EV charging

EV charging leads are clever enough to recognise when they have been daisy-chained, and will refuse to connect.

Never run a granny charger from an extension lead.

Get a lead of the correct length, try Tough Leads:

Their leads contain a Type B RCD. Beware that their prices are ex-VAT.

When I looked at mine a few years ago now I thought it might be to do with the lengths of the pins on the control signals, using slightly different connectors on the car, cable and charger, which means that the control signals don't make it through if two cable-type connectors are mated, such as when you try to daisy-chain them.

nib

I bought a 15m granny lead for £90:

My car is a pure EV, and I can't see any need to spend £1000 on getting a 7.4 kw charger fitted. Are you sure you need one for your PHEV?

why don't you use normal 13A extension leads to feed the "Granny Lead"? It's what I do when I visit my daughter.

There's no logical reason why not, the problem is that many extension leads are not engineered to carry 10A or more for hours on end without getting hot or even catching fire.

Sometimes the plug or socket are poor and get hot

Sometimes the cable is too light a gauge and gets hot

Sometimes the cable is wound onto a drum or otherwise constricted and gets got and melts.

Before I got my home charger I was using a 13A charger and experimented with various cables. I ended up making my own with heavy cable and connectors that were found, by trying several, to run cool. Even that would get warm if looped on itself or covered.

So the only advice that can be given in general is: don't.

nib

It’s generally not recommended to connect a granny charger to an extension lead, on a number of grounds such as the lead might remain coiled or the extension lead plug doesn’t have a temperature-sensing capability and could therefore overheat.

By "clever", I assume that means "can notice a different resistance value than expected"?

I was trying to avoid exactly that, the M->F cable has 6mm^2 conductors so would be better at the output end than a 13A extension of typically

There's a 32A lead with interchangeable commando/13A inputs sitting in the local FedEx depot, waiting for Monday delivery. And yes, I'm aware that commando outlets are supposed to be for industrial use not domestic, so there's a switched/interlocked outlet on the way too, at which point I don't really care why BS7671 is on its high-horse.

I thought Type A RCBOs were the new black?

That is what I'm doing temporarily, I just thought the fatter type2 cable would be better than my extension cable, but I have found a relatively short one with 2.5mm^2 cable.

The rain will keep it cool :-P

I don't intend to spend a grand.

I'd rather have 90 minute top-up, than 6 hours. Audi e-tron 32A commando "leads" are available for £110 ish.

That is sensible advice since to many people all extension leads are the same and would be surprised when the cable containing 0.75mm2 cores gets quite hot.

Nothing to do with EV cars, but I made my own extension for outdoor use, with 2.5mm2 Orange cable.

Many caravan cables for 16A sockets have 1.5mm2 conductors. Mine are 2.5mm2

Very sensible. But for charging EVs there are many things to be aware of. Cable carrying capacity is one, not using a coiled cable is another, but an extension lead’s plug/socket combination at the wall outlet is a further matter, as an ordinary plug doesn’t have temperature sensing and so can’t turn the supply down or off if things start to overheat.

A quality granny charger will have these sorts of things built-in, as well as a Type B RCD (6mA DC, 30mA AC); not many leads offered for sale mention this aspect, but perhaps it’s part of the standards they claim to meet.

In a belt-and-braces approach to using a quality granny charger, I have a WiFi temperature sensor placed on top of the wall socket I use, it normally records a temperature rise of 2degC when a long charge is under way.

Notably the cable between the 13A plug and the EVSE lump isn't just normal 3-core flex, it's 3x2.5mm^2 plus 3x0.75mm^2, I presumed a pair were for a thermocouple, is the other one likely to check for broken earth continuity? Also tougher outer sheath. GB/T 33594 Chinese cable spec.

FWIW I put the six-core setup to AI, which returned this:

The six-core cable contains six individual insulated conductors plus the protective earth (may be an insulated earth conductor or an uninsulated earth braid) routed through the plug and charger.

Their typical functions:

Live (L) — Brown: Main live feed from the plug to the charger.

Neutral (N) — Blue: Main neutral return.

Switched Live / Cut-out feed — Black or Brown/Black: Feed to/from the thermal cut-out terminations or inline switch.

Cut-out return / Switched return — Another contrasting colour (often black or blue with marker): Completes the circuit through the thermal cut-out so the fused live can be interrupted.

Accessory / Control (e.g., thermistor/temperature sensor or charge-control signal) — Often white or grey: Carries a sensor or control signal between charger body and plug-mounted cut-out/thermostat.

Second accessory / Sense / Interlock — Often another light colour (white/green, etc.): Used for a second sensor, interlock, or to provide a separate switched-live for a different internal circuit.

Protective Earth (green/yellow): Present separately (either as a seventh conductor or as an earth braid); required if the charger is not double-insulated.

If the 13A plug contains a thermal cut-out, two of the extra conductors are typically used to route the live through that cut-out (feed and return), and the remaining cores are commonly used for temperature sensing or control/interlock circuits between plug and charger.

Yes, I'm using a 2m two-way extension, just checked with my thermal camera and the 13A plugs on the EVSE and the extension are both at 24°C after an hour of charging.

Yes, I'm not worried about it, it just struck me that a mode3 cable that's fatter than my thumb would have been better than a mains lead that's as thin as a pencil, but hey ...

The car can have a schedule, I think the app can override that with a "charge now" feature.

By this time next week, I'll have a 32A commando on its own 4mm^2 radial with a 7.4kW EVSE instead of the 2.3kW EVSE.

Is the socket it's plugged into BS1362-2 rated? If not, keep an eye on it as it will probably burn out at some point and you'll need to replace it. Especially if you leave the granny cable plugged in rather than unplugging it after each use.

Mike

Hopefully the granny charger plug will have a temperature sensor built in that will reduce or terminate the charge if it senses overheating. So although the socket might need replacing, it shouldn’t reach a state of being burned out.

I decided in the end not to fit an EV rated 13 amp socket, but I chose a charger that only draws around 10 amps.

The socket I bought is a metal clad one in a metal wall box, so that's some protection, I guess.

I do unplug the charger.