2406
THE NEW ZEALAND GAZETTE.
[No. 48

(e) From the position or positions at which the installation
is earthed concentric wiring shall be employed
throughout up to all fixed positions for fittings or
accessories. At all positions where the external
conductor ceases to surround the internal conductor
the latter shall be separated from the surface upon
which the fitting or accessory is mounted by an
incorrodible metal plate or terminal box to which the
external conductor is electrically connected. This
requirement does not preclude the interposition of a
wooden block between the metal plate and the fitting
or accessory mounted thereon, provided that this
metal plate covers the principal recess in the wooden
block.

(f) Where the metal sheathing of a cable is used as one
conductor the resistance of the sheathing shall not
be greater than that of the inner conductor when
measured at a temperature of 60° F.

(g) Joints in the external conductor, however made, shall
be of such a nature that the conductivity of the
conductor is not reduced.

(h) All circuits, lamps, and appliances shall be controlled
and protected by single-pole circuit-breakers, or
switches and fuses, which shall be inserted in the
internal conductor of the circuit. No circuit-breaker, switch, or fuse shall be included in the
external conductor.

(i) Ordinary accessories may be used, but if lampholders
having central contacts are employed such central
contacts shall be connected to the internal conductor.

(j) Lamp-fittings may be wired with two separate wires,
one being insulated and connected to the internal
conductor and the other to the metal-work of the
fitting.

(k) Twin flexible cords may be used between fixed points
and portable or pendant fittings. If such flexible
cords terminate in plug-and-socket connections these
connections shall be of either the concentric or the
two-pin polarized type.

WIRING-SYSTEM HAVING EXTRA-LOW PRESSURE CONTROL
CIRCUITS.

124. The control-circuit wiring and accessories in wiring
     systems having extra-low-pressure control shall comply with
     the following requirements :—

(a) Remote controlled switches shall have their live parts
enclosed in non-combustible and non-absorbent cases.
They shall be fixed in full view in readily accessible
positions. The insulation resistance between the
supply terminals and the control terminals of the
switch shall be not less than 100 megohms.

(b) All control wiring shall be run entirely apart from the
supply wiring.

(c) The pressure of the control circuit shall not exceed
12 volts. Transformers shall be double-wound with
one side of the secondary earthed and shall be
mounted on the switch or distribution board, and be
controlled by a switch and fuse on the primary side.

(d) Conductors shall be not less than 1/-036 in., having an
insulation resistance of 300-megohm grade, unless
the transformer complies with Regulation 133, in
which case ordinary bell-wire may be used.

(e) Where subject to mechanical injury conductors shall be
protected. When unenclosed they shall be secured
with clips having rounded edges or insulated staples,
but two or more conductors shall not be secured
under the same staple.

(f) Between roof and ceiling conductors may be fastened to
the sides of joists or battens without further protection. Where buried in plaster or concrete they
shall be enclosed in an approved metallic sheathing.
All joints shall be accessible, and be efficiently soldered
and insulated.

(g) Pushes shall be of substantial mechanical construction
and of a type approved by the Chief Electrical
Engineer. The conductors shall terminate in suitable
terminals and be secured by a metal thread screw.

(h) Heating-circuits shall not be controlled by this system
unless fitted with an indicating-device approved by
the Chief Electrical Engineer.

WIRING IN SPECIAL SITUATIONS.

Where Inflammable Goods, or Explosive Dust or Gas is present.

125. (1) In places where highly inflammable goods—e.g.,
     cinematograph-films and petrol are stored or packed, or where
     inflammable or explosive dust or gas is liable to be present,
     incandescent lamps (not exceeding 60 watts) only shall be
     used, and they with their holders shall be enclosed in fittings
     having thick glass globes.

(2) Where inflammable or explosive dust or gas is liable
to be present the fittings shall be gas-tight.

126. (1) The wiring shall be run in screwed steel conduit,
     and where inflammable or explosive dust or gas is liable to be
     present it shall be rendered gas-tight by painting all threads
     with white-lead, red-lead, or graphite pipe-jointing compound
     before screwing into fittings, and all conduit-fittings shall be
     gas-tight.

(2) The conduit shall in all cases be screwed into the lamp-fittings, and no flexible pendant, ceiling-roses, or portable
apparatus shall be used.

(3) Where corrosive gases or liquids are also present, the
proposed system of wiring shall be submitted to the Chief
Electrical Engineer for approval.

127. Switches, fuses, and all accessories liable to arc shall,
     where practicable, be located outside such places as aforesaid,
     but where this is impracticable they shall be of the ironclad
     type, and where inflammable or explosive dust or gas is liable
     to be present they shall be flame-proof.

128. All generators, motors, starters, and their terminals
     and connections shall be enclosed in incombustible cases,
     which shall be flame-proof where inflammable or explosive
     dust or gas is liable to be present.

129. No conductors other than those required for the supply
     and use of current in such places as aforesaid shall be installed.

Freezing-chambers and Cool Stores.

130. (1) Section and distribution boards shall not be fixed
     in freezing or cooling chambers.

(2) Switches shall not be fixed in freezing or cooling
chambers.

(3) No conductors other than those required for the supply
and use of current therein shall be installed in freezing-chambers and cool stores.

Situations Subject to Excessive Heat.

131. (1) Cables insulated with rubber shall not be used in
     situations where the temperature of the conductor would
     exceed 135° F. for short periods, or 120° F. for long periods.

(2) Cables insulated with paper or fibre shall not be used
in situations where the temperature of the conductor would
exceed 176° F.

(3) Where higher temperatures are liable to be experienced,
the wiring shall be in accordance with the requirements of the
Authorized Inspector.

(4) In all cases where the air-temperature does not exceed
80° F. the current density for any size of wire shall not exceed
that prescribed by Table IV or Table V in the Third Schedule
hereto with respect to that size. Where that temperature is
exceeded the current density shall be reduced so that the
maximum temperature of the conductor does not exceed
that stated in subclause (1) or subclause (2), as the case may
be, of this regulation.

BELL AND TELEPHONE CIRCUITS.

132. Cables which are used in connection with the electric
     bells, telephone and signalling apparatus, &c., in a building
     shall be kept away from and not be installed in the same
     casing or conduit as the cables used for the distribution of
     the electrical supply throughout the building.

133. Bell and signalling circuits (except telephone circuits)
     may be operated from the electric-lighting, heating, or powersupply mains, provided that they are connected to the secondary side of double-wound transformers, having a secondary
     voltage not exceeding 12 volts, and further provided that—

(a) Each transformer is mounted on the main switch-board.

(b) Each transformer is protected on the primary side by
a single pole switch and fuse, and one side of the
secondary winding is earthed.

(c) The conductors when unenclosed are secured individually
by means of insulated staples, and where subject to
mechanical injury the conductors are adequately protected.

(d) Joints in the conductors are, as far as practicable,
avoided, but where they are unavoidable they are
staggered, soldered, and efficiently insulated.

(e) The conductors are insulated with vulcanized india-rubber not less than 300 megohm grade, save that
ordinary bell-wire may be used if the transformers
are of a capacity not exceeding 50 watt and so
designed that on sustained short circuit their impedance is such as to limit the current to such a value
as will not burn out the transformer.

SELECTION OF CABLE RUNS.

134. (1) Cables shall be fixed as far as possible in accessible
     positions, so chosen that they are not exposed to drip or
     accumulation of water or oil, or to high temperature from