Code of Practice for the Electricity (Wiring) Regulations - 2009 Edition

(c) 4 mm 2 PVC insulated copper cables as supplementary bonding
are used to bond the window frames intended to support
air-conditioners.
(B) Example in steps of sizing cable conductors as
described in Code 13A(3)
1. Assumed data
An immersion electric water heater rated at 220V, 2 kW is to be installed
using a 2-core-and-earth PVC-insulated and sheathed, non-armoured
cable. The supply will be taken from an existing 15A spare way in a
consumer’s unit containing semi-enclosed (rewirable) fuses to BS3036.
The supply cable will run for much of its 14 m length in a roof space
which is thermally insulated with glass fibre. The roof space ambient
temperature is expected to be 35°C in summer and, where leaving the
consumer’s unit, the cable will be bunched with seven other 2 core-andearth
cables.
2. Steps in sizing cable conductors
(a) Design current of the circuit
Rated power of the heater 2000
= ———————————– = —— = 9.1A
Supply voltage 220
(b) A 15A semi-enclosed (rewirable) fuse to BS3036 is chosen as the
overcurrent protective device.
(c) Current carrying capacity of the conductors is determined by
applying the following correction factors to the current rating of the
overcurrent protective device (i.e. 15A):
(i) Ambient temperature factor = 0.97
(From Table A5(2) of Appendix 5, using conditions:
Ambient temperature = 35°C
Type of insulation = General purpose PVC)
(ii) Grouping factor = 0.52
(From Table A5(3) of Appendix 5, using conditions:
Number of multicore cable = 8
Reference Method of installation = Bunched and clipped
direct to a non-metallic
surface (Method 1), from
Appendix 7)
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