It’s time for me to resurrect this discussion, as the IET have published the draft 

Electrician’s Guide to Domestic Electric Vehicle Charging Equipment Installation

and asked for comments, see the post on this forum 

 RE: Have your say on the Electrician’s Guide to Domestic Electric Vehicle Charging Equipment Installation 

I actually watched the video being discussed when this discussion was started by lyledunn 

and paid particular attention to what Simon Ogborn 

said during his conversation with Mark Coles about electricians who think they can design electric vehicle supply equipment (EVSE) electrical circuits in the same way that they design electric shower circuits, they may be responsible for the house burning down, because they are not resistive loads, they are constant power loads.

I see this guidance is in the draft of the new Electrician’s Guide.

If you don’t want to watch the whole video start from 26:45 minutes.

youtu.be/v6n79VAtqV8

Well, it's all about diversity, which you cannot apply to an EVCP.

My agreed (imposed) after-diversity maximum demand on a 3-phase 100 A supply is 30 kVA, which does not leave a huge amount of headroom if I have a car which can draw 22 kVA (most cannot).

I know that petrol is expensive, but if you really are nudging the 100 A limit on a single-phase supply for any length of time regularly, your bills are going to be a bit eye-watering.

This part of the video 

So what is the supplier's fuse for?

We all know that it will not blow at 101 A. Presumably the main function is to protect the tails/DB in the event of a fault, which should be exceedingly rare.

Will it adequately protect a 100 A rated CU against overload?

"Burn your house down" is perhaps a bit of an exaggeration.

"Burn your house down" is perhaps a bit of an exaggeration.

Cable ratings are far more complex than the tables suggest, and folk get very hung-up on changes of a few % and I'm always a bit skeptical of folk who do. as it suggests a blind obedience to the printed word, and a lack of practical experiment. In reality the variations from environment utterly dwarf the effect of 10%  more or less current.

Oddly for something at  work today I have spent some time stuffing currents between 25 and 30A into 1.5mm2 PVC insulated singles that for some very good reason or another are exposed to the air all round, and have no sheath or enclosure. 

Tables might suggest the lab would have burnt down in an instant, but in fact after about half an hour at 30A, the 1,5mm2 single was no more than blood warm. However when twisted with another of its kind identically loaded, it was too hot to hold comfortably after a similar test period. 

Don't worry its not mains, and its not for the UK, but I did smile as it rather illustrates the gap between apparent and real current handling and why grouping and cable sheaths conspire to muddy the water.

Another one I recall was the use of some 2.5mm2 to jump start my car (all 3 cores in parallel for each jumper so about 7mm2 or so.) The cranking current of 300 or so amps had no bad effect on the cable, as it was all over in a few seconds, but the alarm installer chap who was helping me, with the donor battery was convinced I be toasted.

I have occasionally come across a shower wired in 2.5mm2 that is pristine, and others where the cable is vastly oversize, but it has burnt section at one end, presumably started by a grotty termination.

I'd not be expecting a 33or 36A  charger to actually be damaging 4mm2, and clipped direct and ungrouped, I'd expect even 2,5mm2 to suffer no more than a bit of premature ageing. Bur the end in the consumer unit, or in any boxing with other cables,  might well struggle.

Mike.

Hi,

I am willing to be told I am mistaken but my understanding is that EVs (using AC charging controlled according to IEC61851 - which is pretty much all AC charging today) are constant current loads, not constant power?

EVSE tells the EV a maximum current value, not a maximum power.  A standards conforming EV should reduce charging power (linearly rather than with v squared)  with lower supply voltage.

As a result I would expect power dissipation in a cable supplying AC EVSE to be independent of supply voltage.

I keep seeing people (and now apparently guidance documents) stating that EVs are constant power so I must be missing something...

Hi,

I am willing to be told I am mistaken but my understanding is that EVs (using AC charging controlled according to IEC61851 - which is pretty much all AC charging today) are constant current loads, not constant power?

EVSE tells the EV a maximum current value, not a maximum power.  A standards conforming EV should reduce charging power (linearly rather than with v squared)  with lower supply voltage.

As a result I would expect power dissipation in a cable supplying AC EVSE to be independent of supply voltage.

I keep seeing people (and now apparently guidance documents) stating that EVs are constant power so I must be missing something...

DShutt said:

using AC charging controlled according to IEC61851

Useful point. It's easy to get suckered into common misunderstandings of old, solved problems.

I found the google AI info and linked article interesting. Sounds like we should be worrying elsewhere??