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Page 1



DOMESTIC WIRING

THE INSTITUTION OF ENGINEERS
SRI LANKA

MAY 2009

Technical Information Series Publication
No: TIS001, Edition 1

Page 2



THE INSTITUTION OF ENGINEERS
SRI LANKA

Technical Information Series Publication No: TIS001,
Edition 1

DOMESTIC WIRING
MAY 2009

Sponsored by:

LANKA ELECTRICITY COMPANY (PRIVATE) LIMITED
411,Galle Road

Colombo 3.

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Conductor size

The minimum size of the conductor in the circuits and non-fused
spurs is given in Table 7. However, if the cables of more than two circuits
are bunched together or ambient temperature exceeds 300C, the size of
the conductor is increased and is determined by applying the appropriate
correction factors from Table 8, so that the conductor size is then corresponds
to a current-carrying capacity not less than:
i. 20A for circuit A1
ii. 30A or 32A for circuit A2
iii. 20A for circuit A3
The conductor size of a fused spur is determined from the total
current demand served by that spur, which is limited to a 13A.
iv. when such a spur serves socket-outlets the minimum conductor
size is 1.5 mm2 for pvc insulated cables with copper conductors

Cooker circuits in household premises

The circuit supplies a control switch or a cooker unit which
incorporates a socket-outlet.

The rating of the circuit is determined by the assessment of the
current demand of the cooking appliance(s) and control unit socket-outlet if
any, in accordance with Table 6.

A circuit of rating exceeding 15A but not exceeding 50A may supply
two or more cooking appliances where these are installed in one room. The
control switch should be placed within two metres of the appliance. Where
two stationary appliances are installed in one room, one switch may be used
to control both appliances provided that neither appliance is more than two
metres from the switch.

Correction factors for current carrying capacity

The current-carrying capacity of a cable for continuous service is
affected by ambient temperature, by grouping and by enclosing in a thermal
insulation material. The cables are rated for 30oC and domestic wiring in Sri
Lanka is unlikely to exceed this temperature. Enclosing in a thermal insulation
would also be a rare occurrence. The correction factors for grouping are given
in Table 8.

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(Source: Table 4B1, Appendix 4, 16th Edition of IEE Regulations)

Method of
Installation

TABLE 8. Correction factors for groups of more than one circuit

Correction factor

Number of circuits

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Single core cables
in conduit or
trunking on a wall
or ceiling

Single layer
clipped to a non-
metallic surface
(Touching)

Single layer
clipped to a non-
metallic surface
(Spaced)

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References:

1. “Regulations for the Electrical Equipment of Buildings”, 14th
Edition, Reprinted in Metric Units Incorporating Amendments,
The Institution of Electrical Engineers, 1970

2. “Regulations for Electrical Installations”, 15th Edition, The
Institution of Electrical Engineers, 1981

3. BS 7671:1992 “Requirements for Electrical Installations, IEE
Wiring Regulations”, 16th Edition, BSI and The Institution of
Electrical Engineers, 1992

4. BS 7671:2001(2004) “Requirements for Electrical Installations,
IEE Wiring Regulations”, 16th Edition, Reprinted incorporated
amendments up to 2004 BSI and The Institution of Electrical
Engineers, 2004

5. K. A. Miller, “Guide to the IEE Wiring Regulations”, Second
Edition, Peter Peregrinus Ltd., 1970

Regulations”, 3rd impression with minor corrections, Peter
Peregrinus Ltd.(on the behalf of IEE), 1982

7. “On-Site Guide to the 16th Edition Wiring Regulations”, The
Institution of Electrical Engineers, 1992

8. “The Crabtree Electrical Handbook”, 4th Edition, J. A. Crabtree
& Co. Ltd., 1968

9. J. O. Paddock and R. A. W. Galvin, “Electrical Installation,
Technology and Practice”, ELBS Edition, English Universities
Press, 1970

10. W.E.Steward, “Modern Wiring practice”, 7th (Metric) Edition,
Newnes-Butterworths, 1971

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