Diversity settings for apartment blocks and ADMD standard norms

The 15 minute or 30 minute values for MD used by the DNO are not always suitable to size fuses, switchgear/controlgear assemblies and cables for an electrical installation to BS 7671.

values for MD used by the DNO are not always suitable to size fuses, switchgear/controlgear assemblies and cables for an electrical installation to BS 7671

Indeed, and the corollary is also true, that BS7671 methodology is not really suitable or applicable to the design of large distribution networks supplying unsynchronised loads and at power levels where items like transformers and switchgear have thermal time constants of several hours; and a far more nuanced understanding is needed.

It's not clear if the OPs query falls into that situation or not.

The example above of the immersion heaters is amusing - the cheaper fix would have been to randomise the timer settings but it also highlights the problem of a coherent load step versus a random noise-like one (to borrow some terms from the signal processing folk) - and things that accidentally drive group behaviour, like a large group all getting home off the same train, or all staying up late to watch the same football match, tend to break the assumption of randomness , and can cause a very large peak-to-mean variation in demand. Its the difference between kids splashing about incoherently in the pool and synchronising their kicking to produce one big wave.

The saving grace is that the peaks for cooking and so on are normally short compared to the thermal response time of the larger circuit elements like substations.

Mike

It should also be noted that the supply industry is pushing consumers to synchronise changes in demand through various forms of dynamic pricing.

To take the immersion heater example, if the flats were such that Economy 7 was the best tariff then there would almost certainly be a similar surge at whatever the E7 switch on time was.  Meters with switching elements try to ameliorate the effect on the transmission network by incorporating different delays  between notional E7 tariff start time and switching element operation across the meter population but this doesn't help in the distribution network as once switched on an immersion heater is probably going to be running for several hours.

Similarly, most electric car chargers incorporate a random delay in switching if they have been set up in a timed operation mode.

It should also be noted that the supply industry is pushing consumers to synchronise changes in demand through various forms of dynamic pricing.

To take the immersion heater example, if the flats were such that Economy 7 was the best tariff then there would almost certainly be a similar surge at whatever the E7 switch on time was.  Meters with switching elements try to ameliorate the effect on the transmission network by incorporating different delays  between notional E7 tariff start time and switching element operation across the meter population but this doesn't help in the distribution network as once switched on an immersion heater is probably going to be running for several hours.

Similarly, most electric car chargers incorporate a random delay in switching if they have been set up in a timed operation mode.

DShutt said:

It should also be noted that the supply industry is pushing consumers to synchronise changes in demand through various forms of dynamic pricing.

Such as British Gas's half price between 10:00 and 16:00 on Sundays. Just about time to wash and dry a load of laundry.

It may relieve the network of pressure during the working week, but it might place quite a buden on transformers in residential areas. However, as Mike reminds us, they are not going to overheat in 6 hours.