CAP. 103]
[r. 39 cont]
Electricity Supply.
to say, in the case of every electric line to be used for a pressure not exceeding 10,000 volts twice the said maximum pressure, and in the case of a line to be used for a pressure exceeding 10,000 volts, a pressure exceeding the said maximum pressure by 10,000 volts; and the company shall record the results of the tests of each main or section of a main.
(3) Every extra high pressure main shall be protected by a suitable fuse or automatic circuit-breaker, but in the case of a concentric main that fuse or circuit-breaker shall not be inserted in any external conductor thereof which is connected with earth.
(4) In every case where an extra high pressure supply is transformed or converted to a reduced pressure, some suitable automatic and quick-acting means shall be provided to protect the reduced pressure circuits from any accidental contact with or leakage from the extra high pressure system, either within or without the transforming or converting apparatus.
(5) All metal conduits, pipes or casings containing any extra high pressure electric line shall be efficiently connected with earth and shall be so jointed and connected across all street boxes and other openings as to make good electrical connexion throughout their whole length.
(6) Every portion of any extra high pressure electric line placed above the surface of the ground, otherwise than in a sub-station, or in any subway not in the sole occupation of the company, shall be completely enclosed either in a tube of highly insulated material embedded in brickwork, masonry or cement-concrete, or in strong metal casing efficiently connected with earth.
(7) (a) Where extra high pressure mains for three-phase supply consist of insulated conductors laid together, provision shall be made to ensure that neither the ground nor any neighbouring electric line or conductor can become charged by leakage from any such main.
(b) Where this provision is made by a copper strip under a lead sheath that strip shall be not less than sixteen-thousandths of an inch in thickness, and where it is made by steel wires outside a lead sheath
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