3198
THE NEW ZEALAND GAZETTE.
[No. 76

room, or obstructed in any manner by resistance-frames,
meters, or otherwise. If space is required for resistance-
frames or other electrical apparatus behind the board, the
passage-way must be widened accordingly.

No cable shall cross the passage-way at the back of the
board, except below the floor or at a height of not less than
7 ft. above the floor.

The space at the back of the switchboards shall be properly
floored, accessible from each end, and, except in the case of
low-pressure switchboards, must be kept locked up, but the
lock must allow of the door being opened from the inside
without the use of a key. The floor at the back shall be
firm and even.

308. Every generator shall be provided with a switch on
     each pole between the generator and the bus-bars.

Suitable instruments shall be provided for measuring the
current and pressure of each generator.

Every feeder connected to the bus-bars in the generating-
station shall be furnished with an ammeter on the main
switchboard.

309. If the transmission-lines from the generating-station
     to the shaft or mine-entrance are overhead, there shall be
     lightning-arresters in connection therewith.

310. Automatic cut-outs must be arranged so that when
     the contact lever opens outwards no danger exists of striking
     the head of the attendant. If unenclosed fuses are used
     they must be placed within 2 ft. of the floor, or be otherwise
     suitably protected.

Where the supply is at a pressure exceeding the limits of
medium pressure, there shall be no live metalwork on the
front of the main switchboard within 8 ft. of the floor or
platform, and the space provided under Regulation No. 307
of this section shall be not less than 4 ft. in the clear. In-
sulating floors or mats shall be provided for medium-pressure
boards where live metalwork is on the front or back.

311. All terminals and live metal on machines over medium
     pressure above ground, and over low pressure under ground,
     where practicable, shall be protected with insulating covers
     or with metal covers connected to earth.

Cables.

312. All conductors inside a mine, except as hereinafter
     provided, shall be continuously covered with insulating-
     material.

A continuously insulated cable must be so constructed
that when a test-piece of it has been immersed in water for
twenty-four hours it will, while still immersed, in the case of
cables intended for low or medium pressures, withstand
2,000 volts for ten minutes between the conductor and the
water, and between cores if there are more than one in the
cable.

If the cable is intended for high or extra-high pressure,
twice the working-pressure shall be taken for the test.

Prior to the immersion the test-piece must have been bent
six times (three times in one direction and three times in the
opposite direction) round a cylindrical surface not more than
twelve times the diameter of the finished cable.

313. The sectional area of conductors must be greater
     than that determined by the heating effect of the current
     required for the maximum number of motors or other
     current-using apparatus that can be used simultaneously
     on the circuit, except in the case of overhead wires upon
     the surface.

The size of the conductor will be determined in accordance
with the table showing maximum current for copper con-
ductors set out in Regulation No. 338, column 3 of which
refers to cables having insulations of Class A, and column 4
to cables having insulation of Class B, according to the
following definitions :—

(A.) A dielectric which is impervious to moisture, and only
needs mechanical protection (“dielectric” does not
include braiding or taping).

(B.) A dielectric which must be kept perfectly dry, and
therefore needs to be encased in a waterproof sheath,
generally of soft metal such as lead drawn closely
over the dielectric.

Below ground, however, column 4 may be applied to cables
having insulation of Class A, in cases where the atmospheric
temperature never exceeds 100° Fahr.

314. All conductors (except as hereinafter provided) shall
     in every case be maintained completely insulated from earth,
     but it is permissible to use the concentric system with earthed
     outer conductors if proper arrangements are made to reduce
     the danger from fire or shock to the minimum, but the neutral
     point of polyphase systems and the middle wire of three-wire
     continuous-current systems may be earthed at one point.

315. Unless fixed as far as is reasonably practicable out of
     reach of injury, all conductors, other than armoured cables,
     must be further protected by a suitable covering. Where
     lead-covered cable is used the lead shall be earthed and
     electrically continuous throughout.

The exposed ends of cables where they enter the terminals
of switches, fuses, and other appliances must, as far as is
reasonably practicable, be properly protected and finished off,
so that moisture cannot creep along the insulating-material
within the waterproof sheath, nor can the insulating-material
if of an oily nature leak out of the cable.

316. All joints must be mechanically and electrically
     efficient, and, where reasonably practicable, must be suitably
     soldered. Wires, other than blasting wires or cables, must
     not be joined by merely twisting them together.

317. Overhead bare wires on the surface must be efficiently
     supported upon insulators and clear of any traffic, and pro-
     vided with efficient lightning-arresters.

318. All cables used in shafts must be highly insulated and
     substantially fixed. Shaft cables not capable of sustaining
     their own weight shall be properly supported at intervals
     varying according to the weight of the cable. Where the
     cables are not completely boxed in and protected from
     falling material, space shall be left between them and the
     side of the shaft that they may yield and so lessen a blow
     given by falling material.

319. Where the cables in levels or main haulage-roads
     cannot be kept at least 1 ft. from any part of the truck or
     tram, they shall be specially protected. When separate
     cables are used they shall, if reasonably practicable, be fixed
     on opposite sides of the road.

The fixing with metallic fastenings of cables and wires not
provided with metallic covering to walls or timbers is pro-
hibited.

Where main or other roads are being repaired, or blasting
is being carried out, suitable temporary protection must be
used, so that the cables are reasonably protected from
damage.

320. Trailing cables for portable machines shall be specially
     flexible, heavily insulated, and protected with either galvan-
     ized steel-wire armouring, extra stout braiding, hose-pipes,
     or other effective covering. Trailing cables shall be examined
     at least once in each shift by the person in charge of the
     machine, and any defects in them promptly repaired.

Except as hereinafter provided, at points where the flexible
conductors are joined to the main cables, a fixed terminal
box must be provided, and a switch shall be fixed close to or
in the terminal box capable of entirely cutting off the supply
from the terminal box and motor.

Suitable clips may, however, be used for the temporary
connection of portable motors where the voltage does not
exceed low pressure.

Switches, Fuses, and Cut-outs.

321. Fuses and automatic cut-outs shall be so constructed
     as effectively to interrupt the current when a short circuit
     occurs, or when the current through them exceeds by 200
     per cent. the working-current in the case of motors, or by
     100 per cent. the permissible current of the cables which
     the fuses protect. Fuses shall be stamped or marked, or
     shall have a label attached indicating the current with which
     they are intended to be used, or, where fuse-wire is used,
     each coil in use shall be so stamped or labelled. Fuses shall
     only be adjusted or replaced by an authorized person.

322. All switches, fuses, and cut-outs must have incom-
     bustible bases of marble, slate, or porcelain. All live parts
     of switches, fuses, and cut-outs not in machine-rooms, or in
     compartments specially arranged for the purpose, must be
     covered. These covers must be of incombustible material,
     and must be either non-conducting or of rigid metal, and, as
     far as practicable, clear of all internal mechanism.

323. Except as provided in Regulation No. 320, all points at
     which a circuit other than those for signals has to be made
     or broken shall be fitted with proper switches. The use of
     hooks or other makeshifts is prohibited.

Motors.

324. All motors, together with their starting resistances,
     shall be protected by switches capable of entirely cutting off
     the pressure and fixed in a convenient position near the
     motor, and every motor of 50-horse power or over in a
     machine-room underground shall be provided with a suitable
     ammeter to indicate the load put upon the machine.

325. Where the unarmoured cables or wires pass through
     metal frames or into boxes or motor-casings, the holes must
     be substantially bushed with insulating bushes, and, where
     necessary, with gas-tight bushings which cannot readily
     become displaced.

326. Terminal boxes or portable motors must be securely
     attached to the machine, or be designed to form a part
     thereof,