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*Max Cable Load referes to the maximum allowable current for the cable used in the configuration given above and will vary considerably under different configurations.

Caution - for Guidance ONLY
NO guarantee as to the accuracy of these values is given.
And they should be checked against some other source.

Cable Types:

  • Twin & Earth or Three Core & Earth
    House wiring cable
    Conductor temperature 70°C
  • S.W.A XLPE ( TLC - Standard SWA )
    SWA with XLPE thermosetting insulation giving an increased current carrying capacity.
    Conductor temperature 90°C
  • S.W.A PVC
    S.W.A with standard PVC insulation.
    Conductor temperature 70°C
  • Hituf
    PVC insulated with Tough PVC thermosetting insulation giving an increased current carrying capacity.
    Suitable for building sites and some garden and other tough conditions.
    Conductor temperature 70°C

Applications

  • Method 100 - Above a plasterboard ceiling with less than 100mm insulation
    Installation methods for flat twin and earth cable clipped direct to a wooden joist above a plasterboard ceiling with a minimum U value of 0.1W/m K and with thermal insulation not exceeding 100 mm in thickness
  • Method 101 - Above a plasterboard ceiling with more than 100mm insulation
    Installation methods for flat twin and earth cable clipped direct to a wooden joist above a plasterboard ceiling with a minimum U value of 0.1 W/m K and with thermal insulation exceeding 100 mm in thickness
  • Method 102 - In an insulated stud wall with the cable touching the plasterboard
    Installation methods for flat twin and earth cable in a stud wall with thermal insulation with a minimum U value of 0.1 W/m K with the cable touching the inner wall surface
  • Method 103 - In an insulated stud wall with the cable NOT touching the plasterboard
    Installation methods for flat twin and earth cable in a stud wall with thermal insulation with a minimum U value of 0.1 W/m K with the cable not touching the inner wall surface
  • In conduit in an insulated wall (including Thermalite)
  • Clipped direct to a wall
Wherever practical, a cable is to be fixed in a position such that it will not be covered with thermal insulation

Notes:

  • When cables are grouped or bunched, any cables carrying less than 30% of the load may be ignored for the purpose of obtaining the rating for the rest of the group.
  • Where accurate calculations are required please refer to the IEE 17th Edition regulations.

Examples

An immersion heater rated at 240 V, 3 kW is to be installed using twin and earth cable. The circuit will be fed from a 16A MCB over 14m in a roof space which is insulated with glass fibre.The roof space temperature is expected to rise to 50°C in summer.

A. Where it leaves the consumer unit and passes through a 50 mm insulation-filled cavity,the cable will be bunched with seven others.
Required Cable Size: 10mm
This adds considerably to the costs and would make it difficult to terminate such a large cable in the accessories. A more sensible option would be to look for a method of reducing the required cable size.

B. Eight cables leave the consumer unit in two bunches of four
Result: 6mm

D. To attempt to make the cable size smaller, if the eight cables left the consumer unit in four bunches of two
Result: 4mm

C. If it were possible to run the cable out on its own then no grouping factor would apply.
Result: 2.5mm

E. Finally, if the cable left the consumer unit on its own and the cable was not in contact with the glass fibre and clipped direct to the rafters in the loft space.
Result: 1.5mm