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 - 85°C 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 70°C. Cables with thermosetting insulation can be operated with conductor temperatures up to 90°C but since the accessories to which they are connected may be unable to tolerate such high temperatures, operation at 70°C 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 (mm²)
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