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.
My guess would be that it measures the LE voltage and the NE voltage. LE should be about 230V and NE should be about 0V. Anything else suggests a fault - and it doesn't really matter exactly what the fault is. A completely broken PEN is liable to float at about 115V, especially if there are LE and NE filter capacitors.
In a PME installation in of earthing type TN-C-S, and in some PNB systems, N-E voltage will almost always be zero, so measuring N-PE at the charge point a red herring - it will never show you anything.
The PEN conductor does indeed float about - but not necessarily at 115 V.
If the break is on the single-phase cable to the premises, N will approach the supply voltage to Earth.
If the break is in a three-phase portion of the network, you can get a voltage from 0 (if all phases downstream of the break are balanced) to above 340 V (yes, that's rms ... to Earth ... and I know this is greater than U0, but that's what reactance does for you)
My guess would be that it measures the LE voltage and the NE voltage. LE should be about 230V and NE should be about 0V. Anything else suggests a fault - and it doesn't really matter exactly what the fault is. A completely broken PEN is liable to float at about 115V, especially if there are LE and NE filter capacitors.
In a PME installation in of earthing type TN-C-S, and in some PNB systems, N-E voltage will almost always be zero, so measuring N-PE at the charge point a red herring - it will never show you anything.
The PEN conductor does indeed float about - but not necessarily at 115 V.
If the break is on the single-phase cable to the premises, N will approach the supply voltage to Earth.
If the break is in a three-phase portion of the network, you can get a voltage from 0 (if all phases downstream of the break are balanced) to above 340 V (yes, that's rms ... to Earth ... and I know this is greater than U0, but that's what reactance does for you)
