p380-381:Layout 1 15/5/07 13:05 Page 1
i Technical Information
BS 4343 16A socket outlets
Wiring Accessories
The requirements can be summarised in a list:
1 the circuit shall be a radial circuit,
2 the protective device for the circuit shall be 20A, and the maximum demand for the circuit,
BS1363 13a socket outlets must not exceed 20A,
General Requirements 3 the number of socket outlets is unlimited,
4 the circuit conductor size is determined in the same way as for other circuits, the conductor
A ring or radial circuit, with or without spurs, can feed an unlimited number of socket outlets, or size being obtained from the tables in Appendix 9, after derating factors for grouping,
feed permanently connected equipment, providing any immersion heater fitted to a storage vessel ambient temperature, contact with thermal insulation, and the type of protective device used,
having the capacity exceeding 15litres, or permanently connected heating appliances used as part if applicable, have been taken into account,
of a space heating installation, are supplied from their own separate circuits. 5 the current-carrying capacity of the cable shall be not less than the nominal rating of the
overcurrent protective device protecting the circuit,
The area covered by a circuit shall be determined by the known or estimated load which must not 6 the current rating of socket outlets used shall be 16A, and of a type appropriate to the
exceed the nominal rating of the circuit protective device, and the floor area covered shall not number of phases, circuit voltage, and earthing arrangement applicable.
exceed the area given in Table 1
The number of socket outlets shall be such that every portable luminaire and appliance can be fed BS 196 Industrial socket outlets
from an adjacent and conveniently accessible socket outlet. The circuit can be a radial circuit or a ring circuit with spurs.
INF, 553-01-07
The number of socket outlets is unlimited.
TABLE 1 The protective device shall not have a nominal rating exceeding 32A; and the maximum demand
for the circuit after diversity has been taken into account must not exceed the nominal rating of
Cable sizes and maximum floor area allowed
the protective device or 32A.
for BS1363 socket outlet circuits
Type of Overcurrent device Minimum conductor Maximum
No diversity is to be allowed for permanently connected equipment; such equipment must be
assumed to be working continuously.
circuit allowed size in mm
2
floor area in
Rating Type PVC MICC square metres
The total current taken by a fused spur must not exceed 16A.
Ring 30/32A Any 2.5 1.5 100
Cartridge
The circuit conductor size is determined in the following manner:
Radial 30/32A fuse or 4 2.5 50
circuit
For radial circuits: l
t
=
l
n
breaker
G x A x T
Radial 20A Any 2.5 1.5 20
Where: l
n
is the rating of the circuit protective device,
G is the correction factor for grouping,
Table 1 already takes into account diversity within the circuit, so no further diversity shall be
A is the correction factor for ambient temperature.
applied. Where more than one final ring circuit is installed the load shall be distributed among
l
t
is the calculated current-carrying capacity required for the cables
them.
For ring circuits: l
t
=
l
n
x 0.67
The cable sizes given in Table 1 may need to be increased if the ambient temperature is likely to G x A x T
exceed 30°C, if more than two circuits are bunched or grouped together.
The current-carrying capacity for the conductors of a spur off the ring is determined by the total
Determination of cable sizes
load on the spur which must not exceed 16A.
When more than two ring circuits are grouped together, or when the ambient temperature exceeds
30°C, or when the conductor is totally enclosed in thermal insulation, the cable size required has
Non-fused spurs are not allowed; a fused spur is to be connected to the ring circuit through a
to be calculated. The cable size is determined by calculating the current-carrying capacity
fused connection unit; the rating of the fuse in the fused spur not exceeding 16A, or the current-
required for the conductors from the following formula:
carrying capacity of the cable for the spur after correction factors (if applicable) have been applied.
I
t
= l
n
x 0. 67
Permanently connected equipment must be protected locally by a fuse or circuit breaker, whose
G x A x T rating does not exceed 16A. The equipment must be controlled by a switch or switches capable
of interrupting the supply on load; so placed that the switch(es) are in a readily accessible position;
Only the correction factor applicable is placed in the formula. No derating factor is used if the and so placed that the operator of the switch(es) is not placed in danger. The means of switching
cables are in contact on one side only with thermal insulation, since current-carrying capacity may be placed in the appliance. (476-03-04.)
tables are provided for this condition. No further diversity is allowed, since this has already been
taken into account in multiplying l
n
x 0.67. Only 2 pole-and-earth contact plugs with single pole fusing on the live pole are to be used in a
circuit where one pole of the supply is earthed.
Spurs off the Ring
The total number of fused spurs is unlimited, but the following minimum cable sizes shall be used
Such socket outlets shall have a raised socket keys to prevent the insertion of non-fused plugs.
if a fused spur feeds the socket outlets.
(See previous pages.)
2 Lighting circuits
1.5 mm for pvc insulated copper cables.
2
Lampholders which are within 2.5 metres of a fixed bath or shower shall be constructed of, or
1 mm for micc copper conductor cable.
shrouded in, insulating material, and have an insulating shroud. Alternatively, luminaires that are
totally enclosed may be used.
Fused spurs are connected to the ring circuit through a fused connection unit, the fuse of which
601-11
must not exceed 13A, or the rating of the cable taken from the fused spur.
Lighting switches shall be mounted so that they are inaccessible to a person using a fixed bath or
The number of non-fused spurs must not exceed the total number of socket outlets and stationary
shower. The only part of the switch that is allowed to be accessible is the insulating cord of a cord-
equipment connected directly in the ring circuit.
operated switch complying with BS3676, and switches operated by mechanical actuators with
insulating linkages, or insulated switches which form part of a circuit derived from a SELV safety
A non-fused spur can only feed one single or one twin socket outlet, or one permanently
source with a nominal voltage not exceeding 12V r.m.s. a.c. or d.c.
connected item of equipment.
601-08
The supply for a non –fused spur can be taken from the origin of the circuit in the distribuition
The outer contact of Edison screw or single centre bayonet cap type lampholders in TN and TT
board, or from a junction box, or from socket outlet connected directly to the ring circuit, the
systems shall be connected to the neutral conductor.
conductors used being the same size as the ring circuit.
553-03-04
Permanently connected equipment shall be controlled by a switch or switches, separate from the
Ceiling roses shall not be used in circuits exceeding 250V and not have more than one outgoing
equipment, in an accessible position, and protected by a fuse not exceeding 13A, or a circuit
flexible cord, unless designed for multiple pendants.
breaker not exceeding 16A.
553-04-02, 553-04-03
Please Note: All prices shown exclude V.A.T.
380
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