PEN Fault Detection
Most UK families are wired with a PME system (Protective Multiple Earth), where the earth wiring runs to a main supply point connected to a neutral conductor which is earthed at multiple points. These systems have the potential for a rare fault called neutral failure, where an upstream disconnection due to degrading or corrosion could increase the risk of electric shock.
PEN Fault Detection: For TN-C-S systems without grounding at the user’s end (as shown above), when the PEN line to the household is cut off due to a line fault and the rear end of the PEN line is in suspension without repeated earthing, and the distribution box RCD is not working properly at this time, the voltage of the protective ground PE is equal to the voltage of the fire line L.
If not equipped with this protection,the shell of the EV in charging will be charged with a voltage equal to the fire line L
voltage. If there are no other appliances except the EV charger, the leakage current will exceed 30mA and the person will not be able to disengage himself, which is a safety hazard; if there are even other appliances, the leakage current can easily exceed 100mA, which is very fatal.