The standard supply for a new house seems to be circa 18KVA single-phase. I have a client who needs to make application for a supply for a new build house at 400m2 with the only certain information being that an air source heat pump is to be used for heating. The client simply does not know what the electrical loading might be. The house is only coming out of the foundations but the DNO supply may take many months as the house is in a relatively remote rural location, thus loading details are required before the DNO will consider progressing the proposal. It is a big house, but that is what it is, just a big house. I am inclined to advise a standard supply but 3-phase as with a large AS heat pump, maybe shower, cooking and perhaps an EV or two, 18KVA wouldn't be long being gobbled up. As we move towards a higher reliance on electric as a power source for some heavy current-using equipment, it might be that 18KVA is no longer a realistic standard supply for even the smaller property.
Even a 3 phase 100 amp supply might be marginal with a couple of 22Kw vehicle chargers.
The two EV chargers and the heat pump will use in total about 70 amps per phase. No diversity should be allowed in my view as both the vehicle chargers and the heat pump could run for hours simultaneously.
That leaves only 30 amps per phase for everything else.
A 40 amp shower will overload the phase to which it is connected.
A 30 amp cooker, and a lightly loaded ring final will overload the phase to which they are connected.
A heavily loaded ring final and another lightly loaded ring final will overload the phase to which they are connected.
And to which phase is a second shower, an immersion heater, or another cooker to be connected ? remembering that all three are already potentially overloaded.
And yes I know that the DNO cut out fuse will probably survive such overloads, but it is poor practice to design a new installation on such a basis.
A single phase 300 amp supply would IN THEORY be preferable as diversity works better, but in practice single phase services of that size are almost unknown, and 22Kw vehicle chargers are 3 phase.
It looks to me as though EITHER a three phase 150 amp supply will ne needed, or that the EV chargers should be ones that throttle the charging rate when the rest of the installation is heavily loaded.
Even a 3 phase 100 amp supply might be marginal with a couple of 22Kw vehicle chargers.
The two EV chargers and the heat pump will use in total about 70 amps per phase. No diversity should be allowed in my view as both the vehicle chargers and the heat pump could run for hours simultaneously.
That leaves only 30 amps per phase for everything else.
A 40 amp shower will overload the phase to which it is connected.
A 30 amp cooker, and a lightly loaded ring final will overload the phase to which they are connected.
A heavily loaded ring final and another lightly loaded ring final will overload the phase to which they are connected.
And to which phase is a second shower, an immersion heater, or another cooker to be connected ? remembering that all three are already potentially overloaded.
And yes I know that the DNO cut out fuse will probably survive such overloads, but it is poor practice to design a new installation on such a basis.
A single phase 300 amp supply would IN THEORY be preferable as diversity works better, but in practice single phase services of that size are almost unknown, and 22Kw vehicle chargers are 3 phase.
It looks to me as though EITHER a three phase 150 amp supply will ne needed, or that the EV chargers should be ones that throttle the charging rate when the rest of the installation is heavily loaded.
