Wiring Enclosures

1
Wiring Enclosures Support(Note All the
mentioned tables in this course refer to, unless
otherwise specified, Low Voltage Electrical
Installation Handbook, by Johnny C.F. Wong,
Edition 2004)

• Chapter 4

2
Protection of cables against Electromechanical
Mechanical Stresses

• Electromechanical forces may be caused by fault
  currents
• Mechanical forces may be caused by accidental
  drilling of holes on a wall, the conduits own
  weight, etc.

3
Conduits

• Rigid Steel Conduits
• Excellent mechanical protection
• Good protection against fire
• Can be used as circuit protective conductor (cpc)
• Resistant to ultra-violet radiation from sunlight
• BS4568-1 classifies conduits by
• Light gauge and heavy gauge (CoP permits only
  heavy gauge conduits)
• Classes 1, 2, 3 4

4
Conduits

• Rigid Insulating Conduits / PVC conduits
• Ambient temperature is a major consideration
• Overall cost saving
• Separate circuit protective conductor must be
  used
• Weight reduction compared with steel conduits

5
Conduits

• Flexible Conduit (Metallic / PVC)
• Used in applications involving constant movement,
  e.g. connection to a pump
• Separate circuit protective conductor must be
  used
• Where exposed to damp situation, it should have
  metallic pattern with PVC oversheath and IP
  rating not less than IP54 (Table 4.16)

6
Conduit

• Supports
• Horizontally surface-mounted
• Vertically surface-mounted
• For rigid steel conduit, refer to Table 4.5
• For rigid insulating conduit, refer to Table 4.7

7
Conduit

• Cable capacity
• - Selection principle Conduit Factor ?
  (Cable Factors)
• Refer to Tables 4.1 to 4.4
• Solid and stranded cables
• Short run (?3m and no bend) and long run (gt3m or
  with bends)
• Adaptable boxes to be installed at least every
  10m straight run.
• Example
• How many 2.5 mm2 1-C PVC cables can be
  accommodated in a 20 mm conduit 10m long
  incorporating 2 bends?

8
Conduit

• Solution
• From Table 4.4, conduit factor for a 20mm
  conduit, 10m long incorporating 2 bends is 141.
• Let the max. no. of cables that can be drawn
  in be x, and from Table 4.3, cable factor for
  2.5mm2 1/C PVC cable is 30, then
• 30x 141 ? x 4.7
• Therefore, we select x 4

9
Trunkings

• Construction
• Steel trunking (screw-on-lid)

10
Trunkings

• PVC (or insulating) trunking (clip-on-lid)

11
Trunkings

• There are other trunking systems also of PVC
  steel construction, e.g. 2- and 3- compartment
  trunkings (telephone and / or data power)-
• Raised floor trunkings (flush with raised floor
  panels)
• Underfloor trunkings
• (flush with floor screed)
• Skirting trunkings

12
Trunkings

• Classification
• The higher the Class, the better the mechanical
  protection, e.g. Class 3 steel trunking ? heavy
  protection on both inside and outside of trunking

13
Trunkings

• Can Be Used as Circuit Protective Conductor (cpc)
• Steel trunkings may be used as cpc, whereas for
  PVC trunkings, separate cpc must be used.

14
Trunkings

• Bends and supports
• Support requirements for steel trunking and
  insulating trunking refer to Tables 4.13 and 4.15

15
Trunkings

• Cable Capacity
• - Selection principle Trunking Factor ?
  (Cable Factors)
• Refer to Tables 4.10, 4.11 and 4.12
• For sizes and types of cable and sizes of
  trunking other than those given in the table, the
  no. of cables drawn into a trunking should be
  45
• Space factor is the percentage occupancy of space
  inside the trunking
• Example
• What is the max. number of 10 mm2 1-C PVC cables
  that can be accommodated in a 100mm x 50mm
  trunking?What if a space factor of 0.45 is
  applied?

16
Cable Supports

• Cable Clips
• For surface-mounted PVC-insulated PVC-sheathed
  non-armoured cables ? 10 mm.sq.

17
Cable Supports

• Cable Cleats / Saddles
• As above but for gt 10 mm.sq. cables and all
  armoured cables.

18
Cable Supports

• Cable Trays and Ladders
• Suitable for almost any mounting method but for
  heavier cables than those accommodated in a
  trunking.
• The mechanical strength of cable ladders is
  better than cable trays.