Hob and oven single supply cable

[eggandspoon]

Hi

I know this has been done to death, but was looking for some definitive opinions.

Eg 6mm t+e 4kw double oven 7kw hob 32a MCB or 40a MCB

From searching the forum it appears acceptable to connect both appliances to a single supply bearing in mind diversity.

It has been stated that 2.5 hr flex for oven and 4mm for hob connected to outlet plate.

The 32a MCB would not protect the 2.5 for overload (unlikely) but would for short circuit.


If the manufacturer has no requirement for MCB sizing is the above acceptable? I.e. were protecting the external cable not the load.

However if the manufacturer states 20a ocpd would it be necessary to add a cu to split cable and provide this.

I've seen it done both ways , a recent kitchen install 20a double oven 45 a dp switch, 6 mm cable 40a MCB.


A lot of appliances Bosch Siemens neff now supplying combined ovens, micros etc as 16 a how does everyone supply these especially a a retro fit.

Sorry for rambling post hope you can extract what I'm asking.

 

[Midwest]

You should start with what the manufacturer recommends in terms of electrical connections for each appliances. The oven comes supplied with 2.5mm flex?

 

[Darkwood]

This is usually a question that still splits the forum, I sit in the park of suitable wiring for max demand without diversity.

Diversity in domestic is for total KVA demand on the supply not for final circuit design, if you are able to switch on all oven and hob loads on together then your cable should be suited to that possibility.

You could wire in say 10mm 'calcs' permitting and use a dual cooker outlet thus acheiving the 1 circuit design, the oven and hob can be classed as fixed loads as long as you circuit can handle both max plated loads together thus only requiring S/C protection for the reduced flexes to the hob and oven.

 

[Midwest]

Think you would be pushing the limits for protecting a 6mm tw&e with 40amp mcb, unless it was clipped direct etc. What are your calculations for total loads for each appliance, after applying diversity, or does the manufacture state max load for each appliance? (appreciate they often state total max load, as opposed actual max load)

 

[Midwest]

Some manufacturers will state total max load, their appliance can draw at any one time, e.g. ovens can generally only have fan oven or top & bottom grill on at anyone time. Hobs can physically have all four hobs on at once, but someone here will be able to explain thermostats switching etc. I never known a standard separate oven/hob set up need more than 6mm & 32amp MCB or cause it to trip.

 

[DuaneMHunt1976]

think 10mm Cable looking at 45A what is about 10KW and your MAX is 11KW

as someone said 6mm you would have to have it CLIPPED to WALL for it be able to handle 45A
so 6mm would be around 32A range, IV, looking 7KW range

 

[Octopus]

think 10mm Cable looking at 45A what is about 10KW and your MAX is 11KW

as someone said 6mm you would have to have it CLIPPED to WALL for it be able to handle 45A
so 6mm would be around 32A range, IV, looking 7KW range

hum......

Our cooker has a "theoretical" combined load of 17.7kw - yet the manufacturers state the cable minimum to be 6mm T&E!

 

[davesparks]

This is usually a question that still splits the forum, I sit in the park of suitable wiring for max demand without diversity.

For a domestic cooking load? This has been tried and tested over and over again, the diversity calculations work for the final circuit design in this case.

Even the 'what if they're cooking chris as dinner' line which gets rolled out every time is nonsense. There's no way every element will be switched on at the same time, you don't start cooking the turkey at the same time as the vegetables!

 

[DuaneMHunt1976]

hum......

Our cooker has a "theoretical" combined load of 17.7kw - yet the manufacturers state the cable minimum to be 6mm T&E!

I was looking at the Current Carrying Capacity Tables 6mm Clip to wall it says 46A, as you know 230v x 46A = 10580W
not taking in to account any voltage drop.

 

[Darkwood]

hum......

Our cooker has a "theoretical" combined load of 17.7kw - yet the manufacturers state the cable minimum to be 6mm T&E!

Can this ever happen though - some designs limit the actual loads that can be on together with selection switches etc, I cannot understand the manufacturers stating cable size either as they cannot know the installation methods although you do say minimum... even taking into account rheostat control if its completely possible that you can have most of the loads on then the cable must be protected however rare these occasions are - you may choose to do this with the front end device but I'd rather not be called out on xmas day because the whole family is arround and the oven/hob are in high demand.


Yep the xmas dinner line ... ps I'll admit it isn't often but I live in a clicky small town and everyone knows everyone, I have been contacted twice on xmas day for this very reason albeit twice over 20yrs -it does occur.

 

[Midwest]

Think most domestic ovens have relatively small elements, my range style oven has a manufactures 1.5mm flex. Takes an age to cook the roasties! Hobs do have larger elements and I've seen all four rings in use. But I'm led to believe that due to thermostat switching (waiting for someone to explain that again), there'll be little time when all four will be on at one time, even when selected on high.

 

[Octopus]

Can this ever happen though - some designs limit the actual loads that can be on together with selection switches etc, I cannot understand the manufacturers stating cable size either as they cannot know the installation methods although you do say minimum... even taking into account rheostat control if its completely possible that you can have most of the loads on then the cable must be protected however rare these occasions are - you may choose to do this with the front end device but I'd rather not be called out on xmas day because the whole family is arround and the oven/hob are in high demand.


Yep the xmas dinner line ... ps I'll admit it isn't often but I live in a clicky small town and everyone knows everyone, I have been contacted twice on xmas day for this very reason albeit twice over 20yrs -it does occur.

Not tried it but yes is what I think!

2 ovens, separate grill and 5 "rings" on the induction grill - so yes, possible to turn them all on together........

 

[Midwest]

Not tried it but yes is what I think!

2 ovens, separate grill and 5 "rings" on the induction grill - so yes, possible to turn them all on together........

Can I cook my roast at your house!

 

[telectrix]

For a domestic cooking load? This has been tried and tested over and over again, the diversity calculations work for the final circuit design in this case.

Even the 'what if they're cooking chris as dinner' line which gets rolled out every time is nonsense. There's no way every element will be switched on at the same time, you don't start cooking the turkey at the same time as the vegetables!

what has the wife's sister and mother got to do with it?

 

[Darkwood]

There is the argument here though that when domestic cookers/ranges hobs get to silly sizes then of course you can reliably say if not used as a commercial venture then you can apply a comfortable diversity without worry .. possibly in murdochs case with a 17+ KW cooker and as long as the cable is protected from overload then yes I may be nudged to agree - but in the OP's case where these are standard ratings and the probability of utilising max demand then I would be designing the circuit to this possibility.

 

[amlu]

fuse it down to whatever that 6mm cable can safely carry, inform the customers that it "may" trip when overloaded, and if it does and they not happy with it then is a bigger job to upgrade the circuit...

 

[Octopus]

Because we were refurbishing the house completely, I ran 10mm T&E from the board to the isolator!

 

[eggandspoon]

Thanks for all the input - on reading this thread and other forums I,ve come to some conclusions please correct me if I'm wrong

2 appliance can come from 1 supply - as long as within 2 m of isolator and diversity and cable factors allow it ?

If the manufacturer states a OCPD of x this should be done and therefore may require a separate supply or split with a local cu - but if not done it should be OK ?

If oven say 3kw comes with flex and a plugtop fitted - fit socket or spur to supply ?

If oven does not come with flex and/or plugtop say 3kw can be connected direct to supply ? Using appropriate flex say 1.5mm

Overriding factor is that cooking appliances are fixed loads and do not need ocp the MCB should be matched to the supply cable which will provide short circuit protection. ?

Diversity and the fact that loads cycle on and off should ensure that a B MCB would not trip even at full load for a short while ?


Please add your comments:smiley2:

 

[Midwest]

Can't do that multi quote thing, so; 1) Yes. 2) Amendment 3 says we should 'take account of manufacturers instructions', but you are designing the circuit for the load. 3) Never come across a 3kw appliance with a fitted plug top? 4) Appendix 15 (I think its 15) suggests appliances above 2kw, should be on their own radial circuit. 5) Not sure what you saying here? 6) Yes in essence.

 

[eggandspoon]

Can't do that multi quote thing, so; 1) Yes. 2) Amendment 3 says we should 'take account of manufacturers instructions', but you are designing the circuit for the load. 3) Never come across a 3kw appliance with a fitted plug top? 4) Appendix 15 (I think its 15) suggests appliances above 2kw, should be on their own radial circuit. 5) Not sure what you saying here? 6) Yes in essence.

Hi thanks for taking the time to reply.

3) some ovens ive have a pretty fitted moulded plug, some have flax some don't



4) seems to cancel out 2 appliances on same circuit !

5) cooking appliance are fixed loads and therefore should not be capable of overloading the correctly sized cable attached to them that matches the load The circuit MCB does not have to be designed to match the appliance cable - only the supply cable and will !provide overload protection for supply cable and short circuit protection for entire circuit.


Ultimately I was trying to get some definitive answers for most situations.

 

[Midwest]

3) I've never come across an 3kw appliance with a BS1363 plug, but if you have then I'm prepared to be convinced. And some ovens come with a connecting cable, some don't (mostly those requiring 4mm& above).
4) Appendix 15 refers to connecting 2kw appliances to ring final circuits (page 453 BYB). You can connect more than one appliance to one circuit, so long as it is designed correctly.
5) Yes

 

[davesparks]

3) I've never come across an 3kw appliance with a BS1363 plug, but if you have then I'm prepared to be convinced.

Not sure if they still do them but screwfix used to sell a 3kW Stanley industrial looking fan heater with a moulded 13A plug on it.
I've replaced a few sockets for a customer who bought a job lot of them.

 

[Midwest]

Blimey, plug a few of those into your ring will get the cables humming!

 

[davesparks]

Yes it did!
With everything else they had in the building they got L1 up to ~125A on a 100A service (L2 ~40A, L3 ~20A)