p388-389:Layout 1 15/5/07 13:04 Page 2
i Technical Information
Trunking as a protective conductor
Cable Management
The cross-sectional area of trunking used as a protective conductor shall be not less than that
given in the formula of Regulation 543-2, or by Table 54G.
TRUNKING
543-01-01
Material Where the trunking is common to several circuits, its cross-sectional area shall be determined by
Trunking shall be manufactured to BS4687. The material of insulated trunking shall have the either of the following criteria:
ignitability characteristic “P” as specified in BS476 Part 5. 1. Using the formula of Regulation 543-01-03, using most unfavourable values of fault current
521-05 and disconnection time for each of the circuits it contains, or
2. Using the conductor with the largest cross-sectional area in Table 54G.
543-01-02
Protection against corrosion
Precautions are to be taken in damp situations against corrosion that can be caused by metal
trunking coming into contact with building materials containing chemicals, of which magnesium
Busbar trunking
chloride, lime, and acidic woods are an example.
When used as a protective conductor, the electrical continuity of enclosed metallic busbar
trunking systems shall be protected against mechanical, chemical, and electrochemical
522-05-01
deterioration, and shall have a cross-sectional area not less than that given either by the formula
Metal trunking and associated fixings exposed to the weather, or installed in damp situations, shall
or by Table 54G, and the enclosure shall allow connection of other protective conductors at every
be made from corrosion resistant material, and shall not be in contact with metals likely to cause
tap-off point.
electrolytic action.
543-02-04
522-05-01, 522-05-02
Category 1,2 and 3 circuits
Entries into trunking shall be so placed or protected that the ingress of water is prevented. When enclosed in the same trunking, Category 1 circuits shall be partitioned from Category 2
(Trunking exposed to the weather shall be of the waterproof type; it is important to make certain circuits, unless the Category 2 circuits are insulated to the highest Category 1 voltage present.
that entries are not made in the top face of the trunking, and that any entry is made waterproof, 528-01-05
by, for example, flanged coupling and lead washer if the entry is for conduit.
522-03-01 Category 3 circuits, when enclosed in the same trunking as other Category circuits, shall be
separated by continuous partitions, unless the Category 1 or Category 2 circuits.
Partitions shall also be installed at any common outlet to the trunking system, which outlet
Heat barriers
Vertical trunking shall be equipped with internal barriers to prevent the air at the top of the trunking
accommodates Category 3 circuits with Category 1 or Category 2 circuits.
becoming excessively hot. As a recommendation, the distance between barriers shall be either
528-01-06, 528-01-07
the distance between floors, or 5 metres whichever distance is least.
Termination of trunking422-01
At the termination of trunking, non-sheathed cables or sheathed cables that have had the outer
sheath removed, shall be enclosed in fire resistant material, unless they are terminated in a box,
Fire barriers
Where trunking passes through walls or floors, the hole round the trunking shall be made good to
accessory or luminaire complying with British Standards.
the same degree of fire resistance as that of the wall or floor. Where the wall or floor has a
designated fire resistance, the trunking shall be internally sealed to maintain the fire resistance of
The building structure may form part of the enclosure referred to above.
the floor or wall. The sealing material shall be compatible with the wiring system, permit thermal
526-03-02, 526-03-03
movement of the cable without reducing the quality of the seal, be removable without damaging
the cables, and have the same degree of resistance to environmental conditions as the wiring Socket outlets
system. The earthing terminal of each socket outlet shall be connected by a separate protective conductor
to an earthing terminal in the trunking, when the socket is mounted in the trunking.527-02
543-02-07
Trunking supports
Trunking shall be so supported, and of such a type, that it is suitable for the risk of the mechanical
CONDUIT
damage which it is likely to incur during normal use. Alternatively, it shall be protected against
Material
such mechanical damage.
Conduit and conduit fittings used should have been manufactured in accordance with British
522-08-04, 522-08-05
Standards:
511-01-01, 521-04
Spacing of supports for trunking
The following table does not apply to lighting suspension trunking, or trunking using special
Corrosion and moisture
strengthening couplers.
Metal conduit and its fixings shall be corrosion-resistant when exposed to the weather, or installed
in damp situations, and must not be in contact with dissimilar metals likely to set up electrolytic
action.
522-05-01
Drainage outlets are to be provided in unsealed conduit systems where moisture may collect, e.g.
through condensation, and protection against mechanical damage shall be provided where it is
subject to waves.
Trunking Maximum distance between supports in metres 522-03-02, 522-03-03
size Metal Insulating
Terminations and junctions
mm x mm Horizontal Vertical Horizontal Vertical
Conduit ends shall be free from burrs. Terminations in equipment not fitted with spout entries shall
16 x 16 0.75 1.00 0.50 0.50
be treated to prevent damage to the cables. (A female bush on the end of the conduit is a suitable
25 x 16 0.75 1.00 0.50 0.50
means of achieving this.)
38 x 16 0.75 1.00 0.50 0.50 522-08-01
38 x 25 1.25 1.50 0.50 0.50
Where cables are connected to a conduit system, substantial boxes with ample capacity shall be
38 x 38 1.25 1.50 0.50 0.50
installed.
50 x 38 1.75 2.00 1.25 1.25 522-08-02
50 x 50 1.75 2.00 1.25 1.25
Every outlet for cables from a conduit system to a duct, or ducting system, shall be so made that
75 x 50 3.00 3.00 1.50 2.00
it is mechanically strong, and cables must not be damaged whilst being installed.
75 x 75 3.00 3.00 1.75 2.00 522-08-01, 522-08-02
Larger sizes 3.00 3.00 1.75 2.00
The termination of conduit, non-sheathed cables, or sheathed cables that have had the outer
sheath removed, shall be enclosed in fire resistant material that complies with British Standards,
unless they are terminated in a box, accessory or luminaire complying with British Standards.
The building - structure may form part of the enclosure referred to above.
526-03-03, 526-03-02
Please Note: All prices shown exclude V.A.T.
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