14A General Requirements
(1) Enclosures as protective conductors (2) Support of enclosures
(3) Fire barrier 14BSteel Conduit System
(1) Construction (2) Installation 14C Steel Trunking System
(1) Construction (2) Installation
14D Plastic or PVC Conduit or Trunking (1) Construction
(2) Installation
14E Cable Capacity of Enclosures (1) General requirements
(2) Determination of cable capacities 14F Enclosures of Busbar Trunking System 14G Workmanship
Code 14 WIRING INSTALLATION ENCLOSURE
14A General Requirements
(1) Enclosures as protective conductors
(a) Metallic enclosures for cables, busbar trunking and switchgear and controlgear assemblies, where used as protective conductors should:
(i) have a cross-sectional area not less than that determined from the application of Code 11C(2)(e) or verified by test in accordance with IEC 60439-1 or equivalent;
(ii) have an electrical continuity achieved and maintained to afford protection against mechanical, chemical or electrochemical deterioration; and
(iii) permit the connection of other protective conductors at every predetermined tap-off point.
(b) Where conduit, trunking or ducting are used as a protective conductor, the earthing terminal of each accessory should be connected by a separate protective conductor of adequate size to an earthing terminal incorporated in the associated box or enclosure.
(2) Support of enclosures
All conduit, ducting and trunking installations should be properly supported and of a type suitable for any risk of mechanical damage to which they may be liable in normal conditions of service or adequately protected against such damage.
(3) Fire barrier
(a) Where conduit, duct, ducting or trunking pass through fire-resistant structural elements such as floors and walls designated as fire barriers, the opening made should be sealed according to the appropriate degree of fire resistance.
(b) Where cables, conduits or conductors are installed in channel, duct, ducting, trunking or shaft which pass through fire-resistant structural elements, suitable internal fire-resistant barriers should be provided to prevent the spread of fire.
14B Steel Conduit System (1) Construction
(a) Steel conduits and fitting with metric thread, except flexible conduits, should be of heavy gauge, longitudinally welded type and comply with BS4568, BS EN 60423, BS EN 50086, IEC 60423, IEC 60614-1 or equivalent. The nominal minimum outside diameter of any rigid conduit to be used should be 16 mm with a minimum wall thickness of 1.4 mm.
(b) Flexible steel conduits should comply with IEC 60614-2-5 or BS731:
Part 1 or equivalent. In addition, where flexible conduits are exposed to weather or in damp situations, the conduits should be of the metallic type with PVC oversheath.
(c) All steel conduits, conduit fittings and the associated metallic boxes for the enclosure of electrical accessories should be protected against corrosion on both the inside and outside surfaces.
(2) Installation
(a) The steel conduit installation should be made mechanically and electrically continuous throughout, be effectively earthed and comply with BS4568, BS EN 60423, BS EN 50086, IEC 60423, IEC 60614-1 or equivalent.
(b) An adequate number of suitably sized adaptable boxes should be provided in the conduit installation to enable cables to be drawn in easily and without damage.
(c) Flexible steel conduit should not be used as a protective conductor and it should have a separate circuit protective conductor of adequate size for earth continuity.
(d ) Conduits should be installed so as to prevent accumulation of condensed moisture or water in any part of the installations.
14C Steel Trunking System (1) Construction
(a) Steel trunking and fittings should be fabricated with sheet steel having a minimum thickness as indicated in Table 14(1) and should comply with the requirements specified in BS4678: Part 1 or equivalent.
(b) Underfloor trunking should be compatible to the requirements laid down in BS4678: Part 2 or equivalent and should be fabricated with sheet steel of:
(i) not less than 1.2 mm thickness for compartment width up to and including 100 mm;
(ii) not less than 1.6 mm thickness for compartment width over 100 mm; and
(iii) not less than 1.0 mm thickness for the partitions and connector material.
(c) Steel trunking installations should be constructed using manu-facturer’s standard fittings such as tee or angle pieces, connectors etc., throughout as far as practicable.
(d ) All steel trunking and fittings should be protected against corrosion.
(2) Installation
(a) The steel trunking installation should be made mechanically and electrically continuous throughout, and be effectively earthed.
(b) Electrical continuity should be achieved by means of connecting a protective conductor (e.g. copper tape) of adequate size across the two adjacent ends of the trunking.
(c) Every entry to the trunking installation should be so placed as to prevent and/or to be protected against the ingress of water.
14D Plastic or PVC Conduit or Trunking (1) Construction
(a) Rigid plastic or PVC conduits and conduit fittings should be of such strength to withstand the stress under the installed conditions. They should comply with BS4607: Part 1 and 2 and IEC 60614 or BS EN 50086 or equivalent.
(b) Pliable conduits should be made of self-extinguishing plastic material and comply with BS4607: Part 3 or equivalent.
(c) Adaptable boxes and boxes for the enclosure of electrical accessories that are made of insulating materials should comply with BS4662 or equivalent and have a minimum wall thickness of 2 mm.
(2) Installation
(a) Plastic or PVC conduit or trunking systems should only be installed where they are suitable for the extremes of ambient temperature to which they are likely to be subject under the installed conditions.
Rigid PVC conduits or trunking should not be used where the normal working temperature of the installation may exceed 60°C.
(b) Any exposed conductive parts of a PVC or plastic conduit system or trunking should be connected to earth by protective conductor of adequate size for maintaining an effective continuity. Where the plastic or PVC conduit system is made between metal conduit system, the earthing connection should be made at the steel conduit/trunking and at the nearest boxes with proper terminals.
(c) The method of support and installation for rigid PVC conduits should allow for the longitudinal expansion and contraction of the conduits which may occur with variation of temperature under normal operating conditions.
14E Cable Capacity of Enclosures
Cable capacities of conduit and trunking enclosing single-core PVC insulated cables can be determined by the ‘unit system’ method described below:
(a) Straight runs of conduit not exceeding 3 m in length:
(i) For each cable to used, obtain the appropriate cable factor from Table 14(2)(a).
(ii) Add all the cable factors so obtained and compare with the conduit factors given in Table 14(2)(b).
(iii) The conduit size is considered satisfactory if the conduit factor is equal to or exceeds the sum of the cable factors.
(b) Straight runs of conduit exceeding 3 m in length or in runs of any the length of run and number of bends in that run.
(iii) The conduit size is considered satisfactory if the conduit factor is equal to or exceeds the sum of the cable factors.
(iv) The term ‘bend’ signifies a 90° bend and one double set is equivalent to one bend.
(c) Trunking of any length of run:
(i) For each cables to be used, obtain the appropriate cable factor from Table 14(4)(a).
(ii) Add all the cable factors so obtain and compare with the trunking factors given in Table 14(4)(b).
(iii) The trunking size is considered satisfactory if the trunking factor is equal to or exceeds the sum of the cable factors.
(d ) For sizes and types of cable and sizes of trunking other than those given in Tables 14(4)(a) and 14(4)(b), the number of cables drawn into a trunking should be such that the resulting space factor should not exceed 45%.
(Note: Space factor is defined as the ratio (expressed as a percentage)of the sum of the overall cross-sectional area of cables (including insulation and any sheath) to the internal cross-sectional area of the trunking in which they are
installed. The effective overall cross-sectional area of a non-circular cable is taken as that of a circle of diameter equal to the major axis of the cable.)
14F Enclosures of Busbar Trunking System
Requirements for the enclosures of busbar trunking system are described in Code 26B.
14G Workmanship
(a) Conduits should not be bent in such a manner which appreciably distorts their original cross-sectional shape or causes damage to the conduits.
(b) Burrs, sharp edges and projections should be removed from the internal surfaces and ends of conduits, trunking or other enclosures when installed.
(c) Where the protective coating on a metallic enclosure has been damaged after installation, such surface should be effectively restored by paint or other suitable coating to prevent corrosion.
(d ) Other details relating to the workmanship of installation of conduits and trunking are described in Code 25.
Table 14(1)
Minimum Thickness of Body Material for Metallic Trunking
(Note: Metallic trunkings having nominal size differing from the table but complying with IEC 61084 or equivalent are also acceptable.)
Nominal Size Minimum Thickness of Body
(mm ×mm) Material (in mm)
050 ×500 1.0
075 ×500 1.2
075 ×750 1.2
100 ×750 1.2
150 ×100 1.4
150 ×150 1.6
Table 14(2)
Cable Factors and Conduit Factors for Straight Runs of Conduit not Exceeding 3 m in Length
(a) Cable Factor
(b) Conduit Factor Conduit Diameter
(mm) Factor
16 290
20 460
25 800
32 1 400
Conductor Cross-Sectional
Type of Conductor Area (mm2) Factor
1 22
Solid 111.5 27
112.5 39
111.5 31
112.5 43
Stranded 4 58
6 88
10 146
Table 14(3)
Cable Factors and Conduit Factors for Conduit Exceeding 3 m in length or in Runs Incorporating Bends or Sets
(a) Cable Factor
(b) Conduit Factor Conductor Cross-Sectional
Type of Conductor Area (mm2) Factor
1.0 16
1.5 22
2.5 30
Solid or stranded
40. 43
60. 58
10. 105
Conduit Diameter (mm) Length of
Run (m)
Straight One bend Two bends Three bends Four bends
1 188 303 543 947 177 286 514 900 158 256 463 818 130 213 388 692
1.5 182 294 528 923 167 270 487 857 143 233 422 750 111 182 333 600
2 177 286 514 900 158 256 463 818 130 213 388 692 97 159 292 529
2.5 171 278 500 878 150 244 442 783 120 196 358 643 86 141 260 474
3 167 270 487 857 143 233 422 750 111 182 333 600
3.5 179 290 521 911 162 263 475 837 136 222 404 720 103 169 311 563 4 177 286 514 900 158 256 463 818 130 213 388 692 97 159 292 529 4.5 174 282 507 889 154 250 452 800 125 204 373 667 91 149 275 500 5 171 278 500 878 150 244 442 783 120 196 358 643 86 141 260 474 6 167 270 487 857 143 233 422 750 111 182 333 600
7 162 263 475 837 136 222 404 720 103 169 311 563 8 158 256 463 818 130 213 388 692 97 159 292 529 9 154 250 452 800 125 204 373 667 91 149 275 500 10 150 244 442 783 120 196 358 643 86 141 260 474
16 20 25 32 16 20 25 32 16 20 25 32 16 20 25 32 16 20 25 32
Covered by Tables 14(2) (a) and (b)
Table 14(4)
Cable Factors and Trunking Factors for Trunking of any Length of Run (a) Cable Factor
(b) Trunking factor Conductor Cross-sectional
Type of Conductor Area (mm2) Factor
Solid 111.5 7.1
112.5 10.2
111.5 8.1
112.5 11.4
Stranded 4 15.2
6 22.9
10 36.3
Dimensions of trunking
(mm ×mm) Factor
00050 ×37.5 767
050 ×50 1 037
075 ×25 738
0075 ×37.5 1 146
075 ×50 1 555
075 ×75 2 371
100 ×25 993
0100 ×37.5 1 542
100 ×50 2 091
100 ×75 3 189
0100 ×100 4 252