Technical Support - Cable Management
TRUNKING
Material
Trunking shall be manufactured to BS4687. The material of insulated trunking shall have the ignitability characteristic "P"as specified in BS476 Part 5.
521-05
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 chloride, lime, and acidic woods are an example.
522-05-01
Metal trunking and associated fixings exposed to the weather, or installed in damp situations, shall be made from corrosion resistant material,and shall not be in contact with metals likely to cause electrolytic action.
522-05-01, 522-05-02
Entries into trunking shall be so placed or protected that the ingress of water is prevented. (Trunking exposed to the weather shall be of the waterproof type;it is important to make certain that entries are not made in the top face of the trunking,and that any entry is made waterproof, by, for example, flanged coupling and lead washer if the entry is for conduit.
522-03-01
Heat barriers
Vertical trunking shall be equipped with internal barriers to prevent the air at the top of the trunking becoming excessively hot. As a recommendation, the distance between barriers shall be either the distance between floors, or 5 metres whichever distance is least.
422-01
Fire barriers
Where trunking passes through walls or floors, the hole round the trunking shall be made good to 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 floor or wall. The sealing material shall be compatible with the wiring system, permit thermal 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 system.
527-02
Trunking supports
Trunking shall be so supported, and of such a type, that it is suitable for the risk of the mechanical damage which it is likely to incur during normal use. Alternatively, it shall be protected against such mechanical damage.
522-08-04, 522-08-05
Spacing of supports for trunking
The following table does not apply to lighting suspension trunking,or trunking using special strengthening couplers.
Click here to view table.
Trunking as a protective conductor
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.
543-01-01
Where the trunking is common to several circuits, its cross-sectional area shall be determined by either of the following criteria:
1) Using the formula of Regulation 543-01-03,using most unfavourable values of fault current 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
Busbar trunking
When used as a protective conductor, the electrical continuity of enclosed metallic busbar trunking systems shall be protected against mechanical, chemical, and electrochemical deterioration, and shall have a cross-sectional area not less than that given either by the formula or by Table 54G, and the enclosure shall allow connection of other protective conductors at every tap-off point.
543-02-04
Category 1,2 and 3 circuits
When enclosed in the same trunking,Category 1 circuits shall be partitioned from Category 2 circuits, unless the Category 2 circuits are insulated to the highest Category 1 voltage present.
528-01-05
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 accommodates Category 3 circuits with Category 1 or Category 2 circuits.
528-01-06, 528-01-07
Termination of trunking
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,accessory or luminaire complying with British Standards.
The building structure may form part of the enclosure referred to above.
526-03-02,526-03-03
Socket outlets
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.
543-02-07
CONDUIT
Material
Conduit and conduit fittings used should have been manufactured in accordance with British Standards:
511-01-01, 521-04
Corrosion and moisture
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.
522-03-02, 522-03-03
Terminations and junctions
Conduit ends shall be free from burrs. Terminations in equipment not fitted with spout entries shall be treated to prevent damage to the cables. (A female bush on the end of the conduit is a suitable means of achieving this.)
522-08-01
Where cables are connected to a conduit system,substantial boxes with ample capacity shall be installed.
522-08-02
Every outlet for cables from a conduit system to a duct,or ducting system,shall be so made that it is mechanically strong,and cables must not be damaged whilst being installed.
522-08-01, 522-08-02
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
Ambient temperature
Conduits shall be suitable for the maximum and minimum values of ambient temperature to which they will be exposed in normal service.
Where non-metallic or plastic boxes are in contact with a luminaire, they shall be suitable for the suspended load,and the temperature to which they will be subjected.
522-01-01
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.
522-12-01
Colour code
Where conduit is to be distinguished from other services, it shall be coloured orange.
514-02
Prefabricated systems
Where conduit systems are prefabricated and not wired in situ, allowance shall be made for tolerances in the building dimensions. Precautions against damage to such systems shall be taken,so that the conduits or cable ends are not damaged during erection,or during building operations.
522-06-01, 522-08,522-12-01
Fire barriers
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 which it is passing.
527-02-01
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 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 the conduit system has a maximum internal cross-sectional area of 710mm 2 , and is a non-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 .)
527-02-02
Conduit fixings
The conduit system has to be selected and erected to minimise any damage occurring to the sheath and insulation of the conductors during the installation,use and maintenance, of the system.
522-08-01
The conduit system has to be so supported that the conductors in the conduit are not exposed to 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.
522-08-04
Cables that are installed in a vertical conduit shall, where necessary, be provided with additional support,so that the cables are not damaged by their own weight.
522-08-04
Click here to view figures.
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.
546-02-05
Where a conduit is used as a protective conductor, its electrical continuity has to be assured, and has to be protected against mechanical, chemical or electrochemical deterioration.
543-02-05, 543-02-04
Where a conduit is used as the circuit protective conductor for more than one circuit, it shall be sized either by;
1) calculation,using the formula 543-01-03 and the most onerous value of fault current and disconnection time encountered in each of the various circuits, or
2) selected by using Table 54G, with the cross-sectional area of the largest cable enclosed in the conduit.
543-01-02
When conduit is used as a protective conductor, it shall be protected against mechanical, chemical and electrodynamic effects.
543-03-01
The joints in conduit when used as a circuit protective conductor do not need to be accessible.
543-03-03
Conduit shall not be used as a PEN conductor.
546-02-07, 543-02-10
Where a protective conductor is used for both protective and functional purposes, the requirements for the protective measures shall prevail.
546-01
Flexible conduit
Flexible or pliable conduits shall not be used as a protective conductor.
543-02-01
Category 1,2 and 3 circuits
Category 2 circuits must not be installed in the same conduit as Category 1 circuits, unless the Category 2 circuits are insulated to the highest Category 1 voltage present.
Category 3 circuits must not be installed in the same conduit as Category 1 circuits.
528-01-04, 528-01-05
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. If the partition is metal, it shall be earthed.
528-01-07
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.
471-13-04 (v)
Conduit can be used for protecting cables to be installed outdoors on walls, providing it is suitably protected against corrosion.
522-05-01
Damage during installation
The number of cables drawn into a conduit shall be such that no damage occurs to the cable or conduit during the installation of the cables.
522-08
Click here to view figures.
Conduit Installation and Capacity Notes - Plastic
Centaur conduit is light in weight (16% of weight of steel conduit),is clean and easy to handle, does not require the use of on-site special equipment such as vice bender or thread cutting gear, is non-conductive, will not corrode or stain plaster.
Oval conduit and high impact channel are usually used for short runs in domestic situations for external fixing or where the deep chasing required for round conduit is not possible.
uPVC conduit has a rate of expansion greater than that of steel;it is therefore important to make sure that surface work allows for a sliding joint into boxes or couplings, this will permit movement along the conduit run and avoid distortion.
The distance between saddles or slips should not exceed 4"Oç (1.20m). If possible the boxes should be fixed first and a line used to establish correct alignment, which will ease the threading of cable through the conduit. Cutting can be performed with any fine-toothed saw.
Bending or forming of conduit of 25mm dia. or less can be achieved cold provided the appropriate bending spring is employed internally in the location of the bend. Greater diameters may need local application of gentle heat. Cable is threaded by using the Centaur draw tape illustrated on this page.
Centaur plastic conduit cement provides a waterproof permanent joint which is easily made by painting the female internal surface of any joint before sliding the male section in with a twisting action to spread the cement evenly.
Centaur conduit Cable Capacity
Calculation system based on Appendix 12 IEE Regulations - 16th Edition.
1) For each cable it is intended to use, obtain the cable factor from tables 12A or 12C.
2) Add the cable factors thus obtained and compare with the conduit factor (tables 12B or 12D).
3) The appropriate conduit size is the one having a factor equal to or greater than the sum of the cable factors.
Click here to view figures
Single-core pvc insulated cables in straight runs of conduit exceeding 3m in length or in runs of any length incorporating bends or sets. Centaur can accept no liability for the above tables which are given only for guidance purposes.
|
