This is a spin-off from this thread . In relation to this spin-off topic, please respond in this thread and not the original.
It is also a very long message, about the 'spirit' of diversity guidance, so many might wish to ignore it!
'The regulations', per se, obviously don't help us at all, the only available guidance about diversity being that in the OSG (mine is still red, so apologies if Table numbers etc. have changed) - which is where we find the familiar "first 10A + 30% of the rest, plus 5A if there is a socket". In my red OSG, Table 1B, which relates to diversity when used to determine the current demand of a whole installation indicates that this diversity calculation should be applied to 'connected cooking appliances', which I take to mean 'all cooking appliances in the installation’. However, Table 1A, which relates to diversity when used to determine the current demand of a final circuit, gives that same diversity calculation, but for "household cooking appliance" (singular).
In the lack of any specific guidance from the OSG, what I’m talking about is the intention/’sprit’ of the meaning of ‘a household cooking appliance’ in this context. It’s obviously a bit difficult, because, as you have implied, a domestic ‘cooking facility’ can consist of anything from just one oven (with a gas hob) to a double oven plus a hob – with the components separate or combined. My (‘common sense’?) view of the spirit is that any such ‘cooking facility’ can reasonably be treated as ‘an appliance’, the totality of which (even if ‘separates’) can be a subjected to a standard diversity calculation.
However, if there is more than one such ‘facility’ (e.g. two oven+hob combinations, one on each side of the room), I’m not sure it’s in the spirit of things to apply diversity across the two (i.e. treat them as if they were one) – not the least because it is then quite possible that two people would use the two facilities simultaneously and independently. There’s obviously a big difference ... the first 6kW ‘cooker’ would have an after-diversity current demand of 14.8A, but the second (if lumped together with the first) only 7.8A. ... or, looked at in another way, the assessed demand of each would reduce (from 14.8A) to 11.3A if diversity were applied across the two.
I know it’s atypical, but my house has more than one kitchen. If I had 6kW cookers in two of them, and decided to supply them from the same circuit, do you think it would be reasonable to protect that circuit (and size the cable) with a 25A OPD, on the basis that diversity applied across the two of them would result in a current demand of only 22.6A, or would you apply diversity separately to the two (14.8A each, hence 29.6A total) and therefore use a 32A circuit? I personally don’t feel that the former approach is within the spirit of diversity, but you quite probably do. Indeed, as you’ve pointed out, if I applied diversity across all of them, I could theoretically have three 6kW cookers in different locations in the house and still supply them from a single 32A circuit (after-combined-diversity demand ~30.4A), even though, if subjected to diversity calculations separately, they would represent a total demand of 44.4A. What do you think?
When the second ‘facility’ is a combi-microwave, the situation is even less certain in my mind - although, as I implied, my inclination (in terms of my feeling about the spirit) is that it perhaps ought to be considered as a separate appliance (and therefore not lumped with the rest for diversity calcs) – my feeling being that the microwave is more likely to be used ‘independently’ from the rest of the facilities. If one had a 6kW cooker and a 3kW combi-microwave on separate circuits, there’s no doubt that the circuits concerned would have to be designed to be able to supply at least 14.8A and 10.9A respectively – a total minimum current requirement of 25.7A. If, without physically moving any of the appliances, one then moved them onto the same circuit, and regarded them as ‘one appliance’ for the purpose of diversity, the circuit would then only have to be able to supply 18.7A.
Although I understand the statistical basis, I’m not convinced that it is ‘reasonable’ (‘within the spirit of diversity’) to say that the group of appliances require (‘on average’) 7A less when connected to the same circuit than when supplied separately. That would require (statistically) that “7A’s worth” of highs and lows of the microwave demand would cancel with those of the rest of the cooking appliances – perhaps unlikely given that even the maximum load of the microwave is only 13A. Before you say it, I realise that one could use the same argument across the hob and (maybe two) oven(s) of a cooker, but it feels to me far more in the spirit of diversity to regard them (together) as ‘a single appliance’ (to which diversity can be applied) than it does if there are two separate ‘cookers’, or ‘a cooker’ and a combi-microwave.
I suppose one way of looking at what I’m saying about the ‘spirit’ is that the further one moves from having a single ‘cooker’ (be it a single product or a combination of ‘singles’), the more one moves in the direction of the non-residential category of the OSG, where diversity calculations become much less generous (100%+80%+60% of rest) – on that basis, a 6kW cooker plus a 3kW combi-microwave would have an after-diversity current demand of 36.4A, not the 22.6A in a residential environment, and three 6kW cookers would have an after-diversity demand of 62.4A, not 30.4A.
I imagine that you are going to disagree with most of the above and say that we should just ‘blindly’ follow the OSG guidance as regards diversity (despite its lack of ‘explanatory detail’), without any consideration for the actual situation and/or our personal perception of the ‘spirit’ of diversity – but I will nevertheless be interested to hear your view.
Kind Regards, John
It is also a very long message, about the 'spirit' of diversity guidance, so many might wish to ignore it!
No, I am not asking you to 'quote and calculate per the regulations'. However, I do have 'reservations', in the sense of interpreting (particularly ‘the spirit of’) the limited available guidance on how we are meant to apply diversity to multiple cooking appliances, and was hoping for some views/insights from you about this.
'The regulations', per se, obviously don't help us at all, the only available guidance about diversity being that in the OSG (mine is still red, so apologies if Table numbers etc. have changed) - which is where we find the familiar "first 10A + 30% of the rest, plus 5A if there is a socket". In my red OSG, Table 1B, which relates to diversity when used to determine the current demand of a whole installation indicates that this diversity calculation should be applied to 'connected cooking appliances', which I take to mean 'all cooking appliances in the installation’. However, Table 1A, which relates to diversity when used to determine the current demand of a final circuit, gives that same diversity calculation, but for "household cooking appliance" (singular).
In the lack of any specific guidance from the OSG, what I’m talking about is the intention/’sprit’ of the meaning of ‘a household cooking appliance’ in this context. It’s obviously a bit difficult, because, as you have implied, a domestic ‘cooking facility’ can consist of anything from just one oven (with a gas hob) to a double oven plus a hob – with the components separate or combined. My (‘common sense’?) view of the spirit is that any such ‘cooking facility’ can reasonably be treated as ‘an appliance’, the totality of which (even if ‘separates’) can be a subjected to a standard diversity calculation.
However, if there is more than one such ‘facility’ (e.g. two oven+hob combinations, one on each side of the room), I’m not sure it’s in the spirit of things to apply diversity across the two (i.e. treat them as if they were one) – not the least because it is then quite possible that two people would use the two facilities simultaneously and independently. There’s obviously a big difference ... the first 6kW ‘cooker’ would have an after-diversity current demand of 14.8A, but the second (if lumped together with the first) only 7.8A. ... or, looked at in another way, the assessed demand of each would reduce (from 14.8A) to 11.3A if diversity were applied across the two.
I know it’s atypical, but my house has more than one kitchen. If I had 6kW cookers in two of them, and decided to supply them from the same circuit, do you think it would be reasonable to protect that circuit (and size the cable) with a 25A OPD, on the basis that diversity applied across the two of them would result in a current demand of only 22.6A, or would you apply diversity separately to the two (14.8A each, hence 29.6A total) and therefore use a 32A circuit? I personally don’t feel that the former approach is within the spirit of diversity, but you quite probably do. Indeed, as you’ve pointed out, if I applied diversity across all of them, I could theoretically have three 6kW cookers in different locations in the house and still supply them from a single 32A circuit (after-combined-diversity demand ~30.4A), even though, if subjected to diversity calculations separately, they would represent a total demand of 44.4A. What do you think?
When the second ‘facility’ is a combi-microwave, the situation is even less certain in my mind - although, as I implied, my inclination (in terms of my feeling about the spirit) is that it perhaps ought to be considered as a separate appliance (and therefore not lumped with the rest for diversity calcs) – my feeling being that the microwave is more likely to be used ‘independently’ from the rest of the facilities. If one had a 6kW cooker and a 3kW combi-microwave on separate circuits, there’s no doubt that the circuits concerned would have to be designed to be able to supply at least 14.8A and 10.9A respectively – a total minimum current requirement of 25.7A. If, without physically moving any of the appliances, one then moved them onto the same circuit, and regarded them as ‘one appliance’ for the purpose of diversity, the circuit would then only have to be able to supply 18.7A.
Although I understand the statistical basis, I’m not convinced that it is ‘reasonable’ (‘within the spirit of diversity’) to say that the group of appliances require (‘on average’) 7A less when connected to the same circuit than when supplied separately. That would require (statistically) that “7A’s worth” of highs and lows of the microwave demand would cancel with those of the rest of the cooking appliances – perhaps unlikely given that even the maximum load of the microwave is only 13A. Before you say it, I realise that one could use the same argument across the hob and (maybe two) oven(s) of a cooker, but it feels to me far more in the spirit of diversity to regard them (together) as ‘a single appliance’ (to which diversity can be applied) than it does if there are two separate ‘cookers’, or ‘a cooker’ and a combi-microwave.
I suppose one way of looking at what I’m saying about the ‘spirit’ is that the further one moves from having a single ‘cooker’ (be it a single product or a combination of ‘singles’), the more one moves in the direction of the non-residential category of the OSG, where diversity calculations become much less generous (100%+80%+60% of rest) – on that basis, a 6kW cooker plus a 3kW combi-microwave would have an after-diversity current demand of 36.4A, not the 22.6A in a residential environment, and three 6kW cookers would have an after-diversity demand of 62.4A, not 30.4A.
I imagine that you are going to disagree with most of the above and say that we should just ‘blindly’ follow the OSG guidance as regards diversity (despite its lack of ‘explanatory detail’), without any consideration for the actual situation and/or our personal perception of the ‘spirit’ of diversity – but I will nevertheless be interested to hear your view.
Kind Regards, John
), even if the OSG's guidance might be interpreted as say that I could (if I applied diversity across all three).
