Section 2 System design - General

2.1.1 The following systems of distribution may be used:

1. Parallel systems with constant voltage

   1. d.c., two-wire

   2. a.c., single-phase, two-wire

   3. a.c., three-phase,

      three-wire

      four-wire with neutral earthed

   Systems employing hull return will be accepted except for final sub-circuits which are to be 2-pole insulated.

2. Series systems with constant current (direct current only).

2.1.2 For parallel systems with constant voltage, system voltages for both alternating current and direct current shall not exceed:

2.1.3 Generation and distribution at higher voltages may be submitted for special consideration.

2.2.1 Every insulated distribution system is to be provided with lamps or other means to indicate the state of insulation to earth.

2.2.2 A device(s) is to be installed for every insulated distribution system, whether primary or secondary, for power, heating and lighting circuits, to continuously monitor the insulation level to earth and to operate an alarm in the event of an abnormally low level of insulation resistance.

2.3.1 The number and rating of the ship’s service generating sets and converting sets are to be sufficient to ensure the operation of services essential for the propulsion and safety of the ship.

2.3.2 On oil tankers, oil and chemical tankers, chemical tankers, cargo and passenger ships where electrical power is required for essential equipment, the generating plant and converting plant is to be of such capacity that this essential equipment can be operated satisfactorily even with one generating set or converting set out of action.

2.3.3 In alternating current systems requiring standby equipment, see Pt 6, Ch 2, 2.3 Number and rating of generating sets 2.3.1, with one generating set out of action, the remaining set(s) are to have sufficient reserve capacity to permit the starting of the largest motor in the ship without causing any motor to stall or any other device to fail due to excessive voltage drop on the system.

2.4.1 All passenger ships are to be provided with an emergency source of electrical power. Location is to be aft of collision bulkhead and A60 separated from main generators and in a watertight separated compartment when available.

2.4.2 Where emergency generating sets are fitted, they are to be capable of being started readily when cold.

2.4.3 If hand starting is demonstrated to be practicable, alternative means of starting are not required. Where hand starting is not practicable, other means are to be provided and, in general, should provide for not less than 12 starts in a period of 30 minutes without recourse to sources within the machinery space.

2.4.4 The power available is to be sufficient to supply all services necessary for the safety of passengers and crew in an emergency, due regard being paid to such services as may have to be operated simultaneously. Special consideration is to be given to emergency lighting in all alleyways, stairways and exits, in the machinery spaces and in the control stations (i.e. spaces in which radio, main navigating or central fire recording equipment or the emergency generator is located), to fire detection and alarm systems, to the emergency fire pump if electrically driven, automatic sprinkler systems, if fitted, and to navigation lights. The power is to be adequate for a period of three hours.

2.4.5 The emergency source of power is to be either:

1. A generator driven by a suitable prime mover with an independent fuel supply and with satisfactory starting arrangements; the fuel used is to have a flash point of not less than 43°C; or

2. An accumulator (storage) battery capable of carrying the emergency load without recharging or excessive voltage drop.

2.4.6 Where the emergency source of power is an accumulator battery, arrangements are to be such that emergency lighting will automatically come into operation on failure of the main lighting supply.

2.4.7 An indicator is to be mounted in the machinery space, or in the wheelhouse, to indicate when any accumulator battery fitted in accordance with Pt 6, Ch 2, 2.4 Emergency source of power in passenger ships 2.4.5 is being discharged.

2.4.8 The emergency switchboard is to be installed as near as is practicable to the emergency source of power.

2.4.9 The emergency switchboard may be supplied from the main switchboard during normal operation.

2.4.10 Emergency source/distribution is to be independent from main source/distribution and main source/distribution is to be independent of emergency source/distribution.

2.5.1 Circuits supplying two or more final sub-circuits are to be rated in accordance with the total connected load subject, where justified, to the application of a diversity factor. Where spare ways are provided on a section or distribution board, an allowance for future increase of load is to be added to the total connected load before application of any diversity factor.

2.5.2 The diversity factor may be applied to the calculation for size of cable and rating of switchgear and fusegear.

2.6.1 A separate final sub-circuit is to be provided for every motor required for essential services.

2.7.1 Lighting circuits are to be supplied by final sub-circuits separate from those for heating and power. (This does not apply to cabin fans and wardrobe heaters).

2.7.2 A final sub-circuit of rating exceeding 15 A is not to supply more than one point. The number of lighting points supplied by a final sub-circuit of rating 15 A or less is not to exceed:

except that in final sub-circuits for cornice lighting, panel lighting and electric signs where lampholders are closely grouped, the number of points supplied is unrestricted, provided the maximum operating current in the sub-circuit does not exceed 10 A.

2.7.3 Lighting of cargo spaces is to be controlled by multi-pole linked switches situated outside these spaces. Provision is to be made for the complete isolation of these circuits and locking in the off position of the means of control.

2.7.4 Emergency lighting is to be fitted in accordance with Pt 6, Ch 2, 2.4 Emergency source of power in passenger ships 2.4.4.

2.8.1 Where electrical control of the steering system is fitted, an independent alternative control system is to be installed. This may be a duplicate electrical control system or control by other means.

2.8.2 Provision should be made on the bridge to effectively transfer the steering control instantaneously to the alternative means of control.

2.8.3 Indicators for running indication of steering gear motors are to be installed on the bridge.

2.8.4 Audible and visual alarms are to operate at the steering position(s) for the following fault conditions:

1. Failure of steering gear power system(s).

2. Failure of steering gear control system(s).

2.9.1 Where electrically driven emergency fire pumps are installed in accordance with Pt 6, Ch 2, 17.4 Emergency services 17.4.1, the supply to such pumps is not to pass through the main machinery spaces.

2.9.2 Any fire-alarm system is to operate both audible and visual signals at the fire detection control station(s).

2.10.1 Each navigation light is to be controlled and protected in each insulated pole by a switch and fuse or circuit-breaker mounted in the distribution board.

2.10.2 Automatic indication of failure is to be provided unless lights are visible from the bridge.

2.10.3 Any Statutory Requirements of the country of registration are to be complied with and may be accepted as an alternative to the above.

2.11.1 Means are to be provided for stopping ventilating fans serving machinery and cargo spaces. These means are to be capable of being operated from outside such spaces in case of fire.

2.11.2 Machinery driving boiler fans, independently driven pumps delivering oil to main propulsion machinery for bearing lubrication and piston cooling, fuel oil transfer pumps and other similar fuel pumps are to be fitted with remote controls situated outside the space concerned so that they may be stopped in the event of fire arising in the space in which they are located.

2.11.3 In passenger ships, all power ventilation systems, except cargo and machinery space ventilation, which is to be in accordance with Pt 6, Ch 2, 2.11 Remote stops for ventilating fans and pumps 2.11.1, are to be fitted with master controls so that all fans may be stopped from either of two separate positions which are to be situated as far apart as practicable.

2.12.1 Every electric motor is to be provided with efficient means of starting and stopping so placed as to be easily operated by the person controlling the motor. Every motor above 0,5 kW is to be provided with control apparatus as given in Pt 6, Ch 2, 2.12 Motor control 2.12.2 .

2.12.2 Means are to be provided to prevent undesired restarting after a stoppage due to low volts or complete loss of volts. This does not apply to motors, the continuous availability of which is essential to the safety of the ship.

2.12.3 Efficient means of isolation are to be provided so that all voltage may be cut off from the motor and any associated apparatus including any automatic circuit-breaker.

2.12.4 Where the primary means of isolation (that provided at the switchboard, section board or distribution fuse board) is remote from a motor, one of the following is to be provided:

1. An additional means of isolation fitted adjacent to the motor; or

2. provision made for locking the primary means of isolation in the OFF position; or

3. provision made so that the fuses in each line can be readily removed and retained by authorized personnel.

2.12.5 Means are to be provided for automatic disconnection of the supply in the event of excess current due to mechanical overloading of the motor.

2.12.6 Where fuses are used to protect polyphase motor circuits, means are to be provided to protect the motor against unacceptable overload in the case of single phasing.

2.12.7 When motor controlgear is being selected, the maximum current of a motor is to be taken as the full load rated current of the motor.

2.13.1 Where batteries are used for starting main engines, they are to be of adequate capacity to meet the requirements of Pt 5, Ch 2, 9 Starting arrangements, air compressors and batteries.

2.13.2 Adequate charging facilities are to be provided, and where batteries are charged from line voltage, by means of a series resistor, protection against reversal of current is to be provided when the charging voltage is 20 per cent of line voltage or higher.

2.13.3 In direct current systems, means are to be provided to isolate the batteries from the low voltage system when being charged from a higher voltage system.

2.14.1 For the requirements of the provision of a communication system on board passenger ships, see Pt 6, Ch 2, 17.5 Passenger and crew warning system and Pt 6, Ch 2, 17.6 General emergency alarm system.

2.15.1 Each item of heating or cooking equipment is to be controlled as a complete unit by a multi-pole linked switch mounted in the vicinity of the equipment. In the case of cabin heaters a single-pole switch will be acceptable.

2.16.1 Where arrangements are made for the supply of electricity from a source on shore or elsewhere, a suitable connection box is to be installed in a position in the ship suitable for the convenient connection of flexible cables from the external source and containing a circuit-breaker or isolating switch and fuses and terminals of ample size and suitable shape to facilitate a satisfactory connection. Suitable cables, permanently fixed, are to be provided connecting the terminals to a linked switch and/or a circuit-breaker at the main switchboard.

2.16.2 An earth terminal is to be provided for connecting the hull to the shore earth.The shore connection is to be provided with an indicator at the main switchboard in order to show when the cable is energized.

2.16.3 The shore connection is to be provided with an indicator at the main switchboard in order to show when the cable is energized.

2.16.4 Means are to be provided for checking the polarity (for direct current) or the phase sequence (for three – phase alternating current) of the incoming supply in relation to the ship’s system.

2.16.5 At the connection box, a notice is to be provided giving full information on the system of supply and the normal voltage (and frequency, if alternating current) of the ship’s system and the procedure for carrying out the connection.

2.16.6 Alternative arrangements may be submitted for consideration.

2.17.1 Cables are to be in accordance with an acceptable National or International Standard, due regard being given to the ambient conditions stated in Pt 6, Ch 2, 1.5 Ambient temperatures 1.5.1.

2.17.2 The rated voltage of any cable is to be not lower than the nominal voltage of the circuit for which it is used.

2.18.1 The rated operating temperature of the insulating material is to be at least 10°C higher than the maximum ambient temperature liable to be produced in the space where the cable is installed.

2.19.1 Cables fitted in the following locations:

or in any other location where water condensation or harmful vapour (e.g. oil vapour) may be present are to have an impervious sheath. In permanently wet situations, metallic sheaths are to be used for cables with hygroscopic insulation.

2.19.2 All cables are to be of flame-retardant or of fire-resisting type, except that flame-extending cables may be used for final circuits where cables are installed in metallic conduits having an internal diameter not exceeding 25 mm and provided the conduits are mechanically and electrically continuous.

2.20.1 The highest continuous load carried by a cable is not to exceed its current rating. The diversity factor of the individual loads and the duration of the maximum demand may be allowed for in estimating the maximum continuous load and is to be shown on plans submitted for approval.

2.20.2 The voltage drop from the main switchboard busbars to any point in the installation when the cables are carrying maximum current under normal conditions of service, is not to exceed six per cent of the nominal voltage.

2.20.3 In assessing the current rating of lighting circuits, every lampholder is to be assessed at the maximum load likely to be connected to it, with a minimum of 60 W, unless the fitting is so connected as to take only a lamp rated at less than 60 W.

2.20.4 Cables supplying cargo winches, cranes, windlasses and capstans are to be suitably rated for their duty. Unless the duty is such as to require a longer time rating, cables for winch or crane motors may be half hour rated on the basis of the half hour kW rating of the motors. Cables for windlass and capstan motors are to be not less than one hour rated on the basis of the one hour kW rating of the motor. In all cases the rating is to be subject to the voltage drop being within the specified limits.

2.20.5 The current ratings given in Table 2.2.2 General purpose rubber and PVC are based on maximum operating conductor temperatures given in Table 2.2.1 Maximum operating conductor. Alternatively, current rating in accordance with an acceptable National or International Standard may be applied, see Pt 6, Ch 2, 2.17 Choice of cables 2.17.1.

2.21.1  Ambient temperature. When it is known that the ambient temperature is different from that given in Pt 6, Ch 2, 1.5 Ambient temperatures, correction factors shown in Table 2.2.7 Correction factors for ambient are to be applied.

2.21.2  Intermittent service. Where the load is intermittent, the correction factors in Table 2.2.8 Correction factors for intermettent may be applied for half hour and one hour ratings. In no case is a shorter rating than one half hour rating to be used, whatever the degree of intermittency.

2.22.1 Cables having insulating materials with different maximum-rated conductor temperatures are not to be bunched together, or where this is not practicable, the cables are to be so operated that no cable reaches a temperature higher than that permitted for the lowest temperature-rated cable in the group.

2.23.1 Cables are to be suitable for use in the connections between entrained ships, i.e. are to be flexible, robust and of commensurate cross-section area.

2.23.2 The connection is to include provisions for the continuity of out-of-balance or earth-fault current return. The connecting device is to include provisions to ensure that this circuit is closed before, and opened after, the live circuits.

2.23.3 Terminal plugs and sockets, if used, are to be so arranged that any exposed pins cannot be energized, see Pt 6, Ch 2, 10.3 Socket outlets and plugsfor additional requirements.

2.23.4 Where hull-return systems are used, hull polarity is to be compatible.