a 20A breaker if newly installing, and in this case I'd just re-use the existing wiring and connect straight to the cooker point.

It's also not clear whether either oven comes with a flex, but anything of 2.5mm flex or bigger would be likely to cope with the fault on a 32A MCB in any case.

If an electrician will be doing it anyway they could run the calcs and confirm - or just use 4mm or 6mm flex to the oven if necessary to ensure the cable is protected.

It would be interesting to contact HiSense and ask them why their two ovens, with apparently the same rating in kW, are stated as requiring different installation methods.

I wouldn't be surprised if these are 'converted' instructions from european market models, where 15A single circuits are often the most common it seems...

 

[Mark armitage]

I simplified my post for a DIYer. I'm fully aware that you can get MCBs in almost any rating you want, but the chances of the OP finding anything other than 6, 16, 20 and 32 in the range in question, available, and suitable for fitting in his CU, are negligible.
Of more concern is manufacturer's instructions for a 3.3kW @ 230volt appliance to be fed through a 13Afuse. 3.3kW @ 230v = 14.35A

So in this case I should go against the manufacturers instructions and get a 16a MCB and go straight into oven from cooker plate connection and not use 13amp fuse spur. Would this be ok if oven was supplied with 1.5mm cable considering all other cable is 6mm upto cooker plate or should I get electrician to put thicker cable if this is case

I simplified my post for a DIYer. I'm fully aware that you can get MCBs in almost any rating you want, but the chances of the OP finding anything other than 6, 16, 20 and 32 in the range in question, available, and suitable for fitting in his CU, are negligible.
Of more concern is manufacturer's instructions for a 3.3kW @ 230volt appliance to be fed through a 13Afuse. 3.3kW @ 230v = 14.35A

Thanks so on this occasion would you go against manufacturers Instructions and not use a 13amp fuse spur and just get electrician to wire cable straight into cooker outlet. If the oven cable is only thin for 13amp would that be ok considering all other cables are 6mm or would i need get electrician to put thicker cable from oven to cooker plate or would that not be advised to do that.

 

[brianmoooore]

1.5mm2 H07RN-F cable will be operating right at the limits of its specification when you take into account the ambient temperature it will operate at inside the oven's cabinet, so 2.5mm2 would be preferable.
Another problem that occurs with this imported stuff, is that they are often designed for three phase supplies, and the connecting boxes are really only designed for 1.0mm2 cables.1.5mm2 can be difficult, and 2.5mm2 close to impossible.
If this cooker runs at its stated maximum wattage for any length of time, it will destroy a fused connection unit containing a standard 13A fuse, similar to that found in 13A plugs. Very dubious instructions, that Curry's should be asked to justify.

 

[Mark armitage]

1.5mm2 H07RN-F cable will be operating right at the limits of its specification when you take into account the ambient temperature it will operate at inside the oven's cabinet, so 2.5mm2 would be preferable.
Another problem that occurs with this imported stuff, is that they are often designed for three phase supplies, and the connecting boxes are really only designed for 1.0mm2 cables.1.5mm2 can be difficult, and 2.5mm2 close to impossible.
If this cooker runs at its stated maximum wattage for any length of time, it will destroy a fused connection unit containing a standard 13A fuse, similar to that found in 13A plugs. Very dubious instructions, that Curry's should be asked to justify.

Thanks a electrician is coming to look tomorrow so just wanted check I've got this correct if the cable supplied on oven is any thinner than 2.5mm2 I should ask electrician to change it to 2.5mm2 and get them to wire straight into cooker plate and then change 32MCB for 16amp one if that correct. Will it be ok with 2.5mm2 if rest is 6mm2.?

 

[Mark armitage]

Unfortunately websites are very bad at giving the useful information on ovens/hobs etc.

In this case, the manual for the hisense bsa5221abUK doesn't help either -as it says "Instructions for installation and connection are supplied on a separate sheet." which isn't available for download....

The only thing it does seem to mention is that a means for disconnection must be provided.

I personally would not consider it appropriate for a 3300W device (13.75A even at 240V ) to be put on a 13A fused spur, Many fused spurs will simply melt if run at anywhere near their full potential for any length of time. Personally I'd put that on a 20A DP switch usually from a 20A breaker if newly installing, and in this case I'd just re-use the existing wiring and connect straight to the cooker point.

It's also not clear whether either oven comes with a flex, but anything of 2.5mm flex or bigger would be likely to cope with the fault on a 32A MCB in any case.

If an electrician will be doing it anyway they could run the calcs and confirm - or just use 4mm or 6mm flex to the oven if necessary to ensure the cable is protected.

It would be interesting to contact HiSense and ask them why their two ovens, with apparently the same rating in kW, are stated as requiring different installation methods.

I wouldn't be surprised if these are 'converted' instructions from european market models, where 15A single circuits are often the most common it seems...

I found these on hisense website what I don't understand it's states the 16amp oven needs 13amp power supply and a gas Safe engineer no idea why as it's not gas and the 13amp one doesn't need 13amp power supply.

 

[Dartlec]

I found these on hisense website what I don't understand it's states the 16amp oven needs 13amp power supply and a gas Safe engineer no idea why as it's not gas and the 13amp one doesn't need 13amp power supply.

Yes, I suspect that's just a plain error - quite common sadly - sometimes even the manual that comes with it doesn't clarify things.

I think what you said in your last post was more or less the best option. At least 2.5mm flex (some come with a flex, others don't).

The electrician can make an assessment as to whether changing the MCB to a 16A is required. That will probably depend on the length of the cable, the earthing arrangement, etc.

I assume the Cooker connection unit is less than 3m from where the oven will be? If so, then there should be no problem with going from 6mm to 2.5mm - But if MCB is changed to 16A (there may be a spare one in the board, depending on your setup, so may involve only a quick swap of one wire), then you are covered in any and all circumstances...

 

[Mark armitage]

Yes, I suspect that's just a plain error - quite common sadly - sometimes even the manual that comes with it doesn't clarify things.

I think what you said in your last post was more or less the best option. At least 2.5mm flex (some come with a flex, others don't).

The electrician can make an assessment as to whether changing the MCB to a 16A is required. That will probably depend on the length of the cable, the earthing arrangement, etc.

I assume the Cooker connection unit is less than 3m from where the oven will be? If so, then there should be no problem with going from 6mm to 2.5mm - But if MCB is changed to 16A (there may be a spare one in the board, depending on your setup, so may involve only a quick swap of one wire), then you are covered in any and all circumstances...

Yes at moment cooker connection is behind cooker but we are changing it from a freestanding to built in one so it will still be behind oven but oven will be in built in unit will this be ok or as I best asking electrician to move it to the side in one of the cupboards.

 

[brianmoooore]

Connection unit is OK behind a built in cooker, as long as there's room for it, and it's not in line with any vent the oven has.

 

[Dartlec]

Yes at moment cooker connection is behind cooker but we are changing it from a freestanding to built in one so it will still be behind oven but oven will be in built in unit will this be ok or as I best asking electrician to move it to the side in one of the cupboards.

That's fine - I assume the existing isolation switch will still be accessible?

 

[Mark armitage]

That's fine - I assume the existing isolation switch will still be accessible?

Yes the cooker switch is above the laminate worktop then it goes to cooker plate behind oven.

 

[Mark armitage]

Was just speaking with wife and she doesn't really like cooker switch on show was just thinking could we get it disconnected and put it in drawer unit next to oven instead of cooker plate so the isolation switch was out of sight or do we still need cooker plate connection as well?

 

[brianmoooore]

Very poor practice to put an isolator out of sight.

 

[Dartlec]

It's meant to be easily accessible so that it can be turned off if something happens, such as the oven catching fire or sparking - sometimes people consider putting it in a cupboard acceptable but if there is already one above the worktop I would say it should stay there. You can get nicer looking ones if that is an issue - or reduce it from a double width with socket, to a single switch.

At the very least it needs to be at the front of a cupboard clearly accessible, not where you'd have to reach around or over the oven to get to it and not behind the contents of the cupboard....

 

[Mark armitage]

Thanks for all info I have much clearer idea now. Yes it's just a white cooker switch have never like it but now we're getting it done will leave it were it is and change it for Chrome. Just got last of units out and looking now not sure if there be enough room for cooker connection plate to stay were it is once kitchen unit and oven is in place is it ok to put connection plate inside cupboard screwed to cupboard with a drywall box.

 

[Dartlec]

Thanks for all info I have much clearer idea now. Yes it's just a white cooker switch have never like it but now we're getting it done will leave it were it is and change it for Chrome. Just got last of units out and looking now not sure if there be enough room for cooker connection plate to stay were it is once kitchen unit and oven is in place is it ok to put connection plate inside cupboard screwed to cupboard with a drywall box.

As long as the back of the cupboard is strong enough to hold it and not the thin plywood, that's fine - it doesn't need to be accessed once the cover is back on until the next inspection or change of oven. Only issue may be routing of cables, but electrician tomorrow should be able to work out the easiest way to do it and still keep things correct...

 

[Mark armitage]

Thanks electrician came out said was ok to keep everything how it is. Just got to wait for oven to be delivered to see what cable oven is supplied with to determine weather it be best to change mcb from 32mcb to 16mcb. Said if it was thinner cable be best to change mcb.I asked about changing 45a cooker switch to 20a as was smaller oven he said no need as 45a is its maximum it will work at lower. Does that sound about right?

 

[Dartlec]

Thanks electrician came out said was ok to keep everything how it is. Just got to wait for oven to be delivered to see what cable oven is supplied with to determine weather it be best to change mcb from 32mcb to 16mcb. Said if it was thinner cable be best to change mcb.I asked about changing 45a cooker switch to 20a as was smaller oven he said no need as 45a is its maximum it will work at lower. Does that sound about right?

That all sounds fine - the rating of the switch is purely the maximum current it can take so there is no benefit in reducing it. The existing 6mm cable might well be a struggle in most 20A switches anyway..

 

[Mark armitage]

Hi again so oven came today it's has a flex cable on it. It's stamped H05VV-F 3G 1.5. so guessing it's a 1.5mm cable. will a 1.5mm cable be ok to be connected to connection plate that is in wall and just changed MCB to 16amp or would I need get electrician to change cable to 2.5mm as well. Cheers

 

[brianmoooore]

If the oven is supplied with 1.5mm2 cable, then that is fine. If it came without cable, and I was installing it, I'd fit 2.5mm2 by preference, if I thought the terminals would accept it.

 

[Mark armitage]

If the oven is supplied with 1.5mm2 cable, then that is fine. If it came without cable, and I was installing it, I'd fit 2.5mm2 by preference, if I thought the terminals would accept it.

Thanks I did look at 1.5mm amp ratings and some said has rating of 15amp is that true? Would it be better to fit 13amp fuse spur switch to protect cooker cable or not?

 

[brianmoooore]

1.5mm2 cable is within its rating at room temp., but it's likely to be a bit warmer than that behind an oven in an enclosure.
The cable does NOT need protecting against overload, only against short circuit, which the MCB in the CU will do.
Do not run this oven through a 13A fuse for the reasons mentioned earlier in the thread.

 

[Mark armitage]

Thanks for all your help just wanted double check the 1.5mm would still be in 16amp rating were it's warmer behind the oven in a enclosure then?as only installation instructions I could find were from Curry's and of hisense website and they both said hard wire to 13amp fuse spur. Which seems strange for reasons mentioned here. There were no installation instructions with oven only that it was 3.3kw.