Hong Kong Regulations

USE OF ELECTRIC POWER ON THE TRAMWAY RULES - RULE 4

One of the two conductors used for transmitting energy from the generator to
the motors shall be in every case insulated from earth, and is
hereinafter referred to as the "line"; the other may be insulated throughout
or may be uninsulated in such parts and to such extent as is provided in the
following rules, and is hereinafter referred to as the

"return".