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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 trans- forming 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 con- nected across all street boxes and other openings so as to make good electrical connection 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.) Where extra high pressure mains for three-phase supply consist of insulated conductors laid together, pro- vision shall be made to ensure that neither the ground nor any neighbouring or electric line or conductor can become charged by leakage from any such main.
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, each of those wires shall be not less than one-tenth of an inch in dia-
meter.
Where the mains are enclosed in a lead sheath, that sheath shall be not less than one-tenth of an inch in thickness, and shall be permanently and efficiently con- nected with earth.
(8.) Extra high pressure mains for single phase supply and all cables connected therewith shall consist either of two concentric conductors or of separate conductors. Where concentric conductors are used the insulation shall be maintained efficiently throughout except that the outer conductor shall be connected with earth at one point, and where separate conductors are used, provision shall be made as in the case of maius for three-phase supply to ensure that neither the ground nor any neigh- bouring electric line or conductor can become charged by leakage.
(9.) An extra high pressure electric line shall not be brought into use for the supply of energy before it has been completely laid, properly jointed, examined, and tested, or until it is in the sole charge of the company, and every such line shall during its use be in the sole charge of the company.
(10.) Extra high pressure mains shall not pass through the same street box with other mains, unless they are enclosed in strong metal casing; and street boxes con- taining extra high pressure mains shall not contain pipes for water, gas, or other service, or electric mains belonging to another undertaking, provided that any such street box may contain telephone wires belonging to the company.
(11.) Sub-stations supplied at extra high pressure shall be established in suitable places and shall be in the sole occupation of the company.
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