2364
THE NEW ZEALAND GAZETTE.
[No. 48

(4) In a motor-circuit there shall be provided in the immediate vicinity of each motor connected thereto a single-pole switch and fuse or circuit-breaker arranged to operate within 3 seconds with an overload not exceeding 200 per cent. of the rated full-load current of the motor so controlled. The overload within these limits shall be at the discretion of the licensee.

(5) Each motor shall also be provided with an automatic no-voltage release and a series resistance for starting.

(6) The negative conductor shall be continuous throughout its length without a switch, fuse, or circuit-breaker.

CONNECTION OF CIRCUITS WITH EARTH.

35. In medium, low, or extra-low pressure alternating-current systems the connection of circuits with earth shall be made in accordance with the following requirements:—

(a) The intermediate conductor of a medium, low, or extra-low pressure three-wire single-phase system, and the neutral conductor of a medium, low, or extra-low pressure three-phase four-wire system, shall be earthed in multiple—that is, at the point of supply (the generating-station, substation, or transformer) and at one or more other points along the distribution or service line in addition to any connection with earth which may be on a consumer’s premises.

(b) The resistance between any point of the intermediate or neutral conductor and earth shall not exceed the limits prescribed by Regulation 52 hereof.

(c) The neutral point of a medium, low, or extra-low pressure three-phase three-wire system shall be effectively earthed at the point of supply.

36. In medium, low, or extra-low pressure direct-current systems the connections of circuits with earth shall be made in accordance with the following requirements:—

(a) In a three-wire direct-current system the intermediate conductor shall be earthed at the generating-station only, and the current from the intermediate conductor to earth shall be continuously recorded by means of a recording ammeter, and if at any time the current exceeds one-thousandth part of the maximum supply-current steps shall be taken immediately to improve the insulation of the system.

(b) Where the intermediate conductor is earthed by means of a circuit-breaker with a resistance connected in parallel the resistance shall not exceed 10 ohms, and, on the opening of the circuit-breaker, immediate steps shall be taken to improve the insulation of the circuit, and the circuit-breaker shall be reclosed as soon as possible.

(c) The resistance shall be used only as a protection for the ammeter in case of earths on the system and until such earths are removed. Immediate steps shall be taken to locate and remove the earth.

37. In high and extra-high pressure three-phase alternating-current systems the connections of the circuits with earth shall be made in accordance with the following requirements:—

Star-connected Systems with Earthed Neutral.

(a) The neutral point shall be earthed at the point of supply—that is, the generator neutral point or the neutral point of the transformer secondary where change of voltage occurs—and it may be earthed at any other point, provided that no interference of any description is caused by such earthing.

(b) In the event of an appreciable harmonic current flowing in the neutral connection such as to cause interference with communication circuits the generator or transformer neutral shall not be earthed, but a suitable earthing-transformer shall be used.

(c) In unattended generating stations or substations supplying overhead lines earth leakage relays shall be provided, so that in the event of a leak to earth occurring either the faulty line will be cut out or the whole of the system supplied from this station or substation rendered dead.

(d) These leakage relays if connected to individual feeders or lines shall be set to operate with a time lag not exceeding 5 seconds with a current not exceeding 10 per cent. of the full-load rating of the feeder or line, or, if connected between the neutral point of the generator or transformer and earth, at a current not exceeding 1 ampere.

(e) Where under any conditions the use of earth leakage relays may be impracticable such relays may, with the written consent of the Chief Electrical Engineer of the Public Works Department, be omitted.

(f) In continuously attended generating stations or substations a visual and audible indication may be used in place of automatic disconnection of supply. In such case immediate steps shall be taken to remove the fault or disconnect the faulty feeder or line.

Delta-connected Systems or Star-connected Systems with Isolated Neutrals.

(g) In the case of delta-connected systems or star-connected systems with isolated neutrals earthing-transformers or other means approved by the Chief Electrical Engineer of the Public Works Department shall be provided to give an artificial neutral point which shall be earthed. Earthing equipment shall be of sufficient capacity to ensure the effective operation of the protective apparatus.

(h) Similar leakage protection or indication shall be provided for these systems to that specified in paragraphs (c) to (f) of this regulation for systems with earthed neutrals.

38. High or extra-high pressure single-phase systems shall be earthed in a manner approved by the Chief Electrical Engineer of the Public Works Department.

39. Where any part of a supply system other than on a consumer’s premises 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 for the purpose of periodical tests.

40. Notwithstanding anything contained in the last preceding regulation, systems including more than one generator operating in parallel may have the neutral conductor of a three-phase star-connected generator disconnected when necessary to prevent the circulation of local currents:

Provided that, where all the generators are located in one power-house, at least one generator in operation shall have its neutral point connected to earth:

Provided further that, where the generators are contained in more than one power-house, and the power-houses are inter-connected, a neutral point shall be provided at each power-house and earthed, and all such neutral points shall be so arranged that no earth-circulating current will flow between the power-stations.

41. Notwithstanding anything contained in Regulation 39 hereof, the intermediate conductor of a three-wire direct-current system may be earthed through a circuit-breaker with a resistance of not over 10 ohms in parallel, in accordance with Regulation 36 hereof.

42. When the return current of any individual distribution transformer does not exceed 2 amperes, and the transformer supplying the lines and any distribution transformer supplied by such lines are not less than six miles from any telephone exchange, the earth may, with the previous consent in writing of the Minister of Telegraphs, be used to carry the return current of the distribution transformer.

43. If the insulation of any circuit of any system is faulty, immediate steps shall be taken to make good the insulation before the circuit is again placed in service.

EARTHING-LEADS AND EARTHING-CONNECTIONS.

44. (1) Earthing-leads shall be of copper, and in no case of a less cross-sectional area than 0·02 sq. in. (1/·160 No. 8 S.W.G. 7/·064 or 7/16 S.W.G.) outdoors, or 0·0045 sq. in. (7/·029 or 7/22) indoors, provided that galvanized-iron strip not less in cross-section than 1 in. by 1/16 in. or stranded steel cable or copper-covered steel not less in area than 0·02 sq. in. (7/·064 or 7/16 S.W.G.) may be used for earthing line hardware, earthing-bars, or stay-wires.

(2) Earthing-leads of flat copper strip shall not be less than 3/4 in. wide by No. 18 gauge.

(3) Earthing-leads for electrical apparatus shall be of a carrying-capacity not less than one-quarter that of the largest of the conductors to be protected.

45. Where earthing-leads are exposed to mechanical injury they shall be protected by a wooden batten or other suitable guard. Earthing-leads which are led down the outside of poles shall be protected by a wooden casing for a distance of 8 ft. from the ground.

46. (1) Lightning-arresters and earth-leakage relays shall, except with permission in writing of the Minister, each be earthed by means of an independent earthing-lead and earth-connection spaced well apart from each other, and from any earthing-lead or earth-connection used for earthing circuits or equipment.

(2) The earth-connections for the lightning-arresters and earth leakage relays respectively shall, except in the case of pole substations, be placed not less than 6 ft. from each other and from any other earth-connection, and shall on no