Provision
to prevent
danger.
Factor of safety of line
THE HONG KONG GOVERNMENT GAZETTE, JUNE 13, 1930.
237
(14) Where the voltage to earth exceeds 250 volts direct current or 125 volts alternating current, precaution should be taken to prevent danger-
(I) from a broken line conductor by the provision of-
(a) a neutral or earthed conductor carried continuously from pole to pole, and so arranged in relation to the other conductors that in the event of breakage of any one of them the line conductor shall make contact with the earthed wire; or
(b) other means approved by the Director of Public Works.
(H) from leakage by the provision-
(a) in cases where metal poles are used, of
(i) an earthed wire, running from pole to pole and connected
to the poles; or
(ii) a suitable metal framework to support the insulators carry- ing the line conductors, the framework being insulated from the pole but connected to the neutral conductor; or (iii) other means approved by the Director of Public Works. (b) in cases where wooden poles are used, of
(i) a bonding wire connected to the supporting metal work of all insulators, the bonding wire terminating at the lowest part of the supporting metal work; or
(ii) other means approved by the Director of Public Works.
All stay wires other than those which are connected with earth by means of a continuous earth wire shall be insulated to prevent danger from leakage. For this purpose an insulator shall be placed in each stay wire at a height of not less than 10 feet from the ground.
B. For voltages exceeding 650 volts direct current and
325 volts alternating current.
(15) 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 a wind pressure of 40 lbs. per square foot.
Minimum height of
(16) The height from the ground of any line conductor at any point on the conductors. span at a temperature of 160° F. shall not, except with the consent of the Director of Public Works, be less than the height hereunder stated :--
Voltages not exceeding
66,000 volts ..........
:20 feet.
66,000 volts & not exceed- ing 110,000 volts.........21 feet.
Voltages exceeding 110,000 volts and not exceeding 165,000 volts Voltages exceeding 165,000
volts.
22 feet.
23 feet.
Voltages exceeding
0
。
Provision
The height from the ground of an earth wire or auxiliary conductor shall not be less than the minimum heights prescribed in paragraph (13) above.
(17) Adequate means shall be provided to render any line conductor dead to prevent in the event of it falling, due to breakage or otherwise.
danger.
All metal work other than conductors shall be permanently and efficiently connected with earth. For this purpose a continuous earth wire shall be pro- vided and connected with earth at four points in every mile, the spacing between the points being as nearly equidistant as possible, or alternatively, the metal work shall be connected to an effective earthing device at each individual support. The design and construction of the system of earth connections shall be such that when contact is made between a line conductor and metal con-