Section
5 Supply and distribution
5.1 Systems of supply and distribution
5.1.1 The
following systems of generation and distribution are acceptable, other
than for tankers intended for the carriage in bulk of oil, liquefied
gases and other hazardous liquids having a flash point not exceeding
60°C (closed-cup test):
-
d.c., two-wire,
-
a.c., single-phase,
two-wire;
-
a.c., three-phase;
-
three-wire;
-
four-wire
with neutral solidly earthed but without hull return.
5.1.2 For
tankers intended for the carriage in bulk of oil, liquefied gases
and other hazardous liquids having a flash point not exceeding 60°C
(closed-cup test) only the following systems of generation and distribution
are acceptable:
-
d.c., two-wire,
insulated;
-
a.c., single-phase,
two-wire, insulated;
-
a.c., three-phase,
three-wire, insulated;
-
earthed systems,
a.c. or d.c., limited to areas outside any hazardous space or zone,
and arranged so that no current arising from an earth-fault in any
part of the system could pass through a hazardous space or zone;
-
earthed systems,
complying with Pt 6, Ch 2, 5.1 Systems of supply and distribution 5.1.1 and Pt 6, Ch 2, 5.5 Earthed distribution systems 5.5.7, provided the Government of
the Flag State permits such an arrangement in accordance with the 'Equivalents' provisions of SOLAS Chapter I - General provisions,
Regulation 5, see
Ch 1, 1.4 Equivalents of
the Rules for Ships for Liquid Chemicals and/or the the Rules for
Ships for Liquefied Gases, as appropriate, see also
Pt 6, Ch 2, 14.1 General 14.1.2.
Earthed intrinsically safe circuits are permitted to pass into
and through hazardous spaces and zones.
5.1.3 System
voltages for both alternating current and direct current in general
are not to exceed:
- 35000 V for power distribution;
- 15 000 V for generation and propulsion;
- 500 V for cooking and heating equipment permanently connected
to fixed wiring;
- 250 V for lighting, heaters in cabins and public rooms, and other
applications not mentioned above.
Voltages above these will be the subject of special consideration.
5.1.4 The
arrangement of the main system of supply is to be such that a fire
or other casualty in any space containing the main source of electrical
power, associated converting equipment, if any, the main switchboard
and the main lighting switchboard will not render inoperable any emergency
service, other than those located within the space where the fire
or casualty has occurred.
5.1.5 The
main switchboard is to be so placed relative to the main source of
power that, as far as is practicable, the integrity of the main system
of supply will be affected only by a fire or other casualty in one
space.
5.1.6 The
arrangement of the emergency system of supply is to be such that a
fire or other casualty in spaces containing the emergency source of
electrical power, associated converting equipment, if any, the emergency
switchboard and the emergency lighting switchboard, will not cause
loss of services required to maintain the propulsion and safety of
the ship.
5.1.7 Distribution
systems required in an emergency are to be so arranged that a fire
in any one main fire zone, as defined by SOLAS 1974 as amended Regulation 3 - Definitions, will not interfere
with the emergency distribution in any other such zone.
5.2 Essential services
5.2.1 Essential
services that are required by Pt 5 Main and Auxiliary Machinery to
be duplicated are to be served by individual circuits, separated in
their switchboard or section board and throughout their length as
widely as is practicable without the use of common feeders, protective
devices, control circuits or controlgear assemblies, so that any single
fault will not cause the loss of both services.
5.2.2 Where Pt 6, Ch 2, 5.2 Essential services 5.2.1 is applicable the main busbars
of the switchboard, or section boards, are to be capable of being
split, by a multipole linked circuit breaker, disconnector or switch-disconnector,
into at least two independent sections, each supplied by at least
one generator, either directly or through a converter. The essential
services are to be equally divided, as far as is practicable, between
the independent sections.
5.2.3 Where Pt 6, Ch 2, 5.2 Essential services 5.2.2 is applicable provision is
to be made to transfer to a temporary circuit those essential services
which are not required to be, and have not been, duplicated in the
event of loss of their normal section of switchboard or section-board.
5.3 Isolation and switching
5.3.2 Isolation
and switching is to be by means of a circuit-breaker or switch arranged
to open and close simultaneously all insulated poles. Where a switch
is used as the means of isolation and switching, it is to be capable
of:
-
switching off
the circuit on load;
-
withstanding,
without damage, the overcurrents which may arise during overloads
and short-circuit.
In addition, these requirements do not preclude the provision
of single pole control switches in final sub-circuits, for example
light switches. For circuit-breakers, see
Pt 6, Ch 2, 6.5 Circuit-breakers and Pt 6, Ch 2, 7.3 Circuit-breakers.
5.3.3 Provision
is to be made, in accordance with one of the following, to prevent
any circuit being inadvertently energised:
-
the circuit-breaker
or switch can be withdrawn, or locked in the open position;
-
the operating
handle of the circuit-breaker or switch can be removed;
-
the circuit fuses,
where fitted, can be readily removed and retained by authorised personnel.
5.3.4 Where
arrangements are in place for automatic changeover between two or
more supplies of electrical power in the event of failure of one supply,
the arrangements are to be such that a fault in one feeder does not
result in the loss of all supplies to the automatic changeover switch.
5.3.6 The
switching device required by Pt 6, Ch 2, 5.3 Isolation and switching 5.3.5 is
to be situated within or adjacent to the section board, distribution
board or item of equipment. Where necessary, interlocking arrangements
are to be provided to prevent circuits being inadvertently energised.
5.3.7 A notice
is to be fixed to any section board, distribution board or item of
equipment to which Pt 6, Ch 2, 5.3 Isolation and switching 5.3.5 applies
warning personnel before gaining access to live parts of the need
to open the appropriate circuit-breakers or switches, unless an interlocking
arrangement is provided so that all circuits concerned are isolated
before access is gained.
5.3.9 Where
high voltage equipment is contained in a room or protected area which
also forms its enclosure, the access door(s) of the space is to be
so interlocked that it cannot be opened until:
- the high voltage supply(ies) to the equipment is switched off;
- the equipment and its cable(s) are earthed down to dissipate
stored energy sufficient to ensure personnel safety.
5.3.11 High voltage switchgear and controlgear assemblies that use liquids or gasses other than
ambient air as an insulating medium are to be installed in spaces that are adequately
protected according to the following requirements:
- The space is to be provided with ventilation to ensure that gasses cannot accumulate
unnoticed.
- Leakages of liquid are to be properly collected and contained.
- An alarm is to be initiated at a manned control station to indicate when the
insulating medium has reduced to an abnormally low level. Interlocks are to be
provided to ensure that the switchgear or controlgear cannot be closed when this
alarm is active. The interlocks are to ensure that services essential for the
propulsion and safety of the ship are not disconnected in the event of this alarm
being activated.
5.4 Insulated distribution systems
5.4.1 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 engine control room, or equivalent attended position,
in the event of an abnormally low level of insulation resistance, see
also
Pt 6, Ch 1, 4.2 Alarm system for machinery.
5.4.2 Where
any insulated lower voltage system is supplied through transformers
from a high voltage system, adequate precautions are to be taken to
prevent the low voltage system being charged by capacitive leakage
from the high voltage system.
5.4.4 Where
filters are fitted, for example to reduce EMC susceptibility, these
are not to cause distribution systems to be unintentionally connected
to earth.
5.5 Earthed distribution systems
5.5.1 No fuse,
non-linked switch or non-linked circuit-breaker is to be inserted
in an earthed conductor. Any switch or circuit-breaker fitted is to
operate simultaneously in the earthed conductor and the insulated
conductors. These requirements do not preclude the provision (for
test purposes) of an isolating link to be used only when the other
conductors are isolated.
5.5.2 For
high voltage systems, where the earthed neutral system of generation
and primary distribution is used, earthing is to be through an impedance
in order to limit the total earth fault current to a magnitude which
does not exceed that of the three phase short-circuit current for
which the generators are designed.
5.5.3 Generator
neutrals may be connected in common, provided that the third harmonic
content of the voltage waveform of each generator does not exceed
five per cent.
5.5.4 Where
a switchboard is split into sections operated independently or where
there are separate switchboards, neutral earthing is to be provided
for each section or for each switchboard. Means are to be provided
to ensure that the earth connection is not removed when generators
are isolated.
5.5.5 A means
of isolation is to be fitted in the earthing connection of each generator
so that generators can be completely isolated for maintenance.
5.5.6 All
earthing impedances are to be connected to the hull. The connections
to the hull are to be so arranged that any circulating currents in
the earth connections do not interfere with radio, radar, communication
and control equipment circuits.
5.6 Diversity factor
5.6.1 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.
5.6.2 A diversity
factor may be applied to the calculation for size of cable and rating
of switchgear and fusegear, taking into account the duty cycle of
the connected loads and the frequency and duration of any motor starting
loads.
5.6.3 For
winches and crane motors the diversity factor is to be calculated
and submitted when required.
5.7 Lighting circuits
5.7.1 Lighting
circuits are to be supplied by final sub-circuits separate from those
for heating and power. This does not preclude the supply from a lighting
circuit supplying a single fixed appliance, such as a cabin fan, a
dry shaver, a wardrobe or anti-condensation heater, taking a maximum
current of 2 A.
5.7.2 Lighting
for the following spaces is to be supplied from at least two final
sub-circuits in such a way that failure of one of the circuits does
not leave the space in darkness. One of these circuits may be an emergency
circuit provided it is normally energised.
- Spaces that are required to be lit for the safe working of the
ship, such as control stations, normal working spaces, etc.
- Spaces where there may be a hazard due to movement of crew, passengers
and/or equipment, such as in corridors, working passage ways, stairways
leading to boat decks, public rooms, etc.
- Spaces where there may be a hazard due to moving machinery and
hot parts, such as in machinery spaces, workshops, large galleys,
laundries, etc.
5.7.3 Lighting
for enclosed hazardous spaces is to be supplied from at least two
final sub-circuits to permit light from one circuit to be retained
while maintenance is carried out on the other. One of these circuits
may be an emergency circuit, provided it is normally energised in
which case the arrangements are to comply with Pt 6, Ch 2, 3 Emergency source of electrical power.
5.7.5 Lighting
of unattended spaces, such as cargo spaces, is to be controlled by
multipole linked switches situated outside such spaces. Provision
is to be made for the complete isolation of these circuits, and locking
the means of control in the off position.
5.7.6 Where
lighting circuits in the cargo pump-rooms of tankers are also used
for emergency lighting, and have been interlocked with the ventilation,
the interlocking arrangements are:
- not to cause the lighting to go out following a failure of the
ventilation system; and
- not to prevent operation of the emergency lighting following the
loss of the main source of electrical power.
5.8 Motor circuits
5.9 Motor control
5.9.1 Every
electric motor is to be provided with efficient means for 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, 5.9 Motor control 5.9.2.
5.9.2 Means
to prevent undesired restarting after a stoppage due to low volts
or complete loss of volts are to be provided. This does not apply
to motors where a dangerous condition might result from the failure
to restart automatically, e.g. steering gear motor.
5.9.3 Means
for automatic disconnection of the supply in the event of excess current
due to mechanical overloading of the motor are to be provided, see
also
Pt 6, Ch 2, 6.11 Motor circuits.
5.9.4 Motor
controlgear is to be suitable for the starting current and for the
full load rated current of the motor.
5.10 Harmonic distortion measurement
5.10.1 The requirements of Pt 6, Ch 2, 5.10 Harmonic distortion measurement
apply to electrical distribution systems that include harmonic filters. This
requirement applies both to high voltage and low voltage busbars. See also
Pt 6, Ch 2, 6.13 Harmonic filters. Harmonic filters
associated with frequency drives for individual applications (i.e. pump motors) are
excluded from the following requirements.
5.10.2 Means are to be provided to continuously monitor the levels of harmonic distortion
experienced on the main busbars and to operate an alarm in the engine control room,
or equivalent attended position, in the event that the harmonic distortion exceeds
the acceptable limits, see also
Pt 6, Ch 1, 4.2 Alarm system for machinery.
5.10.3 Where the engine room is provided with automation systems to continuously monitor the
levels of harmonic distortion experienced on the main busbars, this reading is to be
logged electronically; otherwise it is to be measured annually and after any
modification to the craft electrical distribution system or associated consumers and
recorded in the engine log book for future inspection by the Surveyor.
5.11 Harmonic filtering
5.11.1 The requirements in this Section apply to systems provided with harmonic
filters. They apply in particular to, but are not limited to, electrical propulsion
systems and are in addition to the requirements for harmonic filters in Pt 6, Ch 2, 6.13 Harmonic filters.
5.11.3 The service life of the harmonic filter is to be declared, and details are to be
included in the harmonic calculation report.
5.11.4 The temperature rating of the harmonic filter is to allow for the increased heating
effect of the harmonic distortion.
5.11.6 The modes of operation of the electrical distribution system for which harmonic
distortion levels at the main switchboard busbars are maintained within the
acceptable limits during normal operation are to be defined by the system
integrator.
5.11.7 Harmonic distortion calculations are to include levels of harmonic distortion
expected in normal operation and in the event of a failure of a harmonic filter or
the failure of any combination of harmonic filters. See also
Pt 6, Ch 2, 21.2 Trials.
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