Has anybody used these matt-e products for EV charging points?

Hi John, the important thing to remember about our technology is the way we measure the N-Vn voltage, of course an imbalanced load will have an impact with the Neutral intact but not generally sufficient to create a ‘dangerous’ touch voltage, If the voltage were to rise above the 70v threshold then we will disconnect either with the Neutral connected or disconnected. The important measurement is 70v which can be detected either through Earth or a combination of the phase voltage configurations, simple single phase measurements cannot detect an open PEN conductor in all situations, hence 722.411.4.1 (iv) devices are currently not permitted on installations with a 3 phase incoming supply.

If you have all 3 phases present, loaded or not,  you can create a pseudo-earth at the junction of 3 equal reactances one fed from each phase. 3 small capacitors Y normally does the trick.

 Some simple electronics can look at the offset between that pseudo-earth point and the supplied CPC or neutral (or both) and raise an alarm or fire a shunt trip as required if the offset goes outside expected limits.

Such a detector  circuit also operates if the earthing is fine but the 3 phase voltages are badly out of whack, e.g. something like one phase is at less than ⅔ of the voltage of the others,  but disconnecting that condition is probably not such a bad thing either.

Mike.