SEPT. 6.] THE NEW ZEALAND GAZETTE. 2505

(2) Earthing-leads of flat copper strip shall not be less than ¾ in. wide by 18 S.W.G.

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

31-32. 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 not less than 8 ft. from ground-level.

31-33. Where a testing-link is provided in any earthing-lead fixed on a pole it shall be installed not less than 8 ft. above the ground, unless suitably protected to the satisfaction of the Inspecting Engineer so as to prevent electrical hazard.

31-34. (1) Every lightning-arrester shall, except with permission in writing of the Chief Electrical Engineer, be earthed by means of an independent earthing-lead and earth-connection spaced well apart from any earthing-lead or earth-connection used for earthing any circuit or equipment.

(2) The earth-connection for the lightning-arrester shall on no account be interconnected with any earth-connection used for the earthing of any circuit or equipment, and shall, except in the case of pole-substations, be placed not less than 6 ft. from any other earth-connection.

(3) Where in the case of a pole-substation the distance of 6 ft. specified in the last preceding clause cannot be obtained, the distance shall be the maximum obtainable on the sub-station structure.

(4) No earthing-lead for a lightning-arrester shall pass through any iron or steel pipe, and it shall be taken as direct as possible between the lightning-arrester and the earth-connection. Bends shall be avoided where possible, but where a bend is unavoidable it shall have as large a radius as possible.

31-35. On alternating current star-connected systems with the neutral earthed, pipe crossings for medium pressure or any lower pressure electric lines may be earthed by connecting to the neutral.

31-36. The neutral of a medium pressure or any lower pressure three-phase four-wire system may be used for earthing stays, outdoor lamp-brackets, earthing-guards, and other line hardware, provided that it is of a cross-sectional area not less than that prescribed by Regulation 31-31 hereof, or is earthed at points as nearly equidistant as possible and at intervals of not more than 15 chains each.

31-37. Every joint in an earthing-lead shall be soldered or made with a suitable clamp or metal sleeve.

31-38. Every earthing-lead, if and so far as it is laid underground, shall have all joints kept carefully and sufficiently painted or otherwise adequately protected against corrosion, and shall, unless otherwise mechanically protected, be laid slack to prevent it being readily broken.

PART 32.—SWITCHGEAR.

SWITCHBOARDS.

32-01. (1) All power-house and substation switchboards, including the frames to which they are attached, shall be made of durable non-ignitable material of adequate mechanical strength, and the maximum permissible current and temperature in any conductor mounted thereon or leading thereto shall not exceed the values permitted under British Standard Specification No. 159.

(2) All live metal at a pressure exceeding 110 volts which is mounted on the front of any switchboard shall be screened so as to prevent any person making accidental contact therewith, and the back of every switchboard on which is mounted bare live metal at a pressure of 250 volts and over to earth shall be made inaccessible to unauthorized persons by means of screens or otherwise.

(3) Every door leading to the back of a switchboard shall be provided with a spring or other approved device which shall ensure that the door remains wide open when not properly shut and locked.

(4) No equipment shall be mounted on the back of any switchboard if its operation will be hazardous when so mounted.

32-02. (1) 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 metal frames, all metal instrument-cases, and other metal parts thereof not normally alive shall be connected, either directly or through a common earthing bus-bar:

Provided that the metal cases of instruments operated from the secondary winding of instrument transformers having the secondary winding earthed, or which are otherwise suitably protected, need not be earthed.

(2) The resistance through the earth between these two connections shall be tested as specified in Regulations 51-01 and 51-02 hereof.

32-03. (1) A rubber mat of not less than ¼ in. thickness shall be provided for the protection of operators in front of every power-house and substation switchboard—

(a) Which directly controls lines or apparatus working at a pressure above 250 volts to earth; or

(b) Which, being mounted on a floor of conducting material, directly controls lines or apparatus working at a pressure above 100 volts to earth, other than a switchboard of the totally enclosed metal-clad type.

(2) A rubber mat as aforesaid shall be provided in the screened-in space at the rear of every power-house and substation switchboard when such switchboard controls lines or apparatus working above medium pressure, or where such switchboard is mounted on a floor of conducting material, and controls lines or apparatus working at a pressure above 250 volts to earth.

32-04. All switchboard circuits shall be so arranged that the course of any main conductor may be readily identified. The standard colourings and conductor location shall comply with British Standard Specification No. 158.

32-05. All panels shall have marked thereon, near each switch or circuit-breaker, the name of the feeder or apparatus controlled by such switch or circuit-breaker.

32-06. (1) Except in the cases mentioned in the next succeeding clause, isolating-switches shall be fitted in the leads of each panel of all high pressure or extra-high pressure switchboards so that the panel can be made dead when necessary.

(2) The last preceding clause shall not apply—

(a) Where the circuit-breaker can be withdrawn from a sources of supply; or

(b) Where the switchboard consists of one panel and it can be made dead by opening a switch outside and adjacent to the substation; or

(c) Where the switchboard consists of one panel supplied from one generator.

32-07. (1) Every power-house or substation switchboard shall be erected in such a position as to provide in front and behind the switchboard the clear unobstructed spaces hereinafter mentioned namely:—

(a) Low pressure and medium pressure switchboards: An overhead clearance (except in enclosed spaces dealt with in paragraph (c) of this clause) of not less than 7 ft. from the floor to any conductor under which it is necessary to pass, and a passageway in front of the switchboard with at least 3 ft. horizontal clearance from the face of the switchboard or any bare live metal affixed thereto.

(b) High pressure and extra-high pressure switchboards (not exceeding 11,000 volts between phases), other than operating desks or panels working solely at medium pressure or any lower pressure: An overhead clearance (except in enclosed spaces dealt with in paragraph (c) of this clause) of not less than 8 ft. from the floor to any conductor under which it is necessary to pass, and a passageway in front of the switchboard with at least 3 ft. 6 in. horizontal clearance from the face of the switchboard.

(c) In every enclosed space behind any switchboard where only skilled men would be employed when the switchboard is alive (unless all live metal other than that being worked on is suitably screened)—

(i) An overhead clearance of not less than 7 ft. from the floor to any bare conductor under which it is necessary to pass:

(ii) A horizontal clearance of not less than 6 ft. for high pressure or extra-high pressure, and not less than 4 ft. for medium pressure or any lower pressure where it is possible to pass between any live conductors less than 7 ft. above the floor:

(iii) A horizontal clearance of not less than 3 ft. between any live conductor less than 7 ft. above the floor and any wall, screen, or other similar object:

(iv) For all pressures in excess of 11,000 volts, such clearances as are approved.

(2) When a passageway is provided behind any switchboard the horizontal clearance shall be the same as that specified for the front of the switchboard, and shall be measured from any screen erected at the back of the switchboard.

32-08. (1) Every passage-way and enclosed space shall have a firm and even floor.

(2) Adequate means of access, free from danger, shall be provided for every enclosed space or passage-way, and such means of access, enclosed space, and passage-way shall be adequately lighted to prevent danger.

(3) All space at the back of switchboards shall be kept free of rubbish, and shall not be used for storage purposes.