I've been pondering the Protective conductor current (M3) detection method. On the surface it seems like a very good idea - given that basic L-N voltage monitoring to detect open PENs has some gaping holes in it when fed from a 3-phase distribution system.

Anyone know why 21mA was chosen? - seems a odd given that most existing RCD designs & components will be based on 30mA (with actual tripping >15mA ≤30mA) seem to be in the same ballpark and normally proves adequate for additional protection.

EV c.p.c.s look to be quite "interesting" in terms of the current they may carry. As well as conventional fault currents and the normal AC leakage currents (e.g. filters on the AC side of the charger) there's presumably the possibility of some DC components in there from various sources. The PP and CP lines are mostly DC and return via the c.p.c., but I presume the intention is that the monitoring should be upstream of the return connection point though - to avoid those currents in normal service. Plus of course the current resulting from a raised PEN potential running to Earth via someone touching the car - which is what we're trying to detect.

Presumably all these other currents have the potential to desensitize or blind a coil monitoring the c.p.c. in the same way as in a normal RCD? So should we be looking for "types" of monitoring that mirror the RCD requirements for EVSE? e.g. A-type minimum (or possibly F-type considering one of the pilot lines can carry a 1kHz signal?) and B-type if there's nothing to prevent d.c. components of the current exceeding 6mA?

Also am I right in thinking the method won't work well with charge points with exposed-conductive-parts that are in contact with Earth (or an extraneous-conductive-part)?  e.g. most public charge points (either stand alone or bolted onto lighting columns). If the monitoring only covers the c.p.c. out the vehicle, then there's no protection for someone touching the charge point (and going to all this effort to protection someone from shock when they touch the car seems a bit pointless if they're going to run exactly the same risk when they try to plug in or unplug it from the charge point). And if the monitoring includes the connection to the charge point metalwork, it's going to nuisance trip so often as to make it unworkable? (e.g. if the charge point had a resistance to Earth of say 100 Ohms (probably not unreasonable for something embedded into concrete in the ground)  the PEN would only have to get to 2.1V from true Earth to have 21mA flow - e.g. PEN voltage drop along DNO PEN line alone can often be much higher than that in normal service.

   - Andy.

I've been pondering the Protective conductor current (M3) detection method. On the surface it seems like a very good idea - given that basic L-N voltage monitoring to detect open PENs has some gaping holes in it when fed from a 3-phase distribution system.

Anyone know why 21mA was chosen? - seems a odd given that most existing RCD designs & components will be based on 30mA (with actual tripping >15mA ≤30mA) seem to be in the same ballpark and normally proves adequate for additional protection.

EV c.p.c.s look to be quite "interesting" in terms of the current they may carry. As well as conventional fault currents and the normal AC leakage currents (e.g. filters on the AC side of the charger) there's presumably the possibility of some DC components in there from various sources. The PP and CP lines are mostly DC and return via the c.p.c., but I presume the intention is that the monitoring should be upstream of the return connection point though - to avoid those currents in normal service. Plus of course the current resulting from a raised PEN potential running to Earth via someone touching the car - which is what we're trying to detect.

Presumably all these other currents have the potential to desensitize or blind a coil monitoring the c.p.c. in the same way as in a normal RCD? So should we be looking for "types" of monitoring that mirror the RCD requirements for EVSE? e.g. A-type minimum (or possibly F-type considering one of the pilot lines can carry a 1kHz signal?) and B-type if there's nothing to prevent d.c. components of the current exceeding 6mA?

Also am I right in thinking the method won't work well with charge points with exposed-conductive-parts that are in contact with Earth (or an extraneous-conductive-part)?  e.g. most public charge points (either stand alone or bolted onto lighting columns). If the monitoring only covers the c.p.c. out the vehicle, then there's no protection for someone touching the charge point (and going to all this effort to protection someone from shock when they touch the car seems a bit pointless if they're going to run exactly the same risk when they try to plug in or unplug it from the charge point). And if the monitoring includes the connection to the charge point metalwork, it's going to nuisance trip so often as to make it unworkable? (e.g. if the charge point had a resistance to Earth of say 100 Ohms (probably not unreasonable for something embedded into concrete in the ground)  the PEN would only have to get to 2.1V from true Earth to have 21mA flow - e.g. PEN voltage drop along DNO PEN line alone can often be much higher than that in normal service.

   - Andy.

true. And there are credible fault scenarios with damage to the charging leads where the uni-polar square wave "pulsed DC", if you like,  in the cable out to the car does enter terra -firma, and some fraction of it does sneak back via the supply side wiring as well, so we cannot assume 'never' for the  pilot signal ending up 'visible' and confusing to the rest of the ADS.

It is fair tp say that all of these 'M' methods have some blind spots - which is why there is no clear winning method.

Mike.