Yes, in my view we should be considering the energy waste resulting from voltage drop. Most domestic sub circuits are either lightly loaded, or are heavily loaded only briefly. EV chargers are an exception.


The loss of 9 volts at 30 amps is of course 270 watts, or 270 KWH a year if the charger is used for 1,000 hours a year. That could cost about £40 a year.

Halving this loss by use of larger cable is therefore worthwhile. In ten years, larger cable could save £200.


Is there not a proposed regulation under which the designer of an installation is required to consider energy losses ?

I agree, this could be a major issue.  Whilst the equipment might work fine on lower voltages there will be extended periods of charging at full power.  Apart from the cost of the losses, figures like 5% are more than half of the transmission and distribution network losses combined (say circa 8-9% for domestic use).  All this power has to be generated and at times when the system is stretched the marginal costs can be considerable (last week IIRC system costs exceeded £1000/MWh (i.e. £1.00 a kWh) and these costs end up in consumer prices sooner or later.  If losses could be kept down this would reduce bills directly and indirectly by reducing the marginal costs of generation.

There is some interesting work led by Imperial College on the network losses in the service cables that connect homes to the main in the street that shows that these comparatively short cables are responsible for a surprising proportion of system losses and I dare say equivalent arguments apply to the cables feeding EV charging points.  This work predates EV charging which will aggravate the issue so overall there is a lot at stake.  I hope that the DNOs are considering service cable losses as part of their net zero planning.

I agree - This is what the proposed Chapter 81 (proposed in DPC for 18th Ed) and Chapter 82 (proposed in DPC for 18th AMD2) in BS 7671 are all about addressing.


These Chapters may not be part of BS 7671 at the moment, but they have been published for use as BS HD 60364-8-1 and BS HD 60364-8-2. (If you've got a spare £500 or so).

VD = 7.3 mV/A/m so that gives a cable length of (9/0.0073)/32 = 38.5 m.


If you want to reduce the losses by at least 50%, you will need 16 mm² cable. For SWA, price difference at TLC is about £5/m = £200 for 40 m. VD is reduced from 9 to 3.5 V so losses are reduced by 165 W, which costs about 3 p per hour. So the payback point is at 6700 hours.


Presumably EVCPs can cope with 16 mm² cable?

In my view, 3 phase should become the norm for most new domestic services.

A 7Kw  EV charger with a single phase 400 volt input (connect between any two phases) would have an input current of less than 20 amps. Use of all 3 phases would be better still, with a load of about 10 amps per phase.

For the larger household with multiple EVs, three phase is a virtual requirement.

Is a payback period of 6700 hours, worthwhile? In most installs, it is unlikely the car will use 7000 kWh/ year, thus the payback period would probably outlive the car. This is the trouble with just looking at the energy loss, and what is wrong with the BS HD 60364-8 specs, their only idea is to reduce overall consumption at whatever cost. A proper cost/benefit analysis  (although mentioned) is often a finger in the air exercise, it is the same with electric motors and VFDs, the tradeoff is never that clear cut unless it is a 24/7 operation. Changing every property to 3 phase (unless required by foolish ideas on changing everything to electric) would cost a huge amount of money, say £1000 per property x 30 million = 30 billion pounds to save a tiny amount of electricity in the bigger picture. Stupid!

I believe that WPD now require all domestic service cables to be ducted in 38 mm inside diameter approved duct.


Too many brick paved front gardens I suspect...........


Regards


BOD

Sometimes 50mm. It has to be  their approved smooth walled duct and not the usual corrugated type.

broadgage:

In my view, 3 phase should become the norm for most new domestic services.

 

I couldn't agree more, at least for properties bigger than a certain size. The newest development hereabouts allows 25 m² per adult.


However, I couldn't quite see a TPN board in most entrance halls. And a lot of sparks seem to be afraid of it.


And customers don't seem keen. Daughter is going to have an annex and garage built including EVCP and swimming pool heat pump, but so far I have failed to get any sort of engagement about the wiring. I guess if the architect said that she needed it, that would be fine, but his plans have already sliced through all the cables to the kitchen, etc. and the main bonding!