Could someone help me calculate maximum demand for my house?

[thomp1983]

Hi all, I'm applying to my dno to have my cutout fuse upgraded to 80a ahead of having am evse installed and they want to know the maximum demand.

Both consumer units contain all the following circuits and I've listed the mcb or rcbo size too.

Cooker circuit b40
Downstairs sockets b32
Garage sockets b16
Upstairs lights/garage lights b6
Shower b40
Upstairs sockets b32
Kitchen sockets b32
Air conditioning b16
Pv/solar 32a rcbo

That's all the currently connected circuits and the evse will be added on a 40a rcbo.

I know you apply diversity to the circuits due to not everything being in full use all the time but I don't know how to do all the maths.

Is there any other information required to calculate maximum demand such as number of outlets/sockets on each circuit etc.?

Thanks,
Chris.

 

[Murdochcat]

60A will be fine

 

[ericmark]

I good question, in my own house I have solar, and as a result I have the solar software showing me what I am using.

There is a particular time of the day which is critical, 00:30 to 05:30 when I have off-peak so I run dish-washer, washing machine, tumble drier, and charge batteries. and one can see I have peaked to 4643 kW = 20 amps, using the shower is likely the largest load, bit misleading as shows 5.905 kW but the shower uses more like 8 kW and it is the fact some things show direct and some go to a server so there is a slight time shift, which results in a spot error.

Smart meter used ½ hour blocks so also not that accurate, so the blip over 16 hours shows 0.308 kWh which since in kWh not kW shows very little.

So in real terms, an EV will use 7 kW = 31 amps approx, so the question is what will be used at the same time, with something like Octopus Go your off-peak is 00:30 to 05:30 and the question is what else will be used at that time?

So if we assume by 00:30 you will be in bed, for me there are only three items I could use in those hours, dish-washer, washing machine, tumble drier, unlikely I will take a shower then or cook a meal. So I can't set the time to switch on, I have to set a delay, in either ½ hour or 1 hour slots, depending on how far in advance I am setting them, each has some form of heating, but in the main heating water for a short time, so the chance that two heating elements will turn on together is slim, but possible, but fact is I have never blown the 60 amp DNO fuse, and looking at use over the years since solar and off-peak, I have not seen the software show anywhere near 13.8 kW = 60 amps even when charging my batteries at 4 kW, so your EV will take around 13 amp more than my batteries, so it seems unlikely it will ever exceed 60 amps.

I can understand the DNO asking on a new build, but on existing they should realise the 60 amp existing fuse has never ruptured so adding another 31 amps at night with an 80 fuse, it would be highly unlikely that the 80 amps will every be exceeded.

Theory with two electric showers and a battery I could exceed 60 amps, but I never have.

 

[thomp1983]

The calculator on tradecalcs.co.uk shows a max demand of 139a so I've supplied that figure to national grid and I'll see what they come back with, so far they emailed this morning asking for a photo of the cut out.

I understand that a 60a fuse would be fine as the evse ct clamp will reduce the load if it sees it getting close but if I can have it upgraded to 80a or 100a so I can avoid that situation then I will, I want to be able to use the full capacity of the evse if and when I need to ideally.

Thanks,
Chris

 

[blup]

Technically 60A but upgrade to 100A as the demand for electricity is only going to increase.

 

[flameport]

The calculator on tradecalcs.co.uk shows a max demand of 139a

 

[thomp1983]

Are you suggesting it's wrong John?

 

[flameport]

Rather obviously, if the max demand was 139 amps, the main fuse would have been blown out long ago.