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Tesla granny charger safety features
- Thread starter JonB
- Start date
cryo
Member
It obviously has passed the relevant UK safety tests to be supplied so therefore should be as safe as any other plug in device.
No, it doesn't have PEN fault protection. That's a UK requirement for fixed installations. The biggest risk is if the socket you are plugging into (or other sockets in a ring) is not connected securely or has other faults, leading to high temperatures and potential fire. If you want to use a granny charger regularly then it's best to have a separate circuit for the socket. With a UMC, I'd be tempted to have a (switched) commando socket installed and buy the commando plug for the UMC. UK 13A sockets can't really be relied upon to run 10A for hours on end. A good installation will cope but needs keeping an eye on. A bad one can be dangerous.
I think (I'm not a qualified electrician) that if an electrician were to install a new circuit to a socket that they knew was to be used solely for EV charging (especially outdoors) then the regs could be read to require them to fit PEN fault protection for the circuit?
Yes, you are correct re: electrician installations of Commando sockets. He is coming round this afternoon. Too bad I told him what the socket was for!
Of course, I could just tack on a Commando myself (to my garage ring's consumer unit which is some 50m from the consumer unit in the house) and linit it to 16A... but I'd always be worried. I do wonder if in-garage EV charging is treated as if it were outside from the regulation POV.
Of course, I could just tack on a Commando myself (to my garage ring's consumer unit which is some 50m from the consumer unit in the house) and linit it to 16A... but I'd always be worried. I do wonder if in-garage EV charging is treated as if it were outside from the regulation POV.
I guess that having a commando socket and PEN fault protection installed might cost around £300. A charge point installation, with the PEN fault detection in the charge point, might only be around £600, after grant. Does it make sense for you to go straight for the charge point, or are there other issues preventing that?
True, inside is inside. But Edition 18 of the regs effectively says that all EV charge points must be fitted with PEN fault protection (either in the charge point or separately) or with a ground rod / mat. There's no distinction between whether the charge point is inside or outside.
Jason71
Well-Known Member
(Rant Warning)
I'm unclear why Edition 18 is so concerned, unless of course the authors believe that PME systems are not to be trusted. Given that in most houses the secondary earth is to water and gas pipes and increasingly that pipework contains sections of plastic I'm not surprised. Some years ago we had some earthing issues and a small potential between neutral and earth so I fitted an earth spike close to the consumer unit and connected it to the ground bars of the consumer unit. End of problems....
We also have an AGA TC stove, this can pull 32A for several hours.... it has its own spur from the consumer unit and at no point did the electrician even check the earth and negative.
So, my view is that as long as there is a proven and reliable earth at the consumer unit there shouldn't be any need for PEN protection. I suppose Edition 18 is taking the "better safe than sorry" without any evidence that there is a problem, just that their might be a problem. By the same logic all garages housing petrol engined cars should have both an automatic fire extinguisher and positive ventilation and an alarm triggered by the detection of petrol fumes. Of course this is not required because years of experience means the risks are well understood and such excessive caution is not needed.
(End of Rant)
I'm unclear why Edition 18 is so concerned, unless of course the authors believe that PME systems are not to be trusted. Given that in most houses the secondary earth is to water and gas pipes and increasingly that pipework contains sections of plastic I'm not surprised. Some years ago we had some earthing issues and a small potential between neutral and earth so I fitted an earth spike close to the consumer unit and connected it to the ground bars of the consumer unit. End of problems....
We also have an AGA TC stove, this can pull 32A for several hours.... it has its own spur from the consumer unit and at no point did the electrician even check the earth and negative.
So, my view is that as long as there is a proven and reliable earth at the consumer unit there shouldn't be any need for PEN protection. I suppose Edition 18 is taking the "better safe than sorry" without any evidence that there is a problem, just that their might be a problem. By the same logic all garages housing petrol engined cars should have both an automatic fire extinguisher and positive ventilation and an alarm triggered by the detection of petrol fumes. Of course this is not required because years of experience means the risks are well understood and such excessive caution is not needed.
(End of Rant)
That is exactly why. If I remember correctly, there are 10s of cases of PME failure each year in the UK.
On a 3 phase distribution system using PME the neutral / earth can (and does) go to a high impedance and the houses on the three phases will all keep working, with the return being made through the other phases through the other houses. EVs are about the only large metallic objects connected to earth standing outside in the rain. If the PME goes high impedance (not necessarily totally open circuit) then the car body can go well over 70V - and to full mains voltage if the PME is totally cut.
Of course, when this happens any earthed metal chassis inside the house (such as boilers or AGA cookers) will go to the same voltage and people can get a shock. But its not as risky as standing in a puddle touching the body of a car, which is far lower impedance and puts the voltage across the heart.
Well, finally I have had a chat with my electrician. My feed to the garage has 6mm squared conductors which is great news, but the total load on the 100A feed may preclude a 7kw charger. I can go with a 16A supply (Commando+granny or a proper EV point) but in the case of the latter I’ll need Open PEN fault detection. A day’s labour plus the chosen solution. At the moment I’m leaning toward a proper charge point, maybe a Viridian box. However the Classic box doesn’t seem to have open PEN protection..
Good video, but it fails to cover some key points.
1. Since the 1970s incoming water pipes have been made of plastic, not metal.
2. Since the 1970s incoming gas pipes have been plastic sheathed steel, and more recently yellow plastic.
Our house has such pipes that terminate above ground and then a copper pipe takes over inside the house. It the copper pipe is thenis bonded to an earth wire.. Why? The water and gas pipes, being plastic, don't offer any possibility of conducting electricity!
I get the feeling that those responsible for writing the regulations are terrified of what might happen, not what is likely to happen.
Perhaps it would be better if home EV chargers were prohibited.
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