4. Grounding of Non-Current-Carrying Parts

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4.1 All accessible metal parts of an electrical installation, other than current-carrying parts, shall be grounded.

4.2 Subsection (1) does not apply to:

1. lamp bases;
2. shades, reflectors or guards supported on lamp holders or lighting fittings constructed of or shrouded in non-conducting material,
3. portable appliances having double or reinforced insulation;
4. portable appliances that are protected by isolating transformers;
5. bearing housings that are insulated in order to prevent the circulation of current in the bearings,
6. apparatus supplied at not more than 55 volts; and
7. cable clips;
8. the metal core of the isolating transformer in accordance with Section 11.39 (e) (i) and Figure 11-1.

4.3 The grounding of non-current-carrying parts of electrical equipment shall be effected by the following methods:

1. metal frames or enclosures of apparatus shall be fixed to, and be in metallic contact with the ship's structure, provided that the surfaces in contact are clean and free from rust, scale or paint when installed and are firmly bolted together; alternatively, they shall be connected to the hull, either direct or via the grounding terminal of a receptacle outlet; metallic cable sheath shall not be solely relied upon for this purpose;
2. the metal sheaths and armour of cables shall be grounded by means of glands or connectors intended for the purpose and so designed as to ensure an effective ground connection; the gland shall be firmly attached to, and be effective electrical contact with a metal structure grounded in accordance with these Standards;
3. conduits shall be grounded by being screwed into a metal enclosure, or by nuts on both sides of the wall of a metal enclosure provided the surfaces in contact are clean and free from rust, scale or paint and that the enclosure is grounded in accordance with these Standards;
4. as an alternative to the methods described in paragraphs (b) and (c), cable sheaths, armours and conduit shall be grounded by means of clamps or clips of corrosion-resistant metal, making effective contact with the sheath or armour and grounded metal; and
5. all joints in metal conduits and ducts and in metal sheaths of cables, which are used for ground continuity, shall be soundly made and protected where necessary against corrosion.

4.4 Every grounding conductor shall:

1. be of copper or other corrosion-resistant material,
2. be securely installed and protected where necessary against mechanical damage,
3. where necessary protected against electrolytic corrosion: and,
4. be at least as large as the supply cable to the equipment for cables up to 16 mm² (6 awg ), above 16 mm² (6 awg ) at least one half the size of the supply cable but not less than 16 mm² (6 awg );
5. the conductor shall be a bare copper conductor or if coloured shall be in accordance with Section 12.13.

4.5 On wood and composite ships, a continuous ground conductor shall be installed to facilitate the grounding of non-conducting exposed metal parts; the ground conductor shall terminate at a copper plate area not less than 0.2 m² fixed to the keel below the light waterline so as to be fully immersed under all conditions of heel; the minimum size of the ground conductor shall be not less than 16 mm² (#6 AWG ).

4.6 Every ground connection to the ship's structure or on wood and composite ships to the continuous ground conductor, shall be made in an accessible position and shall be secured by a screw or connector of brass or other corrosion-resistant material used solely for that purpose.

4.7 Metal frames of all portable electric lamps, tools and similar apparatus rated in excess of 50 volts shall be grounded through a suitable conductor unless equivalent safety provisions are made such as by double insulation or by an isolating transformer.

5. Application of Demand Loads

5.1 Generator, bus tie and feeder cables shall be selected on the basis of:

1. a computed load of not less than the demand load specified in Table 5-1; and
2. the drop in voltage from the switchboard busbars to every point on the installation when the conductors are carrying the maximum service, not exceeding:
   1. for lighting circuits, 6% of the nominal voltage; and
   2. for heating and power circuits, 7% of the nominal voltage.

5.2 In the assessment of demand loads for motive-power circuits, the normal full load shall be based on the nameplate rating of motors, and for ac circuits, account shall be taken of the relatively small decrease in current consumption of partially loaded motors.

Table 5-1

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