Part A - General

  12.1.1 Electrical installations ^footnoteshould be such that:

• .1 all electrical auxiliary services necessary for maintaining the craft in normal operation and habitable conditions will be ensured without recourse to the emergency source of electrical power;

• .2 electrical services essential for safety will be ensured under various emergency conditions, and

• .3 the safety of passengers, crew and craft from electrical hazards will be ensured.

The FMEA should include the electrical system, taking into account the effects of electrical failure on the systems being supplied. In cases where faults can occur without being detected during routine checks on the installations, the analysis should take into account the possibility of faults occurring simultaneously or consecutively.

  12.1.2 The electrical system should be designed and installed so that the probability of the craft being at risk of failure of a service is extremely remote.

  12.1.3 Where loss of particular essential service would cause serious risk to the craft, the service should be fed by at least two independent circuits fed in such a way that no single failure in the electrical supply or distribution systems would effect both supplies.

  12.1.4 The securing arrangements for heavy items, i.e. accumulator batteries, should, as far as practicable, prevent excessive movement during the accelerations due to grounding or collision.

  12.1.5 Precautions should be taken to minimize risk of supplies to essential and emergency services being interrupted by the inadvertent or accidental opening of switches or circuit breakers.

  12.2.1 A main source of electrical power of sufficient capacity to supply all those services mentioned in 12.1.1 should be provided. The main source of electrical power should consist of at least two generating sets.

  12.2.2 The capacity of these generating sets should be such that in the event of any one generating set being stopped or failing it will still be possible to supply those services necessary to provide the normal operational conditions of propulsion and safety. Minimum comfortable conditions of habitability should also be ensured which include at least adequate services for cooking, heating, domestic refrigeration, mechanical ventilation, sanitary and fresh water.

  12.2.3 The arrangements of the craft's main source of electrical power should be such that the services referred to in 12.1.1.1 can be maintained regardless of the speed and direction of the propulsion machinery or shafting.

  12.2.4 In addition, the generating sets should be such as to ensure that with any one generator or its primary source of power out of operation, the remaining generating set should be capable of providing the electrical services necessary to start the main propulsion plant from dead craft condition. The emergency source of electrical power may be used for the purpose of starting from a dead craft condition if its capability either alone or combined with that of any other source of electrical power is sufficient to provide at the same time those services required to be provided by 12.7.3.1 to 12.7.3.3 or 12.7.4.1 to 12.7.4.4 or 12.8.2.1 to 12.8.2.4.1, as appropriate.

  12.2.5 Where transformers constitute an essential part of the electrical supply system required by this section, the system should be so arranged as to ensure the same continuity of supply as is stated in 12.2.

  12.2.6 A main electric lighting system which should provide illumination throughout those parts of the craft normally accessible to and used by passengers and crew should be supplied from the main source of electrical power.

  12.2.7 The arrangement of the main electric lighting system should be such that a fire or other casualty in spaces containing the emergency source of electrical power, associated transforming equipment, if any, the emergency switchboard and the emergency lighting switchboard will not render inoperative the main electric lighting system required by 12.2.6.

  12.2.8 The main switchboard should be so placed relative to one main generating station that, as far as practicable, the integrity of the normal electrical supply may be affected only by a fire or other casualty in one space. An environmental enclosure for the main switchboard, such as may be provided by a machinery control room situated within the main boundaries of the space, should not be considered as separating the switchboards from the generators.

  12.2.9 The main busbars should normally be subdivided into at least two parts which should be connected by a circuit-breaker or other approved means. So far as is practicable, the connection of generating sets and any other duplicated equipment should be equally divided between the parts. Equivalent arrangements may be permitted to the satisfaction of the Administration.

  12.3.1 A self-contained emergency source of electrical power should be provided.

  12.3.2 The emergency source of electrical power, associated transforming equipment, if any, transitional source of electrical power, emergency switchboard and emergency lighting switchboard should be located above the waterline in the final condition of damage as referred to in chapter 2, operable in that condition and readily accessible.

  12.3.3 The location of the emergency source of electrical power and associated transforming equipment, if any, the transitional source of emergency power, the emergency switchboard and the emergency electrical lighting switchboards in relation to the main source of electrical power, associated transforming equipment, if any, and the main switchboard should be such as to ensure that a fire or other casualty in spaces containing the main source of electrical power, associated transforming equipment, if any, and the main switchboard or in any machinery space will not interfere with the supply, control and distribution of emergency electrical power. As far as practicable, the space containing the emergency source of electrical power, associated transforming equipment, if any, the transitional source of emergency electrical power and the emergency switchboard should not be contiguous to the boundaries of main machinery spaces or those spaces containing the main source of electrical power, associated transforming equipment, if any, or the main switchboard.

  12.3.4 Provided that suitable measures are taken for safeguarding independent emergency operation under all circumstances, the emergency generator, if provided, may be used exceptionally, and for short periods, to supply non-emergency circuits.

  12.3.5 Distribution systems should be so arranged that the feeders from the main and emergency sources are separated both vertically and horizontally as widely as practicable.

  12.3.6 The emergency source of electrical power may be either a generator or an accumulator battery, which should comply with the following:

• .1 Where the emergency source of electrical power is a generator, it should be:

  • .1.1 driven by a suitable prime mover with an independent supply of fuel having a flashpoint which meets the requirements of 7.1.2.2;

  • .1.2 started automatically upon failure of the electrical supply from the main source of electrical power and should be automatically connected to the emergency switchboard. Those services referred to in 12.7.5 or 12.8.3 should then be transferred to the emergency generating set. The automatic starting system and the characteristic of the prime mover should be such as to permit the emergency generator to carry its full rated load as quickly as is safe and practicable, subject to a maximum of 45 s; and

  • .1.3 provided with a transitional source of emergency electrical power according to 12.7.5 or 12.8.3.

• .2 Where the emergency source of electrical power is an accumulator battery, it should be capable of:

  • .2.1 carrying the emergency electrical load without recharging while maintaining the voltage of the battery throughout the discharge period within 12% above or below its nominal voltage;

  • .2.2 automatically connecting to the emergency switchboard in the event of failure of the main source of electrical power; and

  • .2.3 immediately supplying at least those services specified in 12.7.5 or 12.8.3.

  12.3.7 The emergency switchboard should be installed as near as is practicable to the emergency source of electrical power.

  12.3.8 Where the emergency source of electrical power is a generator, the emergency switchboard should be located in the same space unless the operation of the emergency switchboard would thereby be impaired.

  12.3.9 No accumulator battery fitted in accordance with this section should be installed in the same space as the emergency switchboard. An indicator should be mounted in a suitable space at the craft's operating compartment to indicate when the batteries constituting either the emergency source of electrical power or the transitional source of emergency electrical power referred to in 12.3.6.1.3 are being discharged.

  12.3.10 The emergency switchboard should be supplied during normal operation from the main switchboard by an interconnector feeder which should be adequately protected at the main switchboard against overload and short circuit and which should be disconnected automatically at the emergency switchboard upon failure of the main source of electrical power. Where the system is arranged for feedback operation, the interconnector feeder should also be protected at the emergency switchboard at least against short circuit. Failure of the emergency switchboard, when being used in other than an emergency, should not put at risk the operation of the craft.

  12.3.11 In order to ensure ready availability of the emergency source of electrical power, arrangements should be made, where necessary, to disconnect automatically non-emergency circuits from the emergency switchboard to ensure that power should be available to the emergency circuits.

  12.3.12 The emergency generator and its prime mover and any emergency accumulator battery should be so designed and arranged as to ensure that they will function at full rated power when the craft is upright and when the craft has a list or trimming accordance with 9.1.12 including any damage cases considered in chapter 2, or is in any combination of angles within those limits.

  12.3.13 Where accumulator batteries are installed to supply emergency services, provisions should be made to charge them in situ from a reliable on-board supply. Charging facilities should be designed to permit the supply of services, regardless of whether battery is on charge or not. Means should be provided to minimize the risk of overcharging or overheating the batteries. Means for efficient air ventilation should be provided.

  12.4.1 Emergency generating sets should be capable of being readily started in their cold condition at a temperature of 0°C. If this is impracticable, or if lower temperatures are likely to be encountered, provisions should be made for heating arrangements to ensure ready starting of the generating sets.

  12.4.2 Each emergency generating set should be equipped with starting devices with a stored energy capability of at least three consecutive starts. The source of stored energy should be protected to preclude critical depletion by the automatic starting system, unless a second independent means of starting is provided. A second source of energy should be provided for an additional three starts within 30 min, unless manual starting can be demonstrated to be effective.

  12.4.3 The stored energy should be maintained at all times, as follows:

• .1 electrical and hydraulic starting systems should be maintained from the emergency switchboard;

• .2 compressed air starting systems may be maintained by the main or auxiliary compressed air receivers through a suitable nonreturn valve or by an emergency air compressor which, if electrically driven, is supplied from the emergency switchboard:

• .3 all of these starting, charging and energy storing devices should be located in the emergency generator space. These devices should not be used for any purpose other than the operation of the emergency generating set. This does not preclude the supply to the air receiver of the emergency generating set from the main or auxiliary compressed air system through the nonreturn valve fitted in the emergency generator space.

  12.5.1 Where steering and/or stabilization of a craft is essentially dependent on one device as with a single rudder or pylon, which is itself dependent on the continuous availability of electric power, it should be served by at least two independent circuits one of which should be fed either from the emergency source of electric power or from an independent power source located in such a position as to be unaffected by fire or flooding affecting the main source of power. Failure of either supply should not cause any risk to the craft or passengers during switching to the alternative supply and such switching arrangements should meet the requirements in 5.2.5. These circuits should be provided with short circuit protection and an overload alarm.

  12.5.2 Protection against excess current may be provided, in which case it should be for not less than twice the full load current of the motor or circuit so protected, and should be arranged to accept the appropriate starting current with a reasonable margin. Where three-phase supply is used, an alarm should be provided in a readily observed position in the craft's operating compartment that will indicate failure of any one of the phases.

  12.5.3 Where such systems are not essentially dependent on the continuous availability of electric power but at least one alternative system, not dependent on the electric supply is installed, then the electrically powered or controlled system may be fed by a single circuit protected in accordance with 12.5.2.

  12.5.4 The requirements of chapters 5 and 16 for power supply of the directional control system and stabilization system of the craft should be met.

  12.6.1.1 Exposed metal parts of electrical machines or equipment which are not intended to be live but which are liable under fault conditions to become live should be earthed unless the machines or equipment are:

• .1 supplied at a voltage not exceeding 55 V direct current or 55 V root mean square between conductors; auto-transformers should not be used for the purpose of achieving this voltage; or

• .2 supplied at a voltage not exceeding 250 V by safety isolating transformers supplying only one consuming device; or

• .3 constructed in accordance with the principle of double insulation.

  12.6.1.2 The Administration may require additional precautions for portable electrical equipment for use in confined or exceptionally damp spaces where particular risks due to conductivity may exist.

  12.6.1.3 All electrical apparatus should be so constructed and so installed as not to cause injury when handled or touched in the normal manner.

  12.6.2 Main and emergency switchboards should be so arranged as to give easy access, as may be needed, to apparatus and equipment, without danger to personnel. The sides and the rear and, where necessary, the front of switchboards should be suitably guarded. Exposed live parts having voltages to earth exceeding a voltage to be specified by the Administration should not be installed on the front of such switchboards. Where necessary, nonconducting mats or gratings should be provided at the front and rear of the switchboard.

  12.6.3 When a distribution system, whether primary or secondary, for power, heating or lighting, with no connection to earth is used, a device capable of continuously monitoring the insulation level to earth and of giving an audible or visual indication of abnormally low insulation values should be provided. For limited secondary distribution systems the Administration may accept a device for manual checking of the insulation level.

  12.6.5.1 Each separate circuit should be protected against short circuit and against overload, except as permitted in 12.5, or where the Administration may exceptionally otherwise permit.

  12.6.5.2 The rating or appropriate setting of the overload protective device for each-circuit should be permanently indicated at the location of the protective device.

  12.6.5.3 When the protective device is a fuse it should be placed on the load side of the disconnect switch serving the protected circuit.

  12.6.6 Lighting fittings should be so arranged as to prevent temperature rises which could damage the cables and wiring, and to prevent surrounding material from becoming excessively hot.

  12.6.7 All lighting and power circuits terminating in a bunker or cargo space should be provided with a multiple-pole switch outside the space for disconnecting such circuits.

  12.6.8.1 Accumulator batteries should be suitably housed, and compartments used primarily for their accommodation should be properly constructed and efficiently ventilated.

  12.6.8.2 Electrical or other equipment which may constitute a source of ignition of flammable vapours should not be permitted in these compartments except as permitted in 12.6.9.

  12.6.8.3 Accumulator batteries should not be located in crew accommodation.

  12.6.9 No electrical equipment should be installed in any space where flammable mixtures are liable to collect including those in compartments assigned principally to accumulator batteries, in paint lockers, acetylene stores or similar spaces, unless the Administration is satisfied that such equipment is:

• .1 essential for operational purposes;

• .2 of a type which will not ignite the mixture concerned;

• .3 appropriate to the space concerned; and

• .4 appropriately certified for safe usage in the dusts, vapours or gases likely to be encountered.

  12.6.10 The following additional requirements from .1 to .7 should be met, and requirements from .8 to .13 should be met also for non-metallic craft:

• .1 The electrical distribution voltages throughout the craft may be either direct current or alternating current and should not exceed:

  • .1.1 500 V for power, cooking, heating and other permanently connected equipment; and

  • .1.2 250 V for lighting, internal communications and receptacle outlets.

  The Administration may accept higher voltage for propulsion purposes.

• .2 For electrical power distribution, two-wire, three-wire or four-wire insulated systems should be used. Where applicable, the requirements of 7.5.6.4 or 7.5.6.5 should also be met.

• .3 Effective means should be provided so that voltage may be cut off from each and every circuit and sub-circuit and from all apparatus as may be necessary to prevent danger.

• .4 Electrical equipment should be so designed that the possibility of accidentally touching live parts, rotating or moving parts as well as heated surfaces which might cause burns or initiate fire is minimized.

• .5 Electrical equipment should be adequately secured. The probability of fire or dangerous consequences arising from damage to electrical equipment should be reduced to an acceptable minimum.

• .6 The rating or appropriate setting of the overload protective device for each circuit should be permanently indicated at the location of the protection device.

• .7 Where it is impracticable to provide electrical protective devices for certain cables supplied from batteries, e.g. within battery compartments and in engine starting circuits, unprotected cable runs should be kept as short as possible and special precautions should be taken to minimize risk of faults, e.g. use of single core cables with additional sleeve over the insulation of each core, with shrouded terminals.

• .8 In order to minimize the risk of fire, structural damage, electrical shock and radio interference due to lightning strike or electrostatic discharge, all metal parts of the craft should be bonded together, in so far as possible in consideration of galvanic corrosion between dissimilar metals, to form a continuous electrical system, suitable for the earth return of electrical equipment and to connect the craft to the water when water-born. The bonding of isolated components inside the structure is not generally necessary, except in fuel tanks.

• .9 Each pressure refuelling point should be provided with a means of bonding the fuelling equipment to the craft.

• .10 Metallic pipes capable of generating electrostatic discharges, due to the flow of liquids and gases should be bonded so as to be electrically continuous throughout their length and should be adequately earthed.

• .11 Primary conductors provided for lightning discharge currents should have a minimum cross section of 50 mm² in copper or equivalent surge carrying capacity in aluminium.

• .12 Secondary conductors provided for the equalization of static discharges, bonding of equipment, etc., but not for carrying lightning discharges should have a minimum cross section of 5 mm² copper or equivalent surge current carrying capacity in aluminium.

• .13 The electrical resistance between bonded objects and the basic structure should not exceed 0.05 Ohms except where it can be demonstrated that a higher resistance will not cause a hazard. The bonding path should have sufficient cross-sectional area to carry the maximum current likely to be imposed on it without excessive voltage drop.