236
Factor of
safety of supports.
Service Bars.
Erection of line conductors
THE HONG KONG GOVERNMENT GAZETTE, JUNE 13, 1930.
(7) The supports, in conjunction with stays or struts if provided, shall withstand the longitudinal, transverse and vertical loads due to the wind pres- sure hereinafter specified without damage and without movement in the ground. In no case shall the strength of a support in the direction of the overhead line be less than one-quarter the required strength in a direction transverse to the line.
The following factors of safety shall apply to each support,-
Material.
Iron or steel
Reinforced concrete
Factor of safety.
These factors of safety shall be calculated on the assumption that all line conductors, cables and wires carried by the supports are at a temperature of 70° F., and that together with the supports they are subjected to a wind pres- sure of 40 lbs. per square foot.
8) Service lines shall be connected to line conductors at a point of support only and shall be fixed to insulators on consumers' premises. Every part of a service line (other than a neutral conductor connected with earth) which is accessible from a building with the use of a ladder or other special appliance shall be efficiently protected either by insulating material or by other means approved by the Director of Public Works.
(9) Where line conductors forming parts of systems at different voltages are erected on the same poles or supports adequate provision shall be made to at different guard against danger to linesmen and from the lower voltage system being charged above its normal voltage by leakage from or contact with the higher voltage system; and the type of construction shall be subject to the prior approval of the Director of Public Works.
voltages
on same
supports.
Inspection an i maintenance of lines.
Materials used.
Factor of safety of line
(10) Every overhead line, including its supports and structural parts, and electrical appliances and devices belonging to or connected therewith, shall be regularly inspected and efficiently maintained.
(11) All materials used shall at the time of erection conform to the speci- fications of the British Engineering Standards Association and the Post Office (London) for the construction of aerial lines, for the time being in force, so far as the same are applicable and are not inconsistent with this regulation.
Part II.-Specific.
(Applicable according to the voltage between line conductors where no part of the system is connected with earth, or according to the voltage to earth where part of the system is connected with earth).
A.-For voltages not exceeding 650 volts direct current and
325 colls alternating current.
(12) The factor of safety of line conductors shall be 2. The factor of safety shall be based on the breaking load and shall be calculated on the conductors. assumption that the line conductors are at a temperature of 70° F. and that
they are subjected to wind pressure of 40 lbs. per square foot.
Minimum height of
(13) The height from the ground of any line conductor (other than a ser- contactors. vice line), earth wire, or auxiliary conductor at any point of the span at a tem- perature of 160° F. shall not, except with the consent of the Director of Public Works, be less than 19 feet across a public road or 17 feet in other positions. A height of 15 feet may be adopted in situations inaccessible to vehicular traffic.
Where a service line is carried across or along a carriage-way, the height of the line from the ground at any part of the carriage-way shall no, except with the consent of the Director of Public Works, be less than 19 feet and 17 feet respectively.
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