Hong Kong Regulations

USE OF ELECTRIC POWER ON THE TRAMWAY RULES - RULE 6

When any uninsulated conductor laid between or within 1 m of the rails forms
any part of a return, it shall be electrically connected to the rails at
distances apart not exceeding 30 m by means of copper strips having a
sectional area of at least 40 mm2, or by other means of equal conductivity.
(L.N. 156 of 1977)