Double wound safety transformer for EV supply.

The use of a safety isolating transformer to provide an isolated supply seems to be being criticised here as unsafe in some way. An isolating transformer construction prevents any significant secondary voltage to any part of the primary circuit by class 2 insulation and an earthed screen between windings, so I cannot understand Andy's comment about capacitive coupling. An RCD on the secondary allows the neutral before the RCD to be connected to the earth connection of the car, as the only potentially dangerous scenario would be contact with both the car body and the cable live conductor, or an earth fault between the cable live and real earth AND contact from the car to earth by a person or livestock.  Both of these would trip the RCD, and must be considered as safe as any other equipment outdoors. A broken CNE would not be dangerous as far as the car is concerned, but could be at any other point in the installation where the installation earth and real Earth could both be contacted, although in theory this should not happen. Of course contacting BOTH live conductors in the charge cable would be just as dangerous as anywhere else.


I have commented a number of times on the design error of cars, they should be class 2 and then all these problems go away at very low cost. I am also somewhat dismayed that a DC tripping RCD is needed for AC mains charge supplies as I see no way that a DC danger could occur, at least not if the batteries are isolated from the charge supply. None of the suggested supply arrangements are safe with PME supplies where the neutral is not to be trusted, and the COP is a pretty bad job in many domestic circumstances, where the car may be charged in or close to a garage with significant metalwork connected to the PME earth.

The use of a safety isolating transformer to provide an isolated supply seems to be being criticised here as unsafe in some way. An isolating transformer construction prevents any significant secondary voltage to any part of the primary circuit by class 2 insulation and an earthed screen between windings, so I cannot understand Andy's comment about capacitive coupling. An RCD on the secondary allows the neutral before the RCD to be connected to the earth connection of the car, as the only potentially dangerous scenario would be contact with both the car body and the cable live conductor, or an earth fault between the cable live and real earth AND contact from the car to earth by a person or livestock.  Both of these would trip the RCD, and must be considered as safe as any other equipment outdoors. A broken CNE would not be dangerous as far as the car is concerned, but could be at any other point in the installation where the installation earth and real Earth could both be contacted, although in theory this should not happen. Of course contacting BOTH live conductors in the charge cable would be just as dangerous as anywhere else.


I have commented a number of times on the design error of cars, they should be class 2 and then all these problems go away at very low cost. I am also somewhat dismayed that a DC tripping RCD is needed for AC mains charge supplies as I see no way that a DC danger could occur, at least not if the batteries are isolated from the charge supply. None of the suggested supply arrangements are safe with PME supplies where the neutral is not to be trusted, and the COP is a pretty bad job in many domestic circumstances, where the car may be charged in or close to a garage with significant metalwork connected to the PME earth.