Hong Kong Regulations

USE OF ELECTRIC POWER ON THE TRAMWAY RULES - RULE 13

The insulation resistance of all continuously insulated cables used for lines,
for insulated returns, for feeders, or for other purposes, and laid below the
surface of the ground, shall not be permitted to fall below the equivalent of
6M W/km. A test of the insulation resistance of all such cables shall be made
at least once in each month. (L.N. 156 of 1977)