If you used the 9.5 kW shower in that period ... would you be comfortable using a design current of 26 A for the final circuit feeding the shower?

I think to answer the question 'What is the maximum demand?' one must first ask 'Maximum demand for what purpose?'

Regulation 311.1 accepts that it may be necessary to determine maximum demand for the whole installation, or a part of it.

I think there are also differences between the maximum demand (as used by the DNO) and the maximum demand (used to rate the consumer unit).


Now, if you were recording 15 minute values, and you had a 10 minute shower, it would of course be reasonable to see a 15-minute demand value of 26.3 A (calculated for shower rated at 240 V) if little else was being used at that time. It may well be reasonable for the DNO to use this value to rate their supply max demand, because it takes a while for cable to heat up  ... but we need to be careful because this assumption is not necessarily applicable to switchgear, for example.

Other appliances (except lights) shown in the list don't necessarily use all their current all of the time, and may well show well below their maximum ratings when looked at in terms of 15 minute or half-hour values. The immersion is perhaps the big exception - if it's used much at all.

If you used the 9.5 kW shower in that period ... would you be comfortable using a design current of 26 A for the final circuit feeding the shower?

I think to answer the question 'What is the maximum demand?' one must first ask 'Maximum demand for what purpose?'

Regulation 311.1 accepts that it may be necessary to determine maximum demand for the whole installation, or a part of it.

I think there are also differences between the maximum demand (as used by the DNO) and the maximum demand (used to rate the consumer unit).


Now, if you were recording 15 minute values, and you had a 10 minute shower, it would of course be reasonable to see a 15-minute demand value of 26.3 A (calculated for shower rated at 240 V) if little else was being used at that time. It may well be reasonable for the DNO to use this value to rate their supply max demand, because it takes a while for cable to heat up  ... but we need to be careful because this assumption is not necessarily applicable to switchgear, for example.

Other appliances (except lights) shown in the list don't necessarily use all their current all of the time, and may well show well below their maximum ratings when looked at in terms of 15 minute or half-hour values. The immersion is perhaps the big exception - if it's used much at all.