Hi Think this should help, I do alot of data centers and all 16amp radials are wired in 4mm for this reason.
607-02-04 The wiring of every final circuit and distribution circuit intended to supply one or more items of equipment, such that the total protective conductor current is likely to exceed 10 mA, shall have a high integrity protective connection complying with one or more of the following:
(i) a single protective conductor having a cross-sectional area of not less than 10 mm2. complying with the requirements of Regulations 543-02 and 543-03
(ii) a single copper protective conductor having a cross-sectional area of not less than 4 mm2, complying with the requirements of Regulations 543-02 and 543-03, the protective conductor being enclosed to provide additional protection against mechanical damage. for example, within a flexible conduit
(iii) two individual protective conductors, each complying with the requirements of Section 543. The two protective conductors may be of different types e.g. a metallic conduit together with an additional conductor of a cable enclosed in the same conduit.
Where the two individual protective conductors are both incorporated in a multicore cable, the total cross sectional area of all the conductors including the live conductors shall be not less than 10 mm2. One of the protective conductors may be formed by the metallic sheath, armour or wire braid screen incorporated in the construction of the cable and complying with Regulation 543-02-05.
(iv) an earth monitoring system to BS 4444 may be installed which, in the event of a continuity fault occurring in the protective conductor, automatically disconnects the supply to the equipment
(v) connection of the equipment to the supply by means of a double wound transformer or equivalent unit, such as a motor-alternator set, the protective conductor of the incoming supply being connected to the exposed-conductive-parts of the equipment and to a point of the secondary winding of the transformer or equivalent device. The protective conductor(s) between the equipment and the transformer or equivalent device shall comply with one of the arrangements described in Regulation 607-02-04 (i) to (iv) above.
607-02-05 Where two protective conductors are used in accordance with Regulation 607-02-04 (iii), the ends of the protective conductors shall be terminated independently of each other at all connection points throughout the circuit. e.g. the distribution board, junction boxes and socket-outlets. This requires an accessory to be provided with two separate earth terminals.
607-03 Socket-outlet final circuits
607-03-01 For a final circuit with a number of socket-outlets or connection units intended to supply several items of equipment. where it is known or reasonably to be expected that the total protective conductor current in normal service will exceed 10 mA, the circuit shall be provided with a high integrity protective conductor connection complying with the requirements of Regulations 607-02 and 607-04. The following arrangements of the final circuit are acceptable:
(i) a ring final circuit with a ring protective conductor. Spurs, if provided, require high integrity protective conductor connection complying with the requirements of Regulation 607-02
(ii) a radial final circuit with a single protective conductor:
(a) the protective conductor being connected as a ring; or
(B) a separate protective conductor being provided at the final socket-outlet by connection to the metal conduit or ducting: or
© where two or more similar radial circuits supply socket-outlets in adjacent areas and are fed from the same distribution board, have identical means of short-circuit and overcurrent protection and circuit protective conductors of the same cross-sectional area, then a second protective conductor may be provided at the final socket-outlet on one circuit by connection to the protective conductor of the adjacent circuit.
(iii) other circuits complying with the requirements of Regulation 607-02.
