Sept. 25.] THE NEW ZEALAND GAZETTE. 2989

ammeter, and if at any time the current exceeds one-thousandth part of the maximum supply-current steps shall be immediately taken to improve the insulation of the system.

(c.) High-pressure three-phase circuits may be either delta-connected or star-connected. If star-connected the neutral point may be earthed at the point of supply and at the neutral point of each star-connected transformer in the circuit, and the insulation of the circuit shall be effectively maintained at all other points. In delta-connected systems or star-connected systems with insulated neutral an approved automatic apparatus must be provided and maintained for effectively earthing any phase-wire in case of accidental contact.

(d.) Extra-high-pressure circuits may be either delta-connected or star-connected. In the latter case the neutral conductor may or may not be earthed. In the case of delta-connected systems or star-connected systems in which the neutral conductor is not earthed, approved means shall be provided in each circuit for indicating faulty insulation in any part of the circuit, and if the insulation of any circuit is faulty immediate steps shall be taken to make good the insulation.

(e.) In the case of a star-connected system of any voltage the neutral conductor of which is connected to earth, the resistance between that conductor and earth shall be sufficiently low to ensure that the fuse or automatic circuit-breaker in any main shall disconnect the circuit from the source of supply in the event of an accidental earth occurring on that main.

(f.) Where any part of a circuit is normally connected with earth, no switch, fuse, or circuit-breaker shall be inserted in the earthed conductor or in any conductor connected thereto, and the connection with earth shall be efficiently maintained, except when it is interrupted by means of a link for the purpose of periodical tests.

(g.) Within a radius of not less than six miles from a telephone exchange the earth may, with the previous consent of the Minister of Telegraphs, be used as the neutral return for transformers not exceeding 20 kilowatts.

7. EARTH CONNECTIONS.

A test shall be made by the licensee every twelve months to ensure that the earth-wires are intact and the earth connections are effective. Such tests shall be made oftener than once in every twelve months if so required by the Minister. Between the electric line or electrical apparatus to be earthed and the general mass of earth the electrical resistance of each separate earth connection shall not exceed 10 ohms, and shall be as much less than 10 ohms as is required to ensure at all times an immediate and safe discharge to earth of electric energy. Records shall be kept of all tests made.

8. SWITCHBOARDS.

(a.) All power-house and substation switchboards, including the frames to which they are attached, shall be made of fireproof material; and the maximum permissible current and temperature in any conductor mounted thereon or leading thereto shall not exceed the values permitted under the rules made from time to time by the Institution of Electrical Engineers of Great Britain. No conductor at a pressure above 650 volts shall be exposed on the front of any switchboard; and the back of any switchboard shall be screened and made inaccessible except to authorized persons.

(b.) All power-house and substation switchboards controlling high-pressure or extra-high-pressure circuits shall be provided with two efficient and independent earth connections, connected in parallel, to which all frames, instrument-cases, and other metal parts thereof shall be connected. Means shall be provided for testing the resistance between these two connections through the earth. Such tests shall be made at least once a month, and shall be recorded.

(c.) Every switch intended to be used for breaking a circuit, and every circuit-breaker, shall be 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.

(d.) All switchboard circuits shall be so arranged that the course of any main conductor may be readily identified.

(e.) Every power-house or substation switchboard shall be erected in such a position as to provide, in front and behind the switchboard, the clear and unobstructed spaces hereinafter mentioned, namely :—

(1.) Low-pressure switchboards—a vertical clearance of at least 7 ft. from the floor to any bare conductor, and a horizontal space or width of at least 3 ft. from each side of the switchboard or any bare conductor affixed thereto.

(2.) High-pressure and extra-high-pressure switchboards other than operating desks or panels working solely at low pressure—a vertical clearance of not less than 8 ft. from the floor to any bare conductor, and a horizontal width or space of not less than 3 ft. 6 in. on each side of the switchboard or any bare conductor or other apparatus affixed thereto.

9. RUBBER GLOVES, MATS, ETC.

Rubber gloves and mats and rubber-soled boots shall be provided for use when necessary.

10. CIRCUIT-BREAKERS.

All outgoing feeders and distributors from any power-house or substation shall be provided with automatic circuit-breakers or fuses set to open at 100 per cent. excess current over the maximum rated load of such feeder or distributor, with a time-limit not exceeding 10 seconds.

11. FUSES.

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

12. REGULATION OF PRESSURE AND FREQUENCY.

The pressure shall be maintained within 5 per cent. above or below the nominal pressure at the consumers’ terminals; and on complaint by any consumer that the variation in voltage exceeds the limits specified, or on the instructions of the Inspecting Engineer, the licensee shall connect a recording voltmeter, to be provided and maintained by the licensee, to record the pressure between the service-lines. If the variations thus recorded exceed the above limits the licensee shall take immediate steps to comply with this regulation. The frequency shall be maintained within 2½ per cent. above or below the standard of 50 cycles per second.

13. OVERHEAD LINES SUBJECT TO DISCONTINUANCE.

The supply of electrical energy may be effected either by underground or overhead electric lines: Provided that if at any time it is deemed by the Minister to be detrimental to the public safety for overhead conductors or any particular class of conductors to remain, the licensee shall at his own expense, upon receipt of a notification to that effect from the Minister, within such time as the Minister thinks fit, replace the overhead conductors by underground conductors, and thereupon the use of the overhead conductors shall be discontinued.

14. STRANDING OF CONDUCTORS, AND MINIMUM SIZE.

(a.) Copper conductors may be either single or stranded. Aluminium conductors must in all cases be stranded.

(b.) The diameter of any conductor in any electric line laid or erected for the supply of electrical energy shall not be less than 0·104 in. (No. 12 S.W.G. or 7/20 S.W.G.): Provided that No. 14 S.W.G. may be used for service connections in spans not exceeding 66 ft.

15. STRESSES IN OVERHEAD LINES.

The stress in overhead conductors shall not exceed the following limits: 25,000 lb. per square inch for hard-drawn copper, 12,500 lb. per square inch for hard-drawn aluminium, 34,000 lb. per square inch for steel, and 22,500 lb. per square inch for iron, in the event of a minimum temperature specified in the license and a wind-pressure of 18 lb. per square foot of diametral plane occurring simultaneously in the case of lines erected outside borough and township limits, and 12 lb. per square foot of diametral plane in the case of lines erected within borough and township limits. The span between supports and the sag shall be determined to conform to the above limiting-stresses.

16. CLEARANCES FOR OVERHEAD LINES.

(a.) Overhead electric lines at low pressure shall not in any part thereof be at a less height than 18 ft. from the ground, except as provided in clause 37.

(b.) Overhead electric lines at high pressure shall not in any part thereof be at a less height than 20 ft. from the ground.

(c.) Overhead electric lines at extra-high pressure shall not in any part thereof be at a less height than 23 ft. from the ground.

(d.) Overhead electric lines crossing electric tramway-lines shall have a minimum clearance of 4 ft. above the trolley wire or wires.

(e.) No overhead electric lines shall come within 2 ft. of any other aerial lines or cables, except at a pole and by arrangement between the respective owners of the wires.

(f.) Overhead electric lines shall be so erected as to be inaccessible to any person without the use of a ladder or other special appliance.