Literature from one manufacturer claims that their unit, which is 7Kw single-phase, provides open pen protection in accordance with 722.411.4.1 (iii) but does not require an earth electrode. If the claim is correct, am I missing something? For compliance with that indent, I thought that the only way it could be done was to provide a measurement electrode unless the unit was three phase.
in accordance with 722.411.4.1 (iii) but does not require an earth electrode. If the claim is correct, am I missing something? For compliance with that indent, I thought that the only way it could be done was to provide a measurement electrode unless the unit was three phase.
AMD1 (2020) introduduced indent (iv) which covers this kind of approach - basically it opens if the L-N voltage is outside the 207 to 253V range - so really they should be claiming compliance with that rather than (iii) these days (or possibly (v) which appears to cover any other approach they haven't yet thought of).
I does seem to be a slightly flawed approach though - where the single phase supply is derrived from a 3-phase distribution system it's possible in some circumstances for a broken PEN in the 3-phase part to leave the L-N within the acceptable range even though N/PEN/PE is itself at a hazardous voltage above true earth. Hence it's only allowed on single phase installations - on 3-phase ones it's not permitted as the artificial N approach is then practical and far more reliable. Some manufacturers attempt to mitigate the shortcomings by additionally monitoring the current in the EV's c.p.c. and opening if it looks to be approaching 30mA - but whether that might trip over diverted N currents on a PME system if the car bodywork happens to have contact with something connected with true Earth (an open door touching a metal bollard for example) has yet to be seen.
in accordance with 722.411.4.1 (iii) but does not require an earth electrode. If the claim is correct, am I missing something? For compliance with that indent, I thought that the only way it could be done was to provide a measurement electrode unless the unit was three phase.
AMD1 (2020) introduduced indent (iv) which covers this kind of approach - basically it opens if the L-N voltage is outside the 207 to 253V range - so really they should be claiming compliance with that rather than (iii) these days (or possibly (v) which appears to cover any other approach they haven't yet thought of).
I does seem to be a slightly flawed approach though - where the single phase supply is derrived from a 3-phase distribution system it's possible in some circumstances for a broken PEN in the 3-phase part to leave the L-N within the acceptable range even though N/PEN/PE is itself at a hazardous voltage above true earth. Hence it's only allowed on single phase installations - on 3-phase ones it's not permitted as the artificial N approach is then practical and far more reliable. Some manufacturers attempt to mitigate the shortcomings by additionally monitoring the current in the EV's c.p.c. and opening if it looks to be approaching 30mA - but whether that might trip over diverted N currents on a PME system if the car bodywork happens to have contact with something connected with true Earth (an open door touching a metal bollard for example) has yet to be seen.
