Updated on 31/07/25 by Abby_OVO
Regarding charging with a ‘granny’ charger. There is a bit more nuance here and a very different reason for not using one of these.
EVs charge at different rates depending on circumstances. The ‘normal’ charging rate is about 7kW. This is dependent upon the charge point being allowed to deliver 7kW if the DNO has approved this. If not you are only allowed it to charge at a maximum of 3.68kW. Why 3.68kW? That is the maximum load that you are allowed to take without prior DNO notification or authorisation. This is why you can plug in a granny charger without prior approval. Some cars like the early Nissan Leafs were only able to charge at 3.5kW.
What is referred to as a granny charger is something that you can plug into a three pin socket, that normally supplies about 2kW to an EV for charging. 2kW is under 10A which is the maximum, continuous safe load you can take from a three pin socket that is in good condition. I know they are rated at 13A but that is not a continuous rating. Remember the 3kW heaters you used to be able to buy that took 12A? Well they are not approved anymore and they can’t be sold legally.
Getting back to using a granny charger, I’m sure Charge Anytime is able to work out how much power is being taken as it can see the increase in power taken and the rate at which the State of Charge is increasing and then cleverly work out how to schedule the charging. However, at 2kW there may not be enough charging slots available to charge to the required level resulting in under-charging but I have seen comments that CA is able to compensate under a lot of circumstances. No, there are much more serious issues with granny chargers that you need to be aware of.
1) Burnt out sockets and fires. Most granny chargers don’t monitor the temperature of the three-pin plug. If the plug/socket pins become contaminated or corroded over time (possibly because they are outside in all weathers, then the increase in the socket/pin contact resistance causes more heat to be generated, leading to more oxidation in a rapid, vicious circle that ends in a burnt out socket and/or fire. Think about that happening in the house.
2) The contactors in the granny charger are necessarily miniature types that tend to have a shorter life that those designed to fit on a DIN rail in a EVSE charger. They can burn out causing extensive damage and sometimes resulting in putting mains voltage on the Control Pilot pin going to the car and blowing up the control electronics in the car. That has happened and it’s a lot more expensive than a proper EVSE unit.
3) The hidden failure. EVSE units have PEN protection if your house has a TN (Terra Neutral) connection. Doesn’t apply if you have a TT (Terra Terra) connection. In a TN connection the earth is derived from the incoming neutral line and rare DNO faults can result in the neutral line being disconnected between you and the substation but generally everything carries on working because the currents travel between the three phases and not the neutral. With a balanced load on all three phases this results in your neutral voltage being very close to the ground potential outside your house. The car bodywork is connected to the house earth (derived from the neutral) unlike something that is normally used outside like a mower which is insulated. In the event of a PEN (Protective Earth Neutral) fault from the substation and an unbalanced load across the phases then the voltage on the neutral can be very different to the local earth voltage. This gives rise to a shock hazard if you touch the body of a car under those conditions. That could cause injury or even be fatal. You probably won’t know when Open PEN faults occur especially if you charge overnight.
The recommendation is that you install a proper, approved EVSE for charging that takes care of all of those issue. You can go down the granny route, like I have by fixing the issues. 1) I use a Commando connector rated for 16A continuous. 2) I have external contactors rated at 20A on a DIN rail. 3) I have installed a Garo Open PEN protection unit that detects that fault condition and opens the live, neutral and most importantly the earth connection when this occurs. I’ve actually had an Open PEN event at my house and the lights were on and varying wildly as the neutral voltage changed with changing loads on the other phases but the Garo unit had isolated the car.
Think carefully about the risks before choosing to use a granny charger for anything other than occasional charging.
Peter
@Blastoise186 @Peter E thanks for the comments, some food for thought there.
I originally ordered and paid for a Hypervolt, but the contractor could not find a way to route the cable from the meter to the required location without going through some original stonework that I didn’t want destroyed. The outcome was cancellation/refund. The situation hasn’t really changed but as we were already planning some building work around the front of the house we decided to pick up the home charger again at that point in time.
For what it’s worth, I chose carefully with the charger we’re using, and this is connected inside the garage into a modern and recently-installed socket/cable/consumer unit.
@Abby_OVO thanks, I contacted the helpline yesterday. Of course, the car charged successfully last night but it would be good to get an explanation of what prevented it previously.
