Double wound safety transformer for EV supply.

AJJewsbury:

Interestingly no one has suggested a reason why a charging RCD should be DC sensitive.

From what I've been able to gather, it's not safe (at present) to assume that there's any galvanic isolation between the AC mains supply and the vehicle's propulsion battery & associated circuitry when on change - indeed it seems that at least one current model re-uses the charger power electronics in the power train (I'm guessing during regenerative breaking) so it's all quite tightly coupled together. It seems they don't use the traditional chassis return for the d.c. side (at least not for the propulsion system) but as usual with vehicle electrics there's only single insulation between the internal wiring and chassis. While on charge the vehicle's chassis/bodywork is likely to be connected to the supply's protective conductor. So, as one example, a single fault from say the battery circuit (at perhaps a few hundred volts d.c.) to the chassis, while on charge from a conventional TN or TT supply, would potentially mean a d.c. fault current flow from the battery, to bodywork, via the protective conductor to the EVSE and hence via the means of earthing back to the supply N point and then along the N back through the vehicle's charging circuit to the battery -ve. That d.c. fault current would be flowing through the N side of any RCDs within that loop - both on the EVSE circuit and upstream which may also protect other circuits - potentially blinding them (D-loc style) to any imbalance. Similarly faults from within the charging circuit or elsewhere in the vehicles' wiring could mean pulsed rather than smooth d.c. or at a whole variety of driving voltages.

AJJewsbury:

Interestingly no one has suggested a reason why a charging RCD should be DC sensitive.

From what I've been able to gather, it's not safe (at present) to assume that there's any galvanic isolation between the AC mains supply and the vehicle's propulsion battery & associated circuitry when on change - indeed it seems that at least one current model re-uses the charger power electronics in the power train (I'm guessing during regenerative breaking) so it's all quite tightly coupled together. It seems they don't use the traditional chassis return for the d.c. side (at least not for the propulsion system) but as usual with vehicle electrics there's only single insulation between the internal wiring and chassis. While on charge the vehicle's chassis/bodywork is likely to be connected to the supply's protective conductor. So, as one example, a single fault from say the battery circuit (at perhaps a few hundred volts d.c.) to the chassis, while on charge from a conventional TN or TT supply, would potentially mean a d.c. fault current flow from the battery, to bodywork, via the protective conductor to the EVSE and hence via the means of earthing back to the supply N point and then along the N back through the vehicle's charging circuit to the battery -ve. That d.c. fault current would be flowing through the N side of any RCDs within that loop - both on the EVSE circuit and upstream which may also protect other circuits - potentially blinding them (D-loc style) to any imbalance. Similarly faults from within the charging circuit or elsewhere in the vehicles' wiring could mean pulsed rather than smooth d.c. or at a whole variety of driving voltages.