SECTION 607

EARTHING REQUIREMENTS FOR THE INSTALLATION OF EQUIPMENT HAVING HIGH EARTH LEAKAGE CURRENTS

607-01 Scope

607-01-01 The particular requirements of this section shall apply to every installation supplying equipment having a high earth leakage current (usually exceeding 3.5 mA), including information technology equipment to BS EN 60950 and industrial control equipment where values of earth leakage current in normal service permitted by British Standards necessitate special precautions being taken in the installation of the equipment.

607-02 General

607-02-01 Where a low-noise earth is specified for a particular item of equipment, the requirement of Sections 545 and 546 shall apply.

607-02-02 Except as required by Regulation 607-02-06 no special precaution is necessary for equipment complying with BS EN 60950, and having leakage current not exceeding 3.5 mA.

607-02-03 Where more than one item of stationary equipment having an earth leakage current exceeding 3.5 mA in normal service is to be supplied from an installation incorporating a residual current device, it shall be verified that the total leakage current does not exceed 25 % of the nominal tripping current of the residual current device (see also Regulation 531-02-04).
Where compliance with this regulation cannot be otherwise achieved the items of equipment shall be supplied through a double-wound transformer or equivalent device as described in item (vi) of Regulation 607-02-07.

607-02-04 An item of stationary equipment having an earth leakage current exceeding 3.5 mA but not exceeding 10 mA in normal service shall either be permanently connected to the fixed wiring of the installation without the use of a plug and socket-outlet or shall be connected by means of a plug and socket-outlet complying with BS EN 60309-2.

607-02-05 An item of stationary equipment having an earth leakage current exceeding 10 mA in normal service shall preferably be permanently connected to the fixed wiring of the installation. The permanent connection to the fixed wiring may be by means of a flexible cable. Alternatively one of the following precautions shall be taken:
(i) The equipment may be connected by means of a plug and socket-outlet complying with BS EN 60309-2 provided that the protective conductor of the associated flexible cable is supplemented by a separate contact and a second protective conductor having a cross-sectional area not less than 4 mm 2 or the flexible cable complies with Regulation 607-02-07(iii) with the second protective conductor connected via a separate contact within the plug.
(ii) A monitoring system to BS 4444 may be installed which, in the event of a discontinuity in the protective conductor, automatically disconnects the supply in accordance with Regulation 413-02-01.

607-02-06 For a final circuit supplying a number of socket-outlets in a location intended to accommodate several items of equipment, where it is known or is reasonably to be expected that the total earth leakage current in normal service will exceed 10 mA, the circuit shall be provided with a high integrity protective connection complying with one or more of the arrangements described in items (i) to (vi) of Regulation 607-02-07. Alternatively a ring circuit may be used to supply a number of single socket-outlets. There shall be no spur from the ring and the supply ends of the protective conductor ring shall be separately connected at the distribution board. The minimum size of the
protective earth conductor ring shall be 1.5 mm.

607-02-07 The fixed wiring of every final circuit intended to supply an item of stationary equipment having an earth leakage current exceeding 10 mA in normal service shall be provided with a high integrity protective connection complying with one or more of the arrangements described in items (i) to (vi) below:
(i) A single protective conductor with a cross-sectional area of not less than 10 mm
(ii) Separate duplicated protective conductors, having independent connections complying with Regulation 526-01, each having a cross-sectional area not less than 4 mm
(iii) Duplicate protective conductors incorporated in a multicore cable together with the live conductors of the circuit, provided that the total cross-sectional area of all the conductors of the cable is not less than 10 mm 2. One of the protective conductors may be formed by a metallic armour, sheath or braid incorporated in the construction of the cable and complying with Regulation 543-02-05
(iv) Duplicate protective conductors formed by metal conduit, trunking or ducting complying with Regulation 543-02-04, and by a conductor having a cross-sectional area not less than 2.5 mm 2 installed in the same enclosure and connected in parallel with it
(v) An earth monitoring device which, in the event of a discontinuity in the protective conductor, automatically disconnects the supply of the equipment in accordance with Regulations 413-02-01 to 413-02-26
(vi) Connection of the equipment to the supply by means of a double-wound transformer or other unit in which the input and output circuits are electrically separated, the circuit protective conductor is 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 shall comply with one of the arrangements described in items (i) to (iv) above.
Except where Regulation 607-02-05 applies each protective conductor mentioned in items (i) to (iv) above shall comply with the requirements of Regulation 607-02-06.