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

(b) In conduit, duct, ducting or trunking systems, if common boxes,
switchplates or blocks are used for mounting controls or outlets for
Category 1 and Category 2 circuits, rigid partition screens or barriers
should be provided between the cables and connections of the two
categories of circuits.
(3) Category 3 and Category 1 & 2 circuits (with enclosures)
(a) Segregation between Category 3 and Category 1 & 2 circuits (with
enclosures) should be in compliance with one of the permissible
arrangements listed in Table 5(2).
(b) Cables of Category 1 circuits are not allowed to be drawn into the
same conduit, duct or ducting as cables of Category 3 circuits.
(c) Cores of Category 1 and Category 3 circuits are not allowed to be
contained in a common multicore cable, flexible cable or flexible cord.
(4) Category 1, 2 and 3 circuits without enclosure or underground
For cables of Category 1, 2 and 3 circuits that are installed without
enclosure or underground, the following requirements should be
observed:
(a) A minimum horizontal and vertical separation distance of 50 mm
should be provided between Category 1, 2 and 3 circuits.
(b) For cables laid underground or in trench, if the separation distance
of 50 mm cannot be achieved, a separation distance of not less than
25 mm is acceptable provided slabs of concrete are inserted
between Category 1, 2 and 3 circuits. The slabs should be of such
width and length that at every point, the shortest path between the
circuits round the concrete should exceed 75 mm.
(c) At point(s) of crossing for surface wiring of Category 1, 2 and 3
circuits, a bridge of durable insulating material at least 6 mm thick
should be used for separation of circuits. The bridge should overlap
the cables of those circuits by at least 25 mm on either side of the
point of crossing.
5C Segregation of Category 4 Circuits and Circuits of Other
Categories
(a) Cables of Category 4 circuits are not allowed to be drawn into the
same conduit, duct, ducting or trunking as cables of other circuit
categories.
(b) Cores of Category 4 circuits and cores of other circuit categories are
not allowed to be contained in a common multicore cable, flexible
cable or flexible cord.
(c) For cables of Category 4 that are installed underground or without
any enclosure, the following points should be observed:
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