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17. Aerial conductors over housetops. —Where necessary to run aerial conductors over the top of any buildings, they shall bo kept at least 7 feet clear above the buildings ; and all poles placed on buildings shall be fixe J in shoes or plate*, so that the downward pressure may bo distributed over a large surface ; such poles must be properly stayed with stranded galvanized-iron or steel wires, and it' of metal be efficiently counected to earth, and if of wood the poles shall be provided with lightning conductors as required by Regulation No. 21 18. Maximum intervals between supports. —Every aerial conductor shall be attached to supports at intervals not exceeding 200 feet where the direction of the conductor is straight, or 150 feet where this direction is curved, or where the conductor makes a horizontal angle at the point of support. If suspending wires are used, as required in Regulation 31, the span for straight lines may be increased to 250 feet. 19. Angle of crossing thoroughfares.— -Wherever possible a conductor should cross a street at right angles, and in no case shall the angle between such conductor and the direction of the street at the place of such crossing be less than 60 degrees, and the span shall be as short as possible. 20. Supports, construction and erection of. —Every support of aerial conductors shall be of a durable material, and properly stayed against forces due to wind pressure, change of direction of the conductors, or unequal lengths of span, and the conductors must be securely attached to insulators fixed to the supports by a non-metallic ligament. The factor of safety for the suspended wires shall be at least 6, and for all other parts of the structure at least 12, taking the maximum possible wind pressure at 35 lbs. per square foot. 21 Connexion of support to earth. —Every support, if of metal, shall be efficiently connected to earth, and every other support which shall be exposed in such a position as to be liable to be affected by lightning shall be protected by a lightning conductor fastened to the support along its entire length, and projecting above the support to a height of at least 6 inches, such lightning conductor to be efficiently connected to earth, and possess a mechanical strength, and offer a passage to electrical discharges equal to that of a strand of seven No. 16 galvanized-iron wires. 22. Lightning arresters. —Lightning arresters of pattern approved by the constituted authorities shall bo placed in the circuit of all aerial conductors at the point where they leave the generating station. 23. Crossing other ivires. —Where any aerial conductor is erected so as to cross one or more telegraph, telephone, or other wires, it may pass over, under, or, where specially permitted by the constituted authorities, between such wires, provided precautions are taken to keep such conductor at least 1 foot clear of the other wires in all directions ; and both the aerial conductor and the telegraph and telephone wires shall be respectively affixed to separate supports, placed within 6 feet of the point of intersection where practicable, but in no case to exceed 10 feet, and further protected from coming in contact, under any circumstances, by guard irons or wires ; all such guard irons or wires to be efficiently connected to earth. 24. Service conductors. —All service conductors shall be laid from the main cable, being joined thereto at a point as near as possible to a pole or support, direct to insulators attached to the building or premises to be served, and lead upward therefrom to tubes or channels of insulating and non-inflammable material, through which they shall pass into the building. Where they run along the outside of any building they shall ba kept at least 12 inches apart, and be affixed to insulators. The tubes or channels to be sloped downwards from the inside to the outside of the building. 25. Maximum 'working current. —The maximum working current in any aerial conductor shall not be sufficient to raise the temperature of the conductor in any part to such an extent as to materially alter the physical condition or specific resistance of the insulating covering, if any, or in any case to raise such temperature to a greater extent than 30° Fahrenheit, and efficient automatic means shall be provided which will render it impossible for this maximum working current to be by any accident exceeded to the extent of 25 per centum, even for short intervals of time ; and special care shall be taken that the cross sectional area and conductivity at joints is sufficient to avoid local heating, and that the joints are properly made and protected against corrosion. 26. High-pressure conductors to he insulated. —Every high-pressure aerial conductor shall be continuously insulated with a durable and efficient material, to be approved by the constituted authorities, to a thickness of not less than one-tenth of an inch, and, in cases where the extreme difference of potential in the circuit exceeds 2,000 volts, the thickness of the insulation shall be increased by onethirtieth of an inch for every 1,000 volts or part thereof. This insulation shall be further efficiently protected on the outside against injury or removal by abrasion. If this protection be wholly or partly metallic, it shall be efficiently connected to earth, so, however, as not to cause undue disturbance to other electric lines or works by electrostatic induction or otherwise. 27 how-pressure conductors to be insulated. — Every low-pressure aerial conductor shall be continuously insulated with a durable and efficient material, to be approved by the constituted authorities, and shall be further efficiently protected on tho outside against injury by removal or abrasion. If this protection be wholly or partly metallic, it shall be efficiently connected to earth. 28. Specification of insulation. —The material used for insulating any aerial conductor must be such as will not be liable to injurious change of physical structure or condition when exposed to any temperature between the limits of 10° Fahrenheit and 150° Fahrenheit, or to contact with the ordinary atmosphere of towns or manufacturing districts. 29. Minimum insulation resistance alloicable — lndicator of leakage. —The insulation resistance of any circuit using high-pressure or extra high-pressure aerial conductors, including all devices for producing, consuming, or measuring energy, connected to such circuit, shall be such that, should any part of the circuit be put to earth, tho leakage current shall not exceed o'o4 of an ampere in the case of continuous currents, or o'o2 of an ampere in the case of alternating currents. Every such circuit containing high-pressure or extra high-pressure conductors shall be fitted with an indicating device, which shall continuously indicate if the insulation resistance of either conductor fall below the conditions required by this Regulation. 30. Earth return.— No earth return shall be allowed on any electric light or power circuit. 31 Suspension, of conductors.' —Every aerial conductor having a sectional area greater than 7, No. 16, S.W.G., shall be suspended, by means of non-metallic ligaments, to a suspending wire, securely affixed to the support, and efficiently connected to earth at every point of support. Every such suspending