This is the most common cable used for domestic wiring today. PVC-sheathed T&E cable

• Live and neutral are individually insulated, and the Circuit Protective Conductor (CPC) (aka earth) is bare
• There is an overall sheath of grey PVC (BS 6004), or white for low smoke compound (BS 7211)
• Not suitable for unprotected use outside (outer sheath materials are vulnerable to attack by UV radiation)
• 1mm² 1.5mm² & 2.5mm² have solid (non-stranded) conductors
• 4mm², 6mm², 10mm², 16mm² and higher have stranded conductors

Cable Sizes

Conductor area / CPC area (mm²)	Current carrying capacity (A) for various reference methods (see table below)							Conductor dia (mm)	Outer PVC size (h x w)(mm)
	A	B	C	100	101	102	103
1 / 1	11.5	13	16	13	10.5	13	8	1 x 1.13	4.5 x 8.2
1.5 / 1	14.5	16.5	20	16	13	16	10	1 x 1.38	4.7 x 8.2
2.5 / 1.5	20	23	27	21	17	21	13.5	1 x 1.78	5.3 x 9.9
4 / 1.5	26	30	37	27	22	27	17.5	7 x 0.85	6.1 x 11.4
6 / 2.5	32	38	47	34	27	35	23.5	7 x 1.04	6.8 x 13.1
10 / 4	44	52	64	45	36	47	32	7 x 1.35	8.4 x 16.8
16 / 6	57	69	85	57	46	63	42.5	7x 1.71	9.6 x 19.5

 
Installation Methods
The current carrying capacity of any cable is dictated by its maximum conductor temperature, and this in turn will be affected by its ability to dissipate heat. The way it is installed can have a significant effect on this ability. The following table explains the methods cited above. The number of installation methods described in Table 4A2 (previously 4A1) has risen from 20 to 50-odd. Although this may appear to make things more complicated, the appendix now embraces installation methods that are used but which were not previously accounted for, including installation methods in building voids, direct in ground, in ducts in the ground, and flat twin and earth cables in thermal insulation. It is impractical to calculate and publish current ratings for every installation method, since many would result in the same current rating. Therefore a suitable (limited) number of current ratings have been calculated which cover all of the installations stated in the Wiring Regulations, and are called reference methods. All the individually numbered installation methods have a lettered reference method stated against them in Table 4A2, except for flat twin and earth cables which have reference method numbers 100 to 103. There are seven alphabetically lettered reference methods, that is A to G.

BS7671 17th Editon Reference Method	Example of installation method	BS7671 16th Edtn Reference method	BS7671 17th Edtn Installation method
A	In conduit in an insulated wall with the conduit close to or touching the inner skin.	methods 4 & 6	methods 1 & 2
B	Enclosed in conduit or trunking on or in a wall.Â	method 3	methods 4 & 5
C	Clipped direct, or sheathed cables embedded directly in masonry, brickwork, concrete, plaster or the like (other than thermally insulating materials)	method 1	method 20
100	Above a plasterboard ceiling covered by thermal insulation, insulation thickness <100 mm.Â	15	method 100
101	As above but with insulation thickness >100 mm.Â	15	method 101
102	In a stud wall with thermal insulation with the cable touching the innerwallsurface.	15	method 102
103	In a stud wall with thermal insulation with the cable NOT touching the inner wallsurface.	15	method 103

 

• Methods 100, 101 and 102 require the cable to be in contact with the plasterboard ceiling, wall or joist
• Ratings (BS 7671 Table 4D5A (16th), or Table 4D5 (17th)) apply for ambient temperature of 30 deg.C and a maximum conductor temperature of 70 deg.C
• All the usual derating factors apply (see below and appendix 4 of BS 7671 or appendix 6 of the OSG).
• Current ratings are continuous.
• Outer cable sizes are guideline figures and can vary for different brands of cable of the same conductor size.

Reference methods not included in the table are.

• Reference method D – Direct in the ground or in ducting in the ground.
• Reference method E – Multicore cables in free air or on perforated trays.
• Reference method F – Single-core cable touching in free air or on perforated trays.
• Reference method G – Single-core cable spaced in free air or on perforated trays.

T&E current carrying capacity
Note The current carrying capacity values given for the various cable sizes above are only correct for the fixing methods listed. They are also only correct for a single cable not in close proximity to any other cables. For all other installation methods not covered above, the values stated will be incorrect. To find the correct rating in these circumstances the quoted current carrying capacity listed in columns C (i.e. method 1) will need to be “de-rated”. This means that correction factors need to be applied to the current carrying capacity in order to factor out these environmental effects that otherwise could result in cable overheating (and hence overloading) if ignored. In addition to the fixing method, there are other correction factors that will effect the rating:

• Ambient Temperature
• Covering in thermal insulation
• Grouping cables together
• Use of semi enclosed (rewireable) fuses
• Encapsulation in conduit or trunking

For full details of the de-rating factors and more detailed version of current carrying capacity table, see table 4D1A in appendix 6 of the On Site Guide.

Typical T&E Cable Applications

Cable Size (mm²)	Typical Applications
1.0	lighting circuits
1.5	high power lighting circuits, 16A Radial power circuits
2.5	32A Ring final circuits, 20A Radial circuits
4.0	32A Radial circuits, Cooker circuits, low power electric showers
6.0	Small Sub mains, Radial circuits for showers, high power cookers, and other high power devices
10.0	Sub Mains, Radial circuits for high power showers, cookers, and other very high power devices
16.0	Sub Mains