Hong Kong Regulations

ELECTRICITY SUPPLY REGULATIONS - REGULATION 13

Specifications and requirements respecting lines, line conductors, etc.

PART I

GENERAL

(1) Line conductors shall be copper, aluminium or such other materials as may
be approved by the Director of Electrical and Mechanical Services.

(2) All line conductors at the time of erection shall comply, as regards
elongation, breaking load and elasticity, with the specification of the
British Engineering Standards Association then in force.

(3) The minimum permissible size for copper and other line conductors (other
than service lines) shall be such as to have an actual breaking load of not
less than 1237 lb., the equivalent minimum cross-sectional area and weight per
mile for copper being as follows-

Conductor Cross-sectional area
sq. in. Weight per mile
lb. No. 8 S.W.G. ........................................ 0.0201 409

The minimum permissible size of service line shall be such as to have an
actual breaking load of not less than 816 lb., the equivalent minimum
cross-sectional area and weight per mile for copper being as follows-

Conductor Cross-sectional area
sq. in. Weight per mile
lb. No. 10 S.W.G. ........................................ 0.0129 262

(4) Line conductors shall be rendered inaccessible to any person from any
building or other place without the use of a ladder or other special
appliance. Regard shall be had to the normal use by the occupier of any
premises or land and where necessary (a) the height of the line conductors
shall be increased to provide sufficient clearance for safety in accordance
with such use, and (b) provision as prescribed in paragraph

(14) or (17) shall be made to prevent danger.

(5) Where a line conductor crosses over or under or is in proximity to any
other overhead wire, precautions shall be taken by the company to prevent
contact, due to breakage or otherwise, between the line conductor and the
other overhead wire, or between the other wire and the line conductor:
Provided that this paragraph shall not be deemed to require the company to
take precautions against contact between a broken line conductor and other
auxiliary conductors and earth wires carried on the same support and forming
part of the same overhead line.

(6) Line conductors shall be attached to suitable insulators carried on
supports of iron, steel, reinforced concrete or wood. Special precaution shall
be taken to prevent the corrosion of all metal work at or below the surface of
the ground. (L.N. 236 of 1972)

(7) The supports, in conjunction with stays or struts if provided, shall
withstand the longitudinal, transverse and vertical loads due to the wind
pressure 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 Factor of safety Iron or steel
...........................................................................
..... 3 Reinforced concrete
.................................................................... 4 Wood
...........................................................................
.............. 3

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 degrees Fahrenheit, and that together with the supports they are subjected
to a wind pressure of 40 lb. per square foot. (L.N. 236 of 1972)

(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 Electrical and Mechanical Services.

(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
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 Electrical and Mechanical Services.

(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
specifications for the time being in force of the British Engineering
Standards Association and the Post Office (London) for the construction of
aerial lines, 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 volts
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 assumption
that the line conductors are at a temperature of 70 degrees Fahrenheit and
that they are subjected to a wind pressure of 40 lb. per square foot.

(13) The height from the ground of any line conductor (other than a service
line), earth wire or auxiliary conductor at any point of the span at a
temperature of 160 degrees Fahrenheit shall not, except with the consent of
the Director of Electrical and Mechanical Services, 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 not, except with the consent of
the Director of Electrical and Mechanical Services, be less than 19 feet and
17 feet respectively.

(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 Electrical and Mechanical
        Services; (II) 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 carrying
               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 Electrical and
               Mechanical Services.

   (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 Electrical and
               Mechanical Services. 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 assumption
that the line conductors are at a temperature of 70 degrees Fahrenheit and
that they are subjected to a wind pressure of 40 lb. per square foot.

(16) The height from the ground of any line conductor at any point on the span
at a temperature of 160 degrees Fahrenheit shall not, except with the consent
of the Director of Electrical and Mechanical Services, be less than the height
hereunder stated-

Voltages not exceeding 66000 volts
............................................................. 20 feet Voltages
exceeding 66000 volts and not exceeding 110000 volts .................... 21
feet Voltages exceeding 110000 volts and not exceeding 165000 volts
.................. 22 feet Voltages exceeding 165000 volts
................................................................. 23 feet

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 or
harmless to human beings or animals in the event of it falling, due to
breakage or otherwise. All metal work other than conductors shall be
permanently and efficiently  connected with earth. For this purpose a
continuous earth wire shall be provided and connected with earth at 4 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 connected with earth the resulting leakage current
shall not be less than twice the leakage current required to operate the
devices which make the line dead or harmless to human beings or animals.

(17A) An overhead line carrying a voltage not exceeding 11000 volts may be
erected on wooden poles and any line so erected shall comply with the
requirements of-

   (a)  specification No. 1320 of August 1946, issued by the British Standards
        Institution, with such modification thereto as may be for the time
        being in force; and

   (b)  these regulations, except in so far as they are in consistent with the
        requirements of paragraph (a). (L.N. 236 of 1972)

(18) Where an overhead line is erected along or across a public road or canal
or across a railway all wires including earth wires and auxiliary conductors
shall be placed at the appropriate height from the ground specified in
paragraph (16) for line conductors, and the following additional precautions
shall be taken to prevent danger-

   (a)  in the case of a line erected along a public road or canal (or within
        50 feet thereof) there shall be provided-

        (i)    duplicate insulators supporting the conductors; or

        (ii)   a device to ensure that in the event of a line conductor
               falling it shall be put to earth; or

        (iii)  other means approved by the Director of Electrical and
               Mechanical Services;

   (b)  in the case of a line erected across a public road, canal or railway
        there shall be provided-

        (i)    duplicate insulators for supporting the line conductor and a
               device to ensure that in the event of a line conductor falling
               it shall be put to earth; or

        (ii)   duplicate insulators supporting duplicate conductors tied at
               intervals not exceeding 5 feet; or

        (iii)  other means approved by the Director of Electrical and
               Mechanical Services.

(19) Supports shall be numbered consecutively and each support shall have a
danger notice of a permanent character securely fixed to it. Adequate
provision shall also be made to prevent unauthorized climbing.

(20) All overhead lines shall be removed on ceasing to be used for the
purposes for which they were erected. (L.N. 76 of 1982; L.N. 298 of 1982)