p390-391:Layout 1 15/5/07 13:03 Page 1
i Technical Information
Ambient temperature
TABLE M54G
Conduits shall be suitable for the maximum and minimum values of ambient temperature to which
they will be exposed in normal service.
Cross sectional area, pvc Area required for
insulated copper conductor steel conduit
Where non-metallic or plastic boxes are in contact with a luminaire, they shall be suitable for the S ≤ 16 2.45S
suspended load, and the temperature to which they will be subjected. S > 35 1.23S
522-01-01
546-02-05
Long straight lengths of rigid plastic conduit must allow for expansion and contraction; using slip
joints in plastic conduit is a means of achieving this.
Where a conduit is used as a protective conductor, its electrical continuity has to be assured,
522-12-01
and has to be protected against mechanical, chemical or electrochemical deterioration.
543-02-05, 543-02-04
Colour code
Where conduit is to be distinguished from other services, it shall be coloured orange.
Where a conduit is used as the circuit protective conductor for more than one circuit, it shall be
514-02
sized either by;
1. calculation, using the formula 543-01-03 and the most onerous value of fault current and
Prefabricated systems
disconnection time encountered in each of the various circuits, or
Where conduit systems are prefabricated and not wired in situ, allowance shall be made for
2. selected by using Table 54G, with the cross-sectional area of the largest cable enclosed in
tolerances in the building dimensions. Precautions against damage to such systems shall be
the conduit.
taken, so that the conduits or cable ends are not damaged during erection, or during building
operations.
543-01-02
522-06-01, 522-08, 522-12-01.
When conduit is used as a protective conductor, it shall be protected against mechanical, chemical
and electrodynamic effects.
Fire barriers
543-03-01
Where conduits pass through floors, walls, partitions or roofs, the opening through such walls or
floors etc., shall be sealed to the same degree of fire resistance as that of the material through
The joints in conduit when used as a circuit protective conductor do not need to be accessible.
which it is passing.
543-03-03
527-02-01
Conduit shall not be used as a PEN conductor.
Where conduits pass through walls and floors etc., that have a specified degree of fire resistance,
the hole round the conduit in the wall or floor etc., shall be sealed to the same degree of fire
546-02-07, 543-02-10
resistance. Additionally, the conduit shall be internally sealed to maintain the degree of fire
resistance of the material through which the conduit is passing.
Where a protective conductor is used for both protective and functional purposes, the
requirements for the protective measures shall prevail.
Where the conduit system has a maximum internal cross-sectional area of 710mm
2
, and is a non-
546-01
flame propagating system, it need not be internally sealed. (With the exception of 38mm conduit,
all conduits have an internal area less than 710mm
2
.) Flexible conduit
Flexible or pliable conduits shall not be used as a protective conductor.527-02-02
543-02-01
Conduit fixings
The conduit system has to be selected and erected to minimise any damage occurring to the Category 1, 2 and 3 circuits
sheath and insulation of the conductors during the installation, use and maintenance, of the Category 2 circuits must not be installed in the same conduit as Category 1 circuits, unless the
system. Category 2 circuits are insulated to the highest Category 1 voltage present.
522-08-01
Category 3 circuits must not be installed in the same conduit as Category 1 circuits.
The conduit system has to be so supported that the conductors in the conduit are not exposed to 528-01-04, 528-01-05
undue mechanical strain, and so that there is no undue mechanical strain on the terminations of
the conductors. Consideration shall be given to the conductor’s own weight. Where controls or accessories are mounted in or on a common box, switch plate or block,
category 1 and 2 cables and terminations shall be segregated from each other by a partition. If522-08-04
the partition is metal, it shall be earthed.
Cables that are installed in a vertical conduit shall, where necessary, be provided with additional 528-01-07
support, so that the cables are not damaged by their own weight.
522-08-04 Conduit used for mechanical protection
Short lengths of metal conduit not exceeding 150mm in length which are inaccessible, do not
require protection against indirect contact.Distance between fixings for conduit
471-13-04 (v)
Conduit Maximum distance between supports in metres
Conduit can be used for protecting cables to be installed outdoors on walls, providing it is suitably
size in Metal Plastic Pliable
protected against corrosion.
mm Horizontal Vertical Horizontal Vertical Horizontal Vertical
522-05-01
16 0.75 1.0 0.75 1.0 0.3 0.5
20 1.75 2.0 1.5 1.75 0.4 0.6
Damage during installation
25 1.75 2.0 1.5 1.75 0.4 0.6
The number of cables drawn into a conduit shall be such that no damage occurs to the cable or
32 & 40 2.00 2.25 1.75 2.0 0.6 0.8
conduit during the installation of the cables.
Over 40 2.25 2.5 2.0 2.0 0.8 1.0
522-08
Conduit used as protective conductor
Plain slip or pin grip sockets shall not be used for conduit joints. Joints shall be screwed or made
with substantial mechanical clamps.
543-03-06
Where metal conduit is used as a protective conductor, its cross-sectional area shall be
determined either by application of the formula of 543-01-03, or Table 54G.
543-01-03 formula S mm
2
= √l
2
t
k
Please Note: All prices shown exclude V.A.T.
390
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