2 electricity supplies to one building

The main fuse, the meter, the henley block  and the consumer unit all say 100A on them


That may well be, but what does your supplier say? Regulation 132.16 states that no addition or alteration, temporary or permanent, shall be made to an existing installation, unless it has been ascertained that the rating and the condition of any existing equipment, including that of the distributer, will be adequate for the altered circumstances.


The main fuse feeding your "street" may be 400 A so what would happen if four of your neighbours did the same?


Regards


BOD

The installer did a “virtual survey” and “load assessment” plus  got approval from the distribution company before agreeing to do the installation. This highlighted the fact I was potentially near 100A as a theoretical max usage already if several things were in use at once and hence the need for the additional charge limiting box.

The only off street parking I have is in the garage so that is where the charger has to go. I cannot park outside the garage as I would block the access road which is narrow. The charger will be within reach of the light switch unless that is moved.

Hmm. So in a way the load management is in the installer's play book. however, I presume he has no easy way of knowing if the same thing has been done on a number of houses on the same substation already . Arguably that is SEP (Someone Else's Problem) until the day it is not.

Just for background.

Be aware that a 100A fuse holder often has a 60A or 80A fuse in it - there is one size of standard fuse holder, but like the fuse in the 13A plug  there is often a smaller one fitted, especially in areas where supply is a bit 'tight' .

It may amuse you to realise that on a housing estate there may be 50-70 houses on each of the 3 phases of your local substation, and although each house has a  fuse as above , the fuse covering the whole phase at the transformer end will be 400, 600 or maybe 800A depending on the transformer size, but seldom more. It all works because folk take short showers and cook dinner at different times,  oh and the fact that the fuses and the transformer are chunky things and  take ages to heat up, so can ride through 100% overload for the odd half hour if required so long as there is some cooling down time afterwards.

Quite a few folk are slightly concerned that if electric cars really take off then there will need to be a lot of transformer upgrades. (and there are literally hundreds of thousands of substations in the UK, some lightly loaded ,sure, others however are quite near the knuckle already. The odd pole-pig round here has the paint blistered off and now going rusty, so preventive maintenance is clearly a bit remiss.)

Mike.

MHowell:

The main fuse, the meter, the henley block  and the consumer unit all say 100A on them.

This doesn't necessarily mean that the supply is capable of supporting 100A, just that the individual bits of equipment can. For example a cut-out may say "100A BS 1361", but that just means the maximum fuse it can support. It may well have an 80A fuse it. Unless the sticker actually says "100A fuse installed" then you can't know without enquiry to the DNO (who won't know and will fob you off), or to the supplier, who may come out and pull out and inspect the fuse (or an electrician might do the same while no one is watching).

It may be easiest to relocate the light switch and socket, or it may be best to have their earthing re-organised, without seeing the site, it would be hard to say.

Once there is an earth electrode, there is no good wiring reason not to use it for the lights and sockets earth as well as the EV.

Mike.

This doesn't necessarily mean that the supply is capable of supporting 100A, just that the individual bits of equipment can. For example a cut-out may say "100A BS 1361", but that just means the maximum fuse it can support. It may well have an 80A fuse it.


What colour is the cut-out? Grey or black?


Regards


BOD

Has the anti-EV brigade taken over this forum?

There's no problem running an EV charger off an 80A supply.  Or a 100A supply that can only supply 100A for short periods.


Not at all, just engineering!


Regards


BOD