Hong Kong Regulations

ELECTRICITY SUPPLY REGULATIONS - REGULATION 37

Connection with earth of a three-wire system

CONNECTION OF CIRCUITS WITH EARTH

Where the pressure of a supply between the adjacent conductors of a three-wire
system of mains exceeds 125 volts the intermediate conductor shall be
connected with earth in accordance with the following conditions-

   (a)  the connection with earth of the intermediate conductor shall be made
        at 1 point only on each distinct circuit, namely at the generating
        station, sub-station or transformer, and the insulation of the circuit
        shall be efficiently maintained at all other parts;

   (b)  the current from the intermediate conductor to earth shall be
        continuously recorded and if it at any time becomes excessive steps
        shall be immediately taken to improve the insulation of the system.