Ship Electrical Standards (2002) | TP 127

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Transport Canada > Marine Safety Home Page > Transport Publications | Marine Safety > Ships Electrical Standards (2002) | TP 127 | Marine Safety

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9. SWITCHBOARDS OTHER THAN PROPULSION CONTROL PANELS
SECTION 9

9.1 GENERAL: ^

9.1.1 Every ship's service and emergency generator shall be connected to a main or an emergency switchboard.

9.2 INSTALLATION AND LOCATION: ^

9.2.1 An unobstructed passageway not less than 1 metre wide shall be provided in front of the switchboard; in the case of small ships, if this distance is impracticable, the passageway may be reduced to 0.6 metre.

9.2.2 If access is required at the rear of switchboards, the space shall be sufficient to permit maintenance, and be not less than 0.5 metre clear.

9.2.3 Passageways behind main switchboards shall be of ample height and shall, where practicable, be provided at each end with an access door, fitted with an external lock and such access doors shall bear a prominent and permanent indication of the maximum voltage; in the case of metal clad switchboards that are completely enclosed, access doors need not be fitted;

9.2.4 They shall give easy access from the back, unless designed for installation against bulkheads, and front without danger to personnel;

9.2.5 The sides and backs and, where necessary, the fronts shall be suitably guarded;

9.2.6 A non-conducting mat or grating shall be provided as a floor covering at the front and rear, as necessary;

9.2.7 The switchboard shall be installed in a dry location away from sources of steam, water and oil pipes

9.3 CONSTRUCTION: ^

9.3.1 Main and emergency switchboards shall be arranged as follows:

for voltages between poles or to ground of 50 volts and over, switchboards shall be of a dead front or metal enclosed type; and
a separate cubicle is to be provided for each generator with flame retardant partitions between the different generator cubicles and between cubicles for outgoing circuits; flame retardant partitions are also to be provided between generator control cubicles and associated switchgear; switchboards controlling generators with an aggregate capacity less than 100 kW shall have a flame retardant partition between each generator circuit breaker and outgoing distribution circuits.

9.3.2 Every main and emergency switchboard shall be provided with non-conducting handrails fitted on the front of the panel.

9.3.3 A non-conducting guardrail shall be fitted at the rear of the switchboard if maintenance from the rear is required.

9.3.4 In every ship where the total installed electrical power of the main generator is in excess of 3 megawatts, the main bus bars shall be subdivided into at least two parts which shall normally be connected by means of a circuit breaker or similar device arranged so as to readily disconnect the two parts; so far as is practicable, the connection of generators and any other duplicated equipment shall be equally divided between the parts; equivalent alternative arrangements shall be permitted.

9.3.5 Insulating materials used in the construction of switchboards shall be mechanically strong, flame-retardant, moisture-resistant and have anti-tracking surface finish.

9.3.6 Suitable drip shields shall be provided over switchboards where subject to damage by leaks or falling objects.

9.3.7 Panels shall be of substantial construction to prevent vibration and hinged panels and doors of dead front switchboards shall be provided with positioners and stops.

9.3.8 If drawout generator breakers are not fitted, then disconnect links or an isolating switch shall be fitted.

9.3.9 Switchboard instrumentation and control wiring shall be:

of a type suitable for the service intended with respect to voltage, temperature and grouping;
conductors shall not be smaller than # 18 AWG;
for wiring of printed circuit boards and interconnecting wiring between electronic modules and subassemblies, the conductor shall not be smaller than # 24 AWG;
all conductors shall be capable of passing a vertical flame test in accordance with ANSI/UL 83-1979 (31) or CSA C22.2 No. 127 where applicable and shall be either insulated wire types TA, TBS, TEW, SIS, SEW-2 OR SEWF-2;
connections to hinged panels shall be with the extra flexible type and have mechanical protection at the hinges in order to prevent chafing.

9.3.10 All circuit breakers shall indicate the "OPEN" off position or the "ON" closed position and in addition where circuit breakers are operated vertically rather than rotationally or horizontally the "UP" postion of the operator handle shall be the "ON" position; where the switches are operated horizontally thehandles for a single row shall be to the right for the "ON" position or where two rows are required the "ON" position shall be to the center.

9.4 DESIGN: ^

9.4.1 BUS:

9.4.1. Bus size shall be selected on the basis of limiting the bus-bar temperature rise to 50°C at rated current; Table 9-1 shall be used in determining the necessary bus-bar size; buses shall be designed on the basis of generator capacity and feeder loads; for a single generator, the generator bus shall have a capacity equal to the continuous rating of the generator plus any overload rating in excess of 30 minute duration; for more than one generator with all generating capacity feeding through one section of the bus, the capacity of the bus for the first generator shall be the same as for a single-generator installation; for each subsequent generator, the bus capacity shall be increased by 80 percent of the continuous rating of the added generator; the capacity of connection buses for each generator unit shall be equal to the continuous rating of the generator plus any overload rating in excess of 30 minute duration.

9.4.1.2 The buses of feeder switchboards shall have a capacity of not less than 75% of the combined full-load rated current of all loads including 50% of the rated installed or design reserve spare breaker capacity; the capacity of the feeder buses need not be greater than the generator buses which supply them; bus connections to individual feeder circuit breakers shall be designed on the basis of the frame rating of the breakers when the frame rating is 600 A or less; for frame ratings above 600 A, the bus connections shall not be less than the breaker trip rating.

9.4.1.3 Bolts, nuts and pressure maintaining devices used to maintain contact on bus and connection bars shall be of a non-ferrous material or of steel rendered corrosion resistant by zinc electroplating or an equivalent process; connection between bus bars with a width of 76 mm or larger shall be made with a multi-bolt arrangement.

9.4.1.4 The current rating of the equalizer connection and equalizer switches shall be not less than 1/2 the rated full load current of the largest generator.

TABLE 9-1
Ampere rating of Rectangular Bus Bar Placed on Edge
(Based on 50° C Ambient and 50° C rise)

Number of Bus Bars in Parallel	Size of Bars (inches) mm		Ampere Rating of D.C. Copper Bars	Ampere Rating of A.C. Copper Bars
One	3/4 x 1/8 1 x 1/8 1 1/2 x 1/8 1 1/2 x 3/16 2 x 3/16 1 x 1/4 1 1/2 x 1/4 2 x 1/4 3 x 1/4 4 x 1/4 5 x 1/4 6 x 1/4 8 x 1/4	19.1 x 3.2 25.4 x 3.2 38.1 x 3.2 38.1 x 4.8 50.8 x 4.8 25.4 x 6.4 38.1 x 6.4 50.8 x 6.4 76.2 x 6.4 101.6 x 6.4 127.0 x 6.4 152.4 x 6.4 203.2 x 6.4	250 330 500 580 760 490 685 920 1380 1730 2125 2475 3175	250 330 500 570 745 480 675 900 1280 1650 2000 2300 2875
Two (¼ in. apart 6,4mm)	2 x 1/4 3 x 1/4 4 x 1/4 5 x 1/4 6 x 1/4 8 x 1/4	50.8 x 6.4 76.2 x 6.4 101.6 x 6.4 127.0 x 6.4 152.4 x 6.4 203.2 x 6.4	1525 2225 2800 3100 4000 5100	1450 2050 2550 2975 3450 4250
Three (¼ in. apart 6,4mm )	3 x 1/4 4 x 1/4 5 x 1/4 6 x 1/4 8 x 1/4	76.2 x 6.4 101.6 x 6.4 127.0 x 6.4 152.4 x 6.4 203.2 x 6.4	3035 3875 4700 5500 6875	2550 3225 3880 4400 5300
Four ( ¼,2½,¼ apart) 6.4mm, 63.5, 6.4	3 x 1/4 4 x 1/4 5 x 1/4 6 x 1/4 8 x 1/4	76.2 x 6.4 101.6 x 6.4 127.0 x 6.4 152.4 x 6.4 203.2 x 6.4	3300 4500 5425 6300 7200	3050 4250 5000 6000 7100

9.4.1.5 Switchboard bus-bars and supports shall be of substantial and durable construction and shall be capable of withstanding electromechanical stresses which may arise from short-circuit faults.

9.4.1.6 Bus-bars and their connections shall be of copper, all connections being tinned or silver surfaced so as to inhibit corrosion and reduce contact resistance.

9.4.1.7 Bus-bars, connection bars and wiring on the switchboard shall be arranged so that maximum accessibility is provided for cable connections.

9.4.1.8 Bare main bus-bars in main and emergency switchboards shall have minimum clearances and creepage distances in accordance with the Table 9-2:

TABLE 9-2

Maximum Rated Voltage Between Phases and Poles	Minimum Air Clearance to Ground	Minimum Air Clearance Between Phases and Poles
125	12.5 mm	12.5 mm
250	12.5 mm	19.0 mm
500	22.0 mm	22.0 mm
600	22.0 mm	25.5 mm

9.4.2 INSTRUMENTS, INDICATION and PROTECTIVE DEVICES

9.4.2.1 All switchboard instruments, control circuit fuses, and all apparatus controlling circuits shall be provided with nameplates of durable flame-retardant material bearing clear and indelible indication, including fuse rating.

9.4.2.2 All electrical indicating instruments other than synchroscopes shall preferably be of the 250° nominal scale type.

9.4.2.3 The upper limit of the scale of every ammeter and wattmeter shall be not less than 130% of the normal rating of the circuit in which it is installed and the scale shall be provided with a red line indicating the normal full-load value.

9.4.2.4 The upper limit of every voltmeter shall be not less than 120% of the normal voltage of the circuit and the scale shall be provided with a red line to indicate normal voltage; examples of common system voltages and their corresponding voltmeter scales are given in the Table 9-3

TABLE 9-3

Range of System Voltage	Voltmeter Scale
115 - 220	0 - 150
220 - 240	0 - 300
440 - 480	0 - 600
550 - 600	0 - 750
2400	0 - 3000
4160	0 - 5250

9.4.2.5 Wattmeters for use with generators which may operate in parallel shall be capable of indicating reverse power up to 15% of the rated full-load of the generator.

9.4.2.6 Means to continuously indicate the state of the insulation to ground shall be provided for primary and secondary distribution systems; on an insulated system ground indicating lights may be used; one light to be fitted in each phase or pole; on systems with a grounded neutral an ammeter and ammeter switch shall be provided which will indicate current in the 0 to 10 ampere range; the ammeter switch shall be of the type that has a spring return to "ON" position; the ammeter and current transformer shall be of a design that they are not damaged by fault currents; where the ammeter is located in a remote enclosure from the current transformer, a suitable protective device shall be provided to prevent high voltage in the event of an open circuit; a short circuiting switch shall be connected in parallel with the protective device for manually short circuiting the remote part of the current transformer.

9.4.2.7 Where a ground indicating system using either two or three lamps is adopted, the lamps shall be of the metal filament type each not exceeding 30 watts; systems employing a single lamp shall not be used.

9.4.2.8 Secondary windings of all instrument and control transformers shall be effectively grounded.

9.4.2.9 Fuses of ratings exceeding 320 amperes shall not be used, other than for short-circuit protection.

9.4.2.10 Subject to subsection (4.2.11), over-current protection, independent of that provided for other circuits, shall be provided for circuits containing voltmeters, voltage coils of instruments, primary circuits of voltage transformers, ground indicating lights and pilot lamps and the fuses used for this purpose shall be of adequate breaking capacity and shall be placed as near as practicable to the tapping of the supply.

9.4.2.11 Over-current protection for circuits containing ground indicating lights and pilot lamps shall not also be used for circuits containing voltmeters or voltage coils of instruments and protective devices except when the lamp is an integral part of the instrument.

9.4.2.12 Automatic voltage regulators shall be supplied separately from all other instrument circuits and short-circuit protection only shall be provided for the voltage coils by fuses of adequate breaking capacity located as near as practicable to the source of supply.

9.4.2.13 The settings of "preference-tripping" relays shall be adjustable.

9.4.2.14 Circuit breakers for turbine-driven generators shall open automatically when the emergency overspeed switch operates.

9.4.2.15 Fuses protecting trip device circuits shall not also be used to protect any other circuit.

9.4.2.16 Excluding ground fault detection systems, voltage (potential) and current transformers shall be used for all instruments, meters, relays, control switches and other devices, which operating personnel may be in contact with so that the maximum operating voltage of the devices will not exceed 250 volts.

9.4.2.17 Current transformers used for protective devices shall not be used for any other purpose.

9.4.2.18 Nameplates for feeders and branch circuits shall include the circuit designation and the size of the fuses or circuit breaker trip calibration required for the circuit.

9.4.2.19 A voltmeter and voltmeter switch shall be provided for reading each phase voltage of the shore connection; a generator voltmeter and switch provided with suitable arrangements may be used for reading each phase voltage of the shore connection.

9.4.2.20 Where ac generators are intended for parallel operation there shall be a means provided to protect against the effects of incorrect synchronization during the parallelling process with a means provided manually to overide the the device under certain operating conditions.

9.5 SWITCHBOARD EQUIPMENT: ^

9.5.1 A. C. INSTALLATIONS

9.5.1.1 For ac generators not operated in parallel, each generator shall be provided with a frequency meter, a voltmeter and an ammeter in each phase conductor or one ammeter and one voltmeter with a selector switch for each meter designed to read the current and voltage respectively in each phase; a wattmeter shall be provided for each generator rated 50 kVA and above; the following switchgear shall be provided:

for a three-phase, three-wire insulated or a three-phase, four-wire grounded neutral system, a three-pole switch and fuse arrangement or a three-pole moulded case circuit breaker for generators under 25 kW; for generators 25 kW and above circuit breakers are to be provided in accordance with Section 10;
for a single phase, two-wire insulated or a single phase three-wire grounded neutral system, a two-pole switch and fuse arrangement or a circuit breaker as described in (a).

9.5.1.2 For ac generators operated in parallel, each generator shall be provided with a wattmeter, an ammeter with a selector switch designed to read the current in each phase and a voltmeter with a selector switch to connect the voltmeter to each phase of the generator and to one phase of the bus; suitable means shall be provided to enable one voltmeter to read shore voltage; for paralleling purposes, at least two frequency meters and a synchronizing device comprising a synchroscope and synchronizing lights shall be fitted; means for control of generator prime mover speed shall be provided at the switchboard.

9.5.1.3 For ac generators operated in parallel, suitable means shall be provided to enable one frequency meter to be connected to one phase of any one generator before the machine is connected to the bus-bars and the other frequency meter shall be permanently connected to one phase of the bus-bars.

9.5.1.4 Where ac generators are intended for operation in parallel, reverse power relays shall be provided with time-lag to prevent the tripping of circuit breakers during switching operations; the reverse power relays shall be suitable for the circumstances of reverse power between the limits of 2% and 15% of full load that may be expected according to the nature of the prime mover.

9.5.1.5 Where ac generators are installed, there shall be provided for each generator of 25 kW or over, a circuit breaker which will open simultaneously all insulated poles.

9.5.2 D.C. INSTALLATIONS

9.5.2.1 For dc generators not operated in parallel, one voltmeter and one ammeter shall be provided for each generator.

9.5..2.2 For parallel operation at least one ammeter shall be provided for each dc generator and one voltmeter, together with selector switch for measuring each generator voltage and the bus-bar voltage.

9.5.2.3 For each dc generator installed that is not arranged to run in parallel, the following switchgear shall be provided,except that fuses shall be limited as specified in subsection 4.2.9:

for a 2-wire insulated system either a double-pole circuit breaker with over-current protection in each pole, or a double-pole linked switch and a fuse in each pole;
for a 3-wire grounded system, a double-pole circuit breaker, connected to the outers, and a link connected to the neutral; and
for a 2-wire grounded system, a single-pole circuit breaker or a fuse and single-pole switch on the ungrounded pole.

9.5.2.4 For dc generators that are arranged to run in parallel, the following switchgear shall be provided:

for a 2-wire insulated system, a double-pole circuit breaker with over-current protection in each pole and reverse current protection;
for 2-wire compound-wound generators, an equalizer switch so interlocked with each circuit breaker that it must be closed before the circuit breaker and cannot be opened until the main circuit is opened;
for a 2-wire system, the reverse current protection shall be connected on the positive pole;
for a 3-wire system with the neutral wire grounded:
1. for a 3-wire shunt-wound generator, a triple-pole circuit breaker with reverse current protection, or
1. for a 3-wire shunt-wound generator, a triple-pole circuit breaker with reverse current protection, or
2. for a 3-wire compound wound generator
  1. a five-pole circuit breaker with algebraic overload protection embracing each outer and equalizer connection and algebraic reverse current protection, or
  2. a three-pole circuit breaker interlocked with a five-pole linked switch;
where reverse current protection is provided, the device shall be suitable for circumstances of reverse current between the limits of 2% and 15% of full load that may be expected according to the nature of the prime mover; and
a fall of 50% in the applied voltage shall not render the reverse current mechanism inoperative, although it may alter the amount of reverse current required to open the circuit breaker.

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