32A to 63A

[OldKettle]

Hi,
I have a Wylex NHRS6604 board which has a dedicated 32A cooker circuit, with a 20A double oven running on it.

I want to have an induction hob installed, which is 32A (7.4Kw). There are two circuits for the sockets in the house, which are both 32A.

There are two unused slots on the board, so I will probably have to get an electrician to install a new circuit for the induction hob in one of those slots.

I did wonder, though, whether it would be possible get them to, instead, just up the rating of the oven circuit, to accommodate hob and the oven (total of 52A). I noticed that you can get breakers that go up to 63A.

The existing cabling is 6mm, contained in conduit, in the wall for about 2 metres. I think that would be OK for 52A but not the full 63A.

Is it possible to upgrade the circuit to 63A and would that require them to upgrade the cabling? (if it needs upgrading, then a new circuit is probably just easier)

 

[Adam_151]

Most domestic consumer units don't have a 63A breaker available for them, some makes might, especially if the manufacturer also produces other distribution baords other than consumer units... this is moot though, because you wouldn't fit a 63A to 6mm cable, nor would you need to feed a domstic cooker on a 63A breaker!

Cooking appliance diversity is 10A of the total load, plus 30% of the rest, plus 5A if theres a socket on the cooker switch

Even assuming your oven is the full 20A (its more likely to be ~16A ish) that gives just shy of 23A without socket, and just under 28A with. With traditional diversity rules a 32A circuit for both would be fine, induction hobs do represent a little bit of a diffeernt load profile to traditional hobs though as they can route more of the available power to the rings in use if you put them in fast boil mode, etc. If one wanted to engineer on the side of caution a 40A circuit could used for both, but there is no way that it would need to be any bigger than this, ever!

 

[10monty]

Most domestic consumer units don't have a 63A breaker available for them, some makes might, especially if the manufacturer also produces other distribution baords other than consumer units... this is moot though, because you wouldn't fit a 63A to 6mm cable, nor would you need to feed a domstic cooker on a 63A breaker!

Cooking appliance diversity is 10A of the total load, plus 30% of the rest, plus 5A if theres a socket on the cooker switch

Even assuming your oven is the full 20A (its more likely to be ~16A ish) that gives just shy of 23A without socket, and just under 28A with. With traditional diversity rules a 32A circuit for both would be fine, induction hobs do represent a little bit of a diffeernt load profile to traditional hobs though as they can route more of the available power to the rings in use if you put them in fast boil mode, etc. If one wanted to engineer on the side of caution a 40A circuit could used for both, but there is no way that it would need to be any bigger than this, ever!

Sorry to jump on this thread but I will shortly be in a similar situation.
Is that a 32a or 40a mcb combined or one for each appliance?

 

[AndyPRK]

one of these will allow conenction of 2 cookers to a cooker circuit.

https://www.ebay.co.uk/itm/45-amp-4...405347&hash=item287bd325d2:g:ZEgAAOSwJkJWk~Np

I doubt you will have any problems on a 32A MCB. Give it a go.


If you don't already have a square outlet sunk into the wall, you should go for this one

https://www.ebay.co.uk/itm/Dual-Coo...776196?hash=item287bfb9184:g:C~cAAOSwBPxck2M8

 

[EFLImpudence]

Combined.

An oven and a hob is the same as a cooker.

A 32A circuit is good for 15kW of domestic cooking appliances; possibly more.

 

[10monty]

That's good to know. Thank you.

 

[OldKettle]

Combined.

An oven and a hob is the same as a cooker.

A 32A circuit is good for 15kW of domestic cooking appliances; possibly more.

This is excellent news.

The oven is rated at 4.9kW and the hob 7.4kW, so I will just add the hob to the same circuit.

The existing cooker switch has a 13A socket included.

Presumably that socket can still be used, because even with, say, a 3kW kettle (which is the most power hungry appliance we have), it would only peak at 15.3kW.

one of these will allow conenction of 2 cookers to a cooker circuit.

https://www.ebay.co.uk/itm/45-amp-4...405347&hash=item287bd325d2:g:ZEgAAOSwJkJWk~Np

I doubt you will have any problems on a 32A MCB. Give it a go.

Thank you. Unfortunately the oven and hob will be in different locations, separated by a door way, so I will have to wire them separately, so will probably have to upgrade the existing junction box in the ceiling.

 

[AndyPRK]

Lol. You may want to consider if it’s easier to run back to the cu as per your first post lol

 

[JohnW2]

Lol. You may want to consider if it’s easier to run back to the cu as per your first post lol

Even if that were done (for 'wiring convenience') the two (oven and hob cables) could still be fed from the same 32A MCB in the CU.

Kind Regards, John

 

[AndyPRK]

yes they could.

Though when a new CU is fitted they could be separated.

I did hear a regulation that there should be 1 circuit per MCB. Which makes sense if you have room in the cu

 

[JohnW2]

yes they could. Though when a new CU is fitted they could be separated.

They could, but I don't think there would be any real point, if a single 32A circuit was adequate.

I did hear a regulation that there should be 1 circuit per MCB. Which makes sense if you have room in the cu

I think you will find that, per BS7671 definitions, that is inevitable - since having a common OPD (MCB or fuse) is what defines 'a circuit'.

In any event, a radial which has two branches, both originating at the CU/MCB (which is what we would be talking about) is still just 'one circuit', not two.

Kind Regards, John

 

[AndyPRK]

regulation 3.1.4 was what I want thinking of

out of interest, do you have the wording?

 

[JohnW2]

regulation 3.1.4 was what I want thinking of

I presume that you mean 314.1 ...

out of interest, do you have the wording?

....

314.1 Every installation shall be divided into circuits, as necessary, to:
(i) avoid danger and minimize inconvenience in the event of a fault
(ii) facilitate safe inspection, testing and maintenance (see also Chapter 46 and Section 537)
(iii) take account of hazards that may arise from the failure of a single circuit such as a lighting circuit
(iv) reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor (PE) currents not
due to a fault
(v) mitigate the effects of electromagnetic disturbances (see also Chapter 44)
(vi) prevent the indirect energizing of a circuit intended to be isolated.

However, (a) that's different from your suggestion that "there should only be 1 circuit per MCB" (which, as I said, is inevitable per BS7671 definition) and (b) I think you would have to stretch things quite a bit to argue that 314.1 requires an oven and hob to be on different circuits (i.e. protected by different MCBs).

Kind Regards, John

 

[securespark]

Yes there is. Even in the 14th Ed (1966) there was mention of this:

A25. Note 2. In the interests of good planning, it is undesirable that the whole of the fixed lighting of an installation should be supplied from one final sub-circuit.

Then in subsequent 15th (314-1), 16th (314-01-01) & 17th Eds (314.1), something like: Every installation shall be divided into circuits as necessary to avoid danger in the event of a fault.

See red bit.
Although I don't have a copy of the 18th yet.

EDIT: Ooops. Too late.

 

[JohnW2]

See red bit. Although I don't have a copy of the 18th yet. ... Ooops. Too late.

Yes, as you've seen, it is much the same (in fact, I think identical to 17th) in 18th.

However, as I've said, although interpretations of that obviously vary appreciably, I don't think that many people would argue that it requires ovens and hobs had to be on different circuits. If it did, I doubt that there would be all that many installations out there which would conform with that requirement!

Kind Regards, John