to the 16th Edition IEE Regulations
   
   
   
 
 

chapter 5
Earthing

chapter 6
Circuits

Cables, conduits and trunking
  4.1 - Cable insulation materials 4.4 - Cable supports, joints and terminations
  4.2 - Cables 4.5 - Cable enclosures
  4.3 - Cable choice 4.6 - Conductor and cable identification
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4.2.1- Non-flexible low voltage cables

Types of cable currently satisfying the Regulations are shown in {Fig 4.1}.

a) Non-armoured pvc-insulated cables - Fig 4.1a

1 - pvc sheath
2 - PVC insulation
3 - copper conductor: solid. stranded or flexible


b) Armoured PVC-insulated cables - Fig 4.1b

1 - PVC sheath
2 - armour-galvanised steel wire
3 - PVC bedding
4 - PVC insulation
5 - copper conductor


c) Split-concentric PVC insulated cables - Fig 4.1c

1 -PVC oversheath 5 - earth continuity conductor:
---- bare copper wires
2 - Melinex binder 6 - PVC phase insulation
3 - PVC strings 7 - copper conductors
4 - neutral conductor:
---- black PVC-covered wires
 


d) Rubber-insulated (elastomeric) cables - Fig 4.1d

1 - textile braided and
---- compounded
2 - 85C rubber insulation
3 - tinned copper conductor


e) Impregnated-paper insulated lead sheathed cables - Fig 4.1e

1 - PVC oversheath 6 -filler
2 - galvanised steel wire armour 7 - screen of metal tape intercalated
---- with paper tape
3 - bedding 8 -impregnated paper insulation
4 - sheath: lead or lead alloy 9 - Carbon paper screen
5 - copper woven fabric tape 10 - shaped stranded conductor


f) Armoured cables with thermosetting insulation - Fig 4.1f

  1 -PVC oversheath
2 -galvanised steel wire armour
3 - taped bedding
4 -XLPE insulation
5 - solid aluminium conductor


g) Mineral-insulated cables Fig 4.1g

1 - LSF oversheath
2 -copper sheath
3 - magnesium oxide insulation
4 - copper conductors


h) Consac cables - Fig 4.1h

1 - extruded PVC or polythene oversheath 4 - paper belt insulation
2 - thin layer of bitumen containing a
---- corrosion inhibitor
5 - paper core insulation
3 - extruded smooth aluminium sheath 6 - solid aluminium conductors


i) Waveconal cables - Fig 4.1i

1 - extruded PVC oversheath
2 - aluminium wires
3 - rubber anti-corrosion bedding
4 - XLPE core insulation
5 - solid aluminium conductors

[Table 52B] gives the maximum conductor operating temperature for the various types of cables. For general purpose p.v.c this is 70C. Cables with thermosetting insulation can be operated with conductor temperatures up to 90C but since the accessories to which they are connected may be unable to tolerate such high temperatures, operation at 70C is much more usual. Other values of interest to the electrician are shown in [ Table 3.7 ]. Minimum cross-sectional areas for cables are shown in [ Table 4.1 ].

Table 4.1 - Minimum permitted cross-sectional areas for cables
(from Table 52C of BS 7671: 1992)
     
type of circuit conductor material cross sectional area (mm)
power and lighting circuits
copper
1.0
(insulated conductors)
aluminium
16.0
signalling and control circuits
copper
0.5
flexibles, more than 7 core
copper
0.1
bare conductors and busbars
copper
10.0
-
aluminium
16.0
bare conductors for signalling and control
copper
4.0

 

 

 

 

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Extracted from The Electricians Guide Fifth Edition
by John Whitfield
Published by EPA Press Click Here to order your Copy

Click here for list of abbreviations