V2L Earthing - how?

[kiwi]

Isolation transformer already proposed in post #78.

 

[Staffex]

Isolation transformer already proposed in post #78.

That post concerned supplying a house from the car via a V2L lead.

John Ward is exploring a safe way to operate an outdoor domestic EV charger from a premises with a TN-S or TN-C-S supply. He concludes that a very large earth mat is required but I suggested that a cheaper alternative might to feed the EV charger from a large isolating transformer in conjunction with a single earth rod.

At present, installers typically connect 7 kW outdoor Type 2 chargers to the domestic mains supply via a 40A MCB. Although the chargers have internal RCDs John's video shows how under certain fault conditions this level of protection is wholly inadequate. Ultimately we may see an amendment to the IET 18th edition regulations...

 

[Tim Green]

Staffex does offer a good solution to providing a fully floating supply which can then be used to supply a car charger. In fact, removing any earth might be a better solution than using an earth rod - keep the whole thing floating. The problem is size and cost, as a 3kW isolating transformer is quite large and expensive.

 

[Staffex]

Staffex does offer a good solution to providing a fully floating supply which can then be used to supply a car charger. In fact, removing any earth might be a better solution than using an earth rod - keep the whole thing floating. The problem is size and cost, as a 3kw isolating transformer is quite large and expensive.

Tim, I think an earth rod should be included if a transformer is used. Here's my reasoning...

At around 33' into John's video he shows that, in the event of a break in the supplier's neutral, the indoor neutral - and indoor earth conductor which is strapped to it on a TN-C-S supply - could approach the potential of the live. In that situation John's large outdoor earth mat with its low impedance to true earth would safely sink the fault current. The potential on the earthed casing of an outdoor charger would be kept low, avoiding a nasty shock in the unlikely event that simultaneous contact was made with an outdoor tap etc.

Substituting a 7kW isolating transformer avoids the need for John's large earth mat. But obviously the outdoor casing of the charger cannot be connected to the indoor earth conductor - which as he shows could rise way above true earth potential. However, connecting the charger's earth to an earth rod would cause sufficient current to flow to trip the charger's RCD should a leakage fault occur between the primary and secondary windings of the transformer.

For myself, if I had an outdoor charger I wouldn't bother with either of these solutions to a situation that in practice is highly unlikely to occur. Nor do I imagine that anyone who has an outdoor charger will rush out to excavate 10-20 m² of their garden or driveway in order to bury an earth mat! The IET might not be of the same opinion but fortunately any changes to the regs will not be implemented retrospectively.

 

[Tim Green]

Breakdown isolation voltages on isolation transformers is very high, and even higher on medical devices. It is a risk I would prefer in order to keep an isolated supply which could remain isolated right through the charger.

However, as you say, the risk in any normal set-up is pretty low. A few years ago the regulations for car chargers insisted on an earth rod, but I guess further analysis showed this to be a false remedy.

My Podpoint box is external, but the box is plastic, the car connector and cabling are fully insulated, and the car body is not connected to any external or internal power source. So the risk of shock would require several faults - not impossible but unlikely.

 

[Staffex]

Breakdown isolation voltages on isolation transformers is very high, and even higher on medical devices. It is a risk I would prefer in order to keep an isolated supply which could remain isolated right through the charger.

However, as you say, the risk in any normal set-up is pretty low. A few years ago the regulations for car chargers insisted on an earth rod, but I guess further analysis showed this to be a false remedy.

My Podpoint box is external, but the box is plastic, the car connector and cabling are fully insulated, and the car body is not connected to any external or internal power source. So the risk of shock would require several faults - not impossible but unlikely.

Thanks Tim. You whetted my appetite and I found that Podpoint go into some detail here: Why Pod Point homechargers do not require an earth rod | Pod Point

It seems they've covered all bases. A relay isolates the earth feed to the car in the event of a significant potential developing between E&N. And another relay isolates L&N to the car if a non-standard potential appears between them, as might occur with a break in the neutral between the substation and the premises.

 

[AliveandKicking]

hello everybody.
I want to connect my MG4 via a V2L to some electrical equipment. this equipment is not using more as 2,500W but I'm wondering, if I need a powerbreaker and earth leakage circuit breaker between the MG4 and the Electrical equipment in case of short cuircuit
Thanks for your reply.

 

[Staffex]

hello everybody.
I want to connect my MG4 via a V2L to some electrical equipment. this equipment is not using more as 2,500W but I'm wondering, if I need a powerbreaker and earth leakage circuit breaker between the MG4 and the Electrical equipment in case of short cuircuit
Thanks for your reply.

My MG5 halts the V2L discharge if it detects an earth (PE) leakage of just over 1mA, which is 30 times more sensitive a typical RCD. See post #87 here: V2L Earthing - how?

 

[deanhalllincoln]

Using V2L to supply an entire house.