Max demand always was a bit of a movable feast - regardless of what we consider normal in BS 7671, DNOs often calculate things on the basis of around 10A per house (averaged over a decent number) . The energy monitor in my house very rarely gets above 7kW even with electric hob & double oven, kettle, toaster, washing machine etc etc - so I'd be perfectly happy that my cut-out fuse would survive adding a 32A EVSE without problem (and I happen to know it's 80A rather than 63A, so even more margin). I don't have an instantaneous electric shower though.

Hopefully most EV charging will be done off-peak, so less likely to coincide with other heavy loads (storage heaters excepting of course) and really the requirement isn't to keep the instantaneous load below the cut-out rating - but rather the thermal equivalent current - so modest "overloads" can persist for perhaps several hours without causing any problems. I'm sure we've all seen places with two or three instantaneous electric showers on an 60A DNO fuse that's never blown - regardless of what the OSG might say.

Or to look it it another way, my house (before I had it) had clearly been heated by storage heaters - there must have been 6 or 7 heaters in the house - and all on together for several hours every night in winter - a much higher load than an EV and a duration likely no less - and that survived fine.

So my gut feel is that an ordinary domestic with non-electric heating is going to be fine, instantaneous electric showers, kettles etc. are unlikely to be on long enough to be a significant problem. If  there're other major long-hour loads - say a heat pump for space heating (or storage heaters), or an electrically heated outdoor hot tub, I'd maybe be thinking twice, but otherwise just go-ahead.

   - Andy.

I agree with all of the above. Experience tells us it is unlikely to be an issue. But it would be non compliant would it not. As the max demand calculated according to official publications would certainly be over 60A, probably over 80A, and possibly over 100A. Do the DNO have anything to in this? I know they have be notified of the install of an EVSE in advance if the max demand is over 60A.

But it would be non compliant would it not. As the max demand calculated according to official publications would certainly be over 60A, probably over 80A, and possibly over 100A.

For a non-compliance you'd have to contradict something in BS 7671 itself - and BS 7671 doesn't specify any particular method of calculating max demand. Many designers use differing methods - in commercial for example it's common to use a Watts per sq metre of floor space approach and ignore circuit based calculation all together. In general supporting publications are taken as advise or guidance, and the OSG in particular is notorious for making assumptions that'll err on the side of safety under the worst possible conditions. So in general there's no objection, certainly no non-compliance, in adopting other methods provided they give valid results for your particular situation. I think the OSG specifically used to say in the introduction to the section on diversity that figures were only for guidance and special knowledge and experience could increase or decrease them. Also most of those tables have remained unchanged for many decades - long before the introduction of EVSE.

   - Andy.

It is fair to say that the  DNOs are also wrestling with similar awkward questions.

UKPN EV and Heat pump loads study.  (try the graphs of possible future load growth figures 34 and 35 for size for example )   and A similar thing from Western power's EV strategy but with less pictures.

Some of the forecast load increases are really quite dramatic. Either it will not happen quite as predicted or some seriously thicker cables will be needed in the street.

Mike.