JULY 12.] THE NEW ZEALAND GAZETTE. 2367

93. In transformer substations not exceeding 50-kilowatt capacity only the high-tension or primary side of the transformer need be equipped with fuses or circuit-breaker, and special precautions shall be taken in the adjustment of these to the capacity of the transformer.

94. (1) All overload devices shall be set to operate within three seconds at a current not exceeding 200 per cent. of full load of such feeder or distributor, except that in the case of fuses the time stated may be one minute. Where the 200 per cent. of normal full load is not in excess of 2 amperes a fuse to blow at 2 amperes may be used.

(2) In the case of feeders or distributors which supply further subfeeders or subdistributors through automatic circuit-breakers, and where selective operation of such circuit-breakers is desired, the time-setting of the main-feeder circuit-breakers may be increased to fifteen seconds.

(3) Where automatic reclosing switches or circuit-breakers are used they shall not be set to reclose more than twice after any interruption, and the lockout device shall then prevent any reclosing except by hand. The interval between the automatic reclosings shall not exceed 10 seconds.

95. Fuses or circuit-breakers shall not be inserted on the medium or any lower pressure side of transformers when lines are erected in accordance with Regulation 156 hereof, unless the fuses or circuit-breakers are set to open the circuit at a current not less than 25 per cent. greater than that required to operate the fuse or circuit-breaker on the primary feeder to which the transformer is connected, and where such fuses are inserted they shall be renewed at intervals of not more than six months.

96. On star-connected systems with earthed neutral current-transformers Z-connected to two-trip coils shall not be used.

97. Series street-lighting circuits shall be provided with protective apparatus of a type approved by the Chief Electrical Engineer of the Public Works Department, set to operate in the event of a break occurring in the secondary circuit.

CIRCUIT-BREAKERS AND SWITCHES.

98. Every switch, switch-fuse, circuit-breaker, and isolating-link shall be—

(a) So constructed, placed, or protected as to prevent danger :

(b) So constructed and adjusted as accurately to make and maintain good contact :

(c) Provided with an efficient handle or other means of operating insulated from the system, and so arranged that the hand of the operator cannot inadvertently touch live metal :

(d) So constructed or arranged that it cannot, with proper care, be left in partial contact or accidentally fall or move into contact when left out of contact.

(e) Safety catches shall be provided on disconnecting-switches when mounted in such a way that gravity tends to open them, and also when the magnetic forces due to short circuits are of values liable to open them.

99. Every switch intended to be used for breaking a circuit, and every circuit-breaker, shall be so constructed that an arc cannot accidentally be maintained.

100. Every circuit-breaker shall be of the loose-handle type, and capable of breaking the undermentioned currents by hand without undue arcing and without injury to the operator: in the case of direct current it shall be capable of breaking 200 per cent. of the normal full-load current of the circuit on which it is installed, and in the case of alternating current it shall be capable of rupturing the maximum short-circuit current to which it may be subjected.

101. All enclosed switches or circuit-breakers shall have an external device to indicate clearly whether the switch or circuit-breaker is open or closed.

102. All metal handles of high or extra-high pressure switches or circuit-breakers, and (where necessary to prevent danger) all metal not normally connected to the circuit, shall be earthed.

103. Where practicable, switches shall be so wired that the blades will be dead when the switch is open.

FUSES.

104. Every fuse shall be either of such construction or so protected by a switch that the fusible metal may be readily renewed without danger.

STRANDING OF OVERHEAD CONDUCTORS, AND MINIMUM SIZE.

105. In all overhead lines—

(a) Copper conductors used for medium or any lower pressure may be either solid or stranded :

(b) Copper conductors used for high or extra-high pressure shall be stranded :

(c) Galvanized-iron, steel, or copper-covered steel conductors for all pressures may be either solid or stranded :

(d) Aluminium conductors for all pressures shall be stranded.

106. (1) The area of any overhead conductor shall be not less than that shown in the following table, namely,—

• Smallest British size manufactured.

(2) Earthing-leads shall be of the sizes prescribed by Regulation 44 hereof.

107. Joints between conductors shall be soldered or made with suitable clamps or metal sleeves. A dry splice may be made only in stranded conductors which are in tension.

STRESSES IN OVERHEAD LINES.

108. (1) The lines shall be so designed and constructed that the stress in overhead conductors will not exceed—

(a) 25,000 lb. per square inch for hard-drawn copper, or

(b) 14,000 lb. per square inch for annealed copper, or

(c) 12,500 lb. per square inch for hard-drawn aluminium, or

(d) 34,000 lb. per square inch for steel, or

(e) 22,500 lb. per square inch for iron

when subjected simultaneously to a minimum temperature of 20° F. (or such other temperature as may be specified in the license) and at a wind-pressure of 18 lb. per square foot of diametral plane (in the case of lines erected outside borough, town district, and township limits) or 12 lb. per square foot of diametral plane (in the case of lines erected within such limits).

(2) In the case of a composite conductor with a steel core, the maximum load under the circumstances mentioned in the last-preceding subclause shall not exceed 40 per cent. of the ultimate strength of the conductor if the steel core has a diameter of 0·162 in. or less, and 50 per cent. if the diameter of the steel core exceeds 0·162 in.

(3) Where in the opinion of the Minister the lines are liable to be subjected to ice loading, they shall be designed to withstand a wind-pressure of 8 lb. per square foot of diametral plane with a radial thickness of ½ in. of ice, or, with the approval of the Minister, to withstand such other conditions as may be more prevalent in the particular locality.

109. Dynamometers for measuring the tension in the wires, or gauges for measuring the sag thereof, and thermometers for measuring air-temperature during erection, shall be used and maintained by the licensee.

110. Overhead wires shall be strung and pulled up in such a manner that the metal is not damaged thereby, and when come-alongs or draw-vides are used for pulling up the wires they shall be of the parallel-jaw type.

CLEARANCES FOR OVERHEAD LINES.

112. Overhead electric lines erected across street intersections shall not at any part thereof over such intersection be at a less height than 21 ft. above ground-level, and, if so required by the District Telegraph Engineer, shall be erected at such greater height than 21 ft. as he specifies in writing.

113. Overhead electric lines at medium or lower pressures shall not at any part thereof be erected and maintained along or across any street at a less height than 18 ft. above the ground-level, except that lines crossing a footpath at the side of any street or over any place used by the general public for pedestrian traffic only may be at a less height than 18 ft., but not less than 14 ft., above the ground-level.

114. (1) Overhead electric lines at medium or lower pressures erected elsewhere than along or across any street, footpath, or other place mentioned in the last preceding regulation shall be erected and maintained at a height of not less than 16 ft. (if bare) or 14 ft. (if covered) above ground-level: Provided that in the case of service-lines, the height above ground-level in the span between the building and the nearest pole thereto may be not less than—

(a) 14 ft. where the line crosses any way open to the public :

(b) 12 ft. where the line crosses any way used exclusively by vehicles :

(c) 9 ft. in any other part of the span.

(2) For the purposes of the last preceding subclause a bare neutral, if earthed, shall be deemed to be a covered line.

B