How to Install Casing Wiring System in a Building?

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Casing wiring is an electrical system wherein PVC insulated wires are placed in a rectangular-shaped plastic casing and covered with a cap. This type of wiring system is also known as wireways.

Casing and capping wiring is considered suitable for indoor wiring works due to aesthetics or technical requirements, such as ease of extension of existing wiring, avoidance of recessed wiring in RCC columns, etc.

PVC-insulated cables and other types of insulated cables should be used in the following ways:

1. The system using PVC wireways shall not be adopted in residential buildings or other locations where there is a risk of tampering. 
2. Restrictions of applications on the use of non-metallic conduits are applicable for PVC casing wiring systems.  
3. Where the casing wiring system has to be necessarily adopted in the abovementioned scenarios, only metallic wireways shall be used.

1. Materials Specification

The standard material specification of casing wiring system are:

1. In extruded sections, the casing and capping shall be of the same material, viz. either PVC or anodized aluminum.
2. The casing shall have a square or rectangular body. 
3. The capping shall be a slide-in type with double grooving in PVC wireways and plain type for metallic wireways.
4.  All surfaces shall have a smooth finish inside and outside.
5.  The top of the sidewalls of the casing body shall be suitable for the above types of fixing arrangement of capping to it. 
6.  PVC casing and capping shall be of good quality PVC, free from defects like deformation, unevenness, blisters, cavities, etc.

2. Dimensional Requirement

The sizes of the casing and capping for the different sizes of cables and the maximum number of PVC insulated aluminum/copper conductor cables that can be carried in one casing are presented size-wise in Table-1. The thickness of the casing and capping shall be 1.2 mm +/- 0.1 mm.

Nominal cross-sectional area of a conductor in sq. mm.	10/15 mm x 10 mm	20 mm x 10 mm	25 mm x 10 mm	30 mm x 10 mm	40 mm x 20 mm	50 mm x 20 mm
1.5	3	5	6	8	12	18
2.5	2	4	5	6	9	15
4	2	3	4	5	8	12
6	-	2	3	4	6	9
10	-	1	2	3	5	8
16	-	-	1	2	4	6
25	-	-	-	1	3	5
35	-	-	-	-	2	4
50	-	-	-	-	1	3
70	-	-	-	-	1	2

3. Installation of Casing Wiring System

3.1 Attachment to Wall and Ceiling

1. The casing shall be fixed using suitable flat head screws to the asbestos or fiber fixing plugs, at intervals not exceeding 60 cm. 
2. On either side of the joints, the distance of the fixing arrangement shall not exceed 15 cm from the joint.
3. The screw head shall be countersunk within the center of the casing. Alternatively, round-headed screws may be used. 
4. All casings shall be fixed directly on the wall or ceiling as above. 
5. The casing shall be used on drywalls and ceiling only and shall not be buried in walls, nor fixed in proximity to gas, steam, or water pipes, or immediately below the latter. 
6. Casing under steel joists shall be secured by MS clips of not less than 1.2 mm (18 SWG) thickness and width not less than 19 mm, or by approved clamps.

3.2 Passing through Floors or Walls

1. When conductors pass through floors, the same shall be carried in an approved PVC conduit or heavy gauge steel conduit properly bushed at both ends.
2. The conduit shall be carried 20 cm above floor level and 2.5 cm below ceiling level and neatly terminated into the casing.
3. Steel conduit pipes wherever accessible shall be securely earthed.

3.3 Joints in Casing and Capping

1. The wireways in straight runs should be in a single piece as far as possible to avoid joints.
2. All joints shall be scarfed or cut diagonally in longitudinal section and shall be smoothed down by filing to make the joints a very close fit as far as possible and without burrs. They shall be screwed at joints with two or more screws as would be necessary.  
3. Joints in capping shall not overlap those in the casing. 
4. Joints arising out of bends or diversions shall be carried out using standard accessories like elbows, tees, 3-way/4-way junctions, etc., of high-grade PVC/aluminum alloy.
5. In no case, the radius of curvature of the cables inside a bend shall be less than six times their overall diameter.

3.4 Attachment of Capping

1. Wherever required, capping shall not be fixed until the work has been inspected with the wires in position and approved.
2. Capping shall be attached to the casing in individual sections only after the insulated wires are laid inside. 
3. No screws or nails shall be used for fixing PVC capping to the casing.
4. Metallic capping shall be fixed using cadmium plated flat head/round head screws in a staggered manner with an axial spacing not exceeding 30 cm.

3.5 Installation of Cables 

1. For ease of maintenance, cables carrying direct current or alternating current shall always be bunched so that the outgoing and returning cables are drawn in the same casing. 
2. Necessary clamps shall be provided to hold the wires inside the casing at suitable intervals so that at the time of opening of the capping, the wires may remain in position in the casing and do not fall out.

3.6 Earth Continuity 

1. A protective conductor shall be drawn inside the casing and capping for earthing of all metallic boxes of the installations and connections to the earth pin of the socket outlets. 
2. In metallic casing and capping, there shall be a metallic link between adjacent casings with screw connections and connections from the end casing to the earth terminal of metallic boxes/outlets/switchboards for complete body earthing of the system.

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