Reading the On-site Guide: Given that a 32A domestic cooker supply is 'good' for 15kW cooking appliance and that the load of cooking appliances is 10A + 30% f.l. in excess of 10A, does this mean that a 13A socket can be used for a 20A oven? 
cooking appliance diversity
- Thread starter ajrobb
- Start date
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lol Nice1 AJ,
I imagine you'd be hard pushed to find a reg that explicity prohibits it, but it just seems so wrong to do it.
Don't forget that when you use a plug and socket, you have introduced an new protective device and that the cooker has now got a 13A element there, not just a 32A element.
I imagine you'd be hard pushed to find a reg that explicity prohibits it, but it just seems so wrong to do it.
Don't forget that when you use a plug and socket, you have introduced an new protective device and that the cooker has now got a 13A element there, not just a 32A element.
I'm not sure I'd trust a plug and socket, but a 13A FCU with a 20A isolator... As long as the main circuit protection is not more than 32A (for the FCU). This could make it easy to use a 32A circuit for most oven and hob combinations.
Example: most Hotpoint single ovens require max 16A protection for their 1.5mm² internal wiring (but a 13A socket is given as an option in MI)
It just seems WRONG
Example: most Hotpoint single ovens require max 16A protection for their 1.5mm² internal wiring (but a 13A socket is given as an option in MI)
It just seems WRONG
It depends what is meant by a 20A oven. If it's a single oven that draws 20A when the heating element is on, then there's no diversity. At the other end of the spectrum, if it was an appliance with 4 little ovens, diversity could be applied on the assumption that not all the elements would be on at the same time.
But if it's a double oven, rated at say 5kW, then we could attempt to claim diversity, but since using both 2 ovens at once is more likely than using 4, I suspect that a supply of spare fuses would be in order - demonstrating that the load is not diverse enough!
(PS Can you tell I'm a bit bored?)
But if it's a double oven, rated at say 5kW, then we could attempt to claim diversity, but since using both 2 ovens at once is more likely than using 4, I suspect that a supply of spare fuses would be in order - demonstrating that the load is not diverse enough!
(PS Can you tell I'm a bit bored?)
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Many continental ovens and double ovens have a full load current of about 16A. This is annoying for UK consumers (but music to the wallets of sparks) who get an extra 20A supply run to the kitchen for the oven.
From http://www.prioryconsultants.co.uk/cartridge_fuses.htm
"A BS 1362 cartridge fuse must therefore be able to carry a current of 1.6 In for 30 minutes without melting but operate within 30 minutes when carrying a current of 1.9 In."
1.6 * 13A is 20.8A for 30 minutes
I suspect that diversity comes from the duty cycle as well as the number of elements.
From http://www.prioryconsultants.co.uk/cartridge_fuses.htm
"A BS 1362 cartridge fuse must therefore be able to carry a current of 1.6 In for 30 minutes without melting but operate within 30 minutes when carrying a current of 1.9 In."
1.6 * 13A is 20.8A for 30 minutes
I suspect that diversity comes from the duty cycle as well as the number of elements.
I do take your point that a lot of these instructions just assume that it will be connected to a 16A continental circuit.
If you legitimately demonstrate, using sound principles, that the appliance load is diverse enough that it would not overload a 13A accessory, or more easily that the actual load of the oven is less than 13A, then you could have a sound argument against the MI.
I do think however that extending the diversity principles based around 1 oven + grill + 4 hob rings to just 2 ovens is not sound.
If you legitimately demonstrate, using sound principles, that the appliance load is diverse enough that it would not overload a 13A accessory, or more easily that the actual load of the oven is less than 13A, then you could have a sound argument against the MI.
I do think however that extending the diversity principles based around 1 oven + grill + 4 hob rings to just 2 ovens is not sound.
It is quite common to start cooking all at once (all rings, ovens and kettle turned straight to max). Modern rings turn themselves down fairly quickly and more powerful ovens heat up quickly, so a poor 32A circuit can be called on to provide 18kW for short periods (15kW cooker plus 3kW kettle in the socket). That is using the On-site Guide. Mind you, I wouldn't be surprised if the 32A CB tripped pretty quickly when asked to deliver 75A!
Hi AJ,
I would disagree with that. In the event of preparing a meal which would call for all of the elements to be in use, i would imagine that the start times for various bits would differ.
The oven might have been on for an hour before anyone touched a hob.
Spuds to be mashed take longer to do than warming up a pan of peas or carrots.
I think the simultaneous switch on you describe is probably very unlikely in a domestic setting.
Still wouldn't put the oven on a plug anyway
I would disagree with that. In the event of preparing a meal which would call for all of the elements to be in use, i would imagine that the start times for various bits would differ.
The oven might have been on for an hour before anyone touched a hob.
Spuds to be mashed take longer to do than warming up a pan of peas or carrots.
I think the simultaneous switch on you describe is probably very unlikely in a domestic setting.
Still wouldn't put the oven on a plug anyway
I started this topic because I was astounded that a 32A circuit could be used for a 18 kW (75A) mix of cooking appliances. Using the On-site Guide formula, it would APPEAR that a 13A cartridge fuse would be adequate for 20A of cooking appliances.
Has anybody got away with being close to the cooking appliance load indicated by the OSG?
Has anybody got away with being close to the cooking appliance load indicated by the OSG?
Err.....
Ban - those 2 quotes are clearly from 2 different contexts.
In the first I point out that diversity is not approprite for loads which do not exhibit a diverse load arrangement; comparing an oven to a complete cooker.
In the second, I agreed with AJ on the separate point that duty cycle is a factor when determining how 'diverse' loads are.
In the first I point out that diversity is not approprite for loads which do not exhibit a diverse load arrangement; comparing an oven to a complete cooker.
In the second, I agreed with AJ on the separate point that duty cycle is a factor when determining how 'diverse' loads are.
Manufacturers don't make it easy to plan or re-use an electrical installation! They mostly seem to refer to the physical plate on the actual oven. This is so frustrating as you have to buy the oven and hob first and then design a new kitchen and wiring installation to go around them.
Some ovens give a hint that they can be connected to a shared outlet. One Hotpoint double-oven installation manual even shows splitting a 6mm² feed to the connection plate to two 4mm² cables to the hob and oven. This seems dangerous as the 4mm² cables are not sufficiently protected by a 40A CB (OK with a 32A CB though).
I am planning a small galley kitchen with electric hob and built-under single oven. I shall allow for a 32A supply to a 45A cooker point with the switched supply feeding the hob and an FCU for the oven (e.g. 2.3kW Hotpoint SN56EX). The 1.5mm² oven wiring mandates a maximum fuse of 16A.
The OSG seems to imply that ALL domestic cooking appliances should be supplied from a single 32A supply unless they total more than 15 kW. Only then should larger or dedicated supplies be considered. By having a 32A CB, the kettle socket is also reasonably protected.
I take the point that diversity ought not to be applied to a single component. Thus, if the largest component (oven or grill) draws a current greater than 10A, then the diversity calculation should be current of the largest component plus 30% of the full-load current in excess of this largest component. However, if the largest component draws less than 10A, then the OSG formula should apply.
The 2.3kW oven above draws 10A, so a single 13A supply could be used for two 2.3kW ovens. Oh, and because I have a fused spur, I could plug both ovens into one double-gang socket!
It is not clear, maybe the diversity calculation should be only used when cooking appliances total more than 15 kW?
Some ovens give a hint that they can be connected to a shared outlet. One Hotpoint double-oven installation manual even shows splitting a 6mm² feed to the connection plate to two 4mm² cables to the hob and oven. This seems dangerous as the 4mm² cables are not sufficiently protected by a 40A CB (OK with a 32A CB though).
I am planning a small galley kitchen with electric hob and built-under single oven. I shall allow for a 32A supply to a 45A cooker point with the switched supply feeding the hob and an FCU for the oven (e.g. 2.3kW Hotpoint SN56EX). The 1.5mm² oven wiring mandates a maximum fuse of 16A.
The OSG seems to imply that ALL domestic cooking appliances should be supplied from a single 32A supply unless they total more than 15 kW. Only then should larger or dedicated supplies be considered. By having a 32A CB, the kettle socket is also reasonably protected.
I take the point that diversity ought not to be applied to a single component. Thus, if the largest component (oven or grill) draws a current greater than 10A, then the diversity calculation should be current of the largest component plus 30% of the full-load current in excess of this largest component. However, if the largest component draws less than 10A, then the OSG formula should apply.
The 2.3kW oven above draws 10A, so a single 13A supply could be used for two 2.3kW ovens.
Oh, and because I have a fused spur, I could plug both ovens into one double-gang socket!It is not clear, maybe the diversity calculation should be only used when cooking appliances total more than 15 kW?
From OSG: A circuit of rating exceeding 15A but less than 50A may be used to supply two or more cooking appliances in the same room.
The 32A circuit for up to 15kW is described as 'usually appropriate' and is a result of applying the diversity formula for cooking appliances.
This arrangment with a dual outlet, or 2 outlets, to which you could alternately fit FCUs if necessary covers most eventualities.
The 32A circuit for up to 15kW is described as 'usually appropriate' and is a result of applying the diversity formula for cooking appliances.
This arrangment with a dual outlet, or 2 outlets, to which you could alternately fit FCUs if necessary covers most eventualities.
Thanks, found it "8.4 Cooker circuits in household and similar premises" para 3
Phew, so 13A FCU (fused spur) is specifically excluded from supplying two cooking appliances as it doesn't exceed 15A.
I can see that 32A minus 5A for socket outlet leaves 27A. Diversity says combined full load is 10A + (27A - 10A)/0.3 = 66.7A or 15.3kW (close to 15kW figure in OSG). I'm a little concerned that OSG says "30 or 32 A".
A 16A supply can therefore be used for a total of 10A + (16A - 10A)/0.3 = 30A or 6.9kW of cooking appliances - enough for most hobs.
I accept that whatever the OSG/BR says is the worst acceptable case. Supplying each appliance with a supply capable of sustained full-load current is going to avoid possibility of CBs tripping.
Phew, so 13A FCU (fused spur) is specifically excluded from supplying two cooking appliances as it doesn't exceed 15A.
I can see that 32A minus 5A for socket outlet leaves 27A. Diversity says combined full load is 10A + (27A - 10A)/0.3 = 66.7A or 15.3kW (close to 15kW figure in OSG). I'm a little concerned that OSG says "30 or 32 A".
A 16A supply can therefore be used for a total of 10A + (16A - 10A)/0.3 = 30A or 6.9kW of cooking appliances - enough for most hobs.
I accept that whatever the OSG/BR says is the worst acceptable case. Supplying each appliance with a supply capable of sustained full-load current is going to avoid possibility of CBs tripping.
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