Vehicle to load - supply a house

[Deanlincs]

Hi guys I was recently ask by a customer if/how his house could be supplied by his electric car. He wants to charge the car at night on low rate and use the car to power the house during the day. The car has a Vehicle to Load facility and can supply mains voltage a.c. To power any ac device, he showed me this by plugging in a special connector to the car charging socket and plugging in his kettle to the other end of the lead. Apparently the car can supply in excess of 4kw.

This got me thinking could this be possible and have been thinking how it could be achieved.

These are my thought and would appreciate your thoughts and ideas:-

installing a three position(mains, off, car) 100A changeover switch in the tails from the meter to the consumer unit and an additional time delayed 100A RCD 100mA to protect the entire instalation is no problem. The earth wire from the car would be connected to the earth terminal in the changeover switch and hence to the main earthing terminal of the house at the cutout. By doing this the mains supply is disconnected prior to the car supply being connected at no point can both supplies be live in the installation at the same time.

My main concern is what would I do about the earthing arrangement that suits both supply types?

He has a TNCS earthing system.The house is approx 25 years old and the consumer unit is a split type with main switch controling all circuits and a 30ma RCD protecting about half the circuits (sockets etc…).

However, as he is on TNCS earth would I leave the main earthing conductor from the Consumer unit connected to the Neutral at the cutout? One one hand the TNCS combined neutral and Earth is a far better return path to earth where current would only flow in the event of a fault in my house. The fault current would be restricted to a maximum of 100mA and then the main RCD would trip. I suppose I could make the main RCD 30mA non time delayed and restrict fault currents even further.

Or

Do I convert the earthing system to a TT system and disconnect the house from the TNCS system at the cutout? This has the advantage that no fault currents would flow along the DNO’s neutral wire but the path to earth would be far higher resistance. Although it does provide protection against any PEN faults even though these are very rare.

Or

Do I leave the TNCS earthing connected and install an additional earthing rod to the main earthing terminal as an additional path to earth? there Is no reason why I cannot do this as many houses converted to TNCS leave the old main earth rods connected. Any fault current would naturally flow along the low resistance PEN conductor but in the event of a PEN fault there is an alternative path back to earth via the earth rod.

I did consider switching the main earth conductor in the changeover switch (would have to be 3 pole) so the installation switches between TNCS (when on main supply) to TT (when on car supply) but the cross sectional area of the main earthing conductor would not be maintained through the changeover switch.

I’m struggling to figure out the correct way to go here if I do it at all. I want to have the right fault protection in the house when connected to mains and don’t want to push current down the DNO’s cables if they has engineers working on them and think they are isolated.

I do like figuring out difficult new challenges and I can see this type of situation coming up more often in the future as electric cars become more popular.

Have I missed something anything that I should be considering?

any thoughts would be gratefully received.

Dean

 

[DMElec.1]

Hi guys I was recently ask by a customer if/how his house could be supplied by his electric car. He wants to charge the car at night on low rate and use the car to power the house during the day. The car has a Vehicle to Load facility and can supply mains voltage a.c. To power any ac device, he showed me this by plugging in a special connector to the car charging socket and plugging in his kettle to the other end of the lead. Apparently the car can supply in excess of 4kw.

This got me thinking could this be possible and have been thinking how it could be achieved.

These are my thought and would appreciate your thoughts and ideas:-

installing a three position(mains, off, car) 100A changeover switch in the tails from the meter to the consumer unit and an additional time delayed 100A RCD 100mA to protect the entire instalation is no problem. The earth wire from the car would be connected to the earth terminal in the changeover switch and hence to the main earthing terminal of the house at the cutout. By doing this the mains supply is disconnected prior to the car supply being connected at no point can both supplies be live in the installation at the same time.

My main concern is what would I do about the earthing arrangement that suits both supply types?

He has a TNCS earthing system.The house is approx 25 years old and the consumer unit is a split type with main switch controling all circuits and a 30ma RCD protecting about half the circuits (sockets etc…).

However, as he is on TNCS earth would I leave the main earthing conductor from the Consumer unit connected to the Neutral at the cutout? One one hand the TNCS combined neutral and Earth is a far better return path to earth where current would only flow in the event of a fault in my house. The fault current would be restricted to a maximum of 100mA and then the main RCD would trip. I suppose I could make the main RCD 30mA non time delayed and restrict fault currents even further.

Or

Do I convert the earthing system to a TT system and disconnect the house from the TNCS system at the cutout? This has the advantage that no fault currents would flow along the DNO’s neutral wire but the path to earth would be far higher resistance. Although it does provide protection against any PEN faults even though these are very rare.

Or

Do I leave the TNCS earthing connected and install an additional earthing rod to the main earthing terminal as an additional path to earth? there Is no reason why I cannot do this as many houses converted to TNCS leave the old main earth rods connected. Any fault current would naturally flow along the low resistance PEN conductor but in the event of a PEN fault there is an alternative path back to earth via the earth rod.

I did consider switching the main earth conductor in the changeover switch (would have to be 3 pole) so the installation switches between TNCS (when on main supply) to TT (when on car supply) but the cross sectional area of the main earthing conductor would not be maintained through the changeover switch.

I’m struggling to figure out the correct way to go here if I do it at all. I want to have the right fault protection in the house when connected to mains and don’t want to push current down the DNO’s cables if they has engineers working on them and think they are isolated.

I do like figuring out difficult new challenges and I can see this type of situation coming up more often in the future as electric cars become more popular.

Have I missed something anything that I should be considering?

any thoughts would be gratefully received.

Dean

Look up the chap that has done this in the US. Also some thoughts - new CU as a minimum (and SPD) AND of course types or RCD and the backfeed properties they require.... (hence new CU requirments) and 4kW so.... you'd need to have an automated or second switch to offer a second CU to then shut off the first, and have limited circuits supported - (a radial and some lights?/ just a boiler??) Sounds like great fun if it was my retirement project, but I am hopefully awhile away from that. Oh and the earthing........not going to comment on that without full assessment of the property and its environs, manufacturers technical info....is it a smart charger? if it isnt its also not within new gov guidelines, so that may be an issue.

 

[brianmoooore]

Missed this thread the first time around.
What the OP's customer is trying to achieve should be the norm for all EV charge point installs. An expensive, large rechargeable battery sitting outside the house, unused, for the majority of the time, when it could be charging on cheap electricity in low demand periods, and running the house at periods of higher demand (basically all day) when electricity is more expensive. Makes much more sense than installing separate batteries in the house.
The prospect of halving domestic electricity bills would make electric cars make much more economic sense and boost the sales no end.
Shouldn't be manual change over switches involved ,of course. Should all be computer controlled, with the option to program in how many miles you want to drive the car the next day.

 

[DMElec.1]

Missed this thread the first time around.
What the OP's customer is trying to achieve should be the norm for all EV charge point installs. An expensive, large rechargeable battery sitting outside the house, unused, for the majority of the time, when it could be charging on cheap electricity in low demand periods, and running the house at periods of higher demand (basically all day) when electricity is more expensive. Makes much more sense than installing separate batteries in the house.
The prospect of halving domestic electricity bills would make electric cars make much more economic sense and boost the sales no end.
Shouldn't be manual change over switches involved ,of course. Should all be computer controlled, with the option to program in how many miles you want to drive the car the next day. TOTALLY! but it isn't in operation as of now, and in all honesty, at 4kW, that's not really what his charger is for, as I said in my first line, check out YouTube for the chap that has done this already, I can't be bothered to look him up. But it's worth a Google.

 

[Gavin John Hyde]

Check with your DNO as they will have a few questions.
in theory no technical obstacles but we are not quite there yet with a clear agreed process.