Thursday, February 11, 2010
Earthing_system
Earthing_system
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In electricity supply systems, an earthing system defines the electrical potential of the conductors relative to that of the Earth's conductive surface. The choice of earthing system has implications for the safety and electromagnetic compatibility of the power supply. Note that regulations for earthing (grounding) systems vary considerably among different countries.
A protective earth (PE) connection ensures that all exposed conductive surfaces are at the same electrical potential as the surface of the Earth, to avoid the risk of electrical shock if a person touches a device in which an insulation fault has occurred. It ensures that in the case of an insulation fault (a "short circuit"), a very high current flows, which will trigger an overcurrent protection device (fuse, circuit breaker) that disconnects the power supply.
A functional earth connection serves a purpose other than providing protection against electrical shock. In contrast to a protective earth connection, a functional earth connection may carry a current during the normal operation of a device. Functional earth connections may be required by devices such as surge suppression and electromagnetic interference filters, some types of antennas and various measurement instruments. Generally the protective earth is also used as a functional earth, though this requires care in some situations.
Contents
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[edit] IEC terminology
International standard IEC 60364 distinguishes three families of earthing arrangements, using the two-letter codes TN, TT, and IT.
The first letter indicates the connection between earth and the power-supply equipment (generator or transformer):
| T | : | direct connection of a point with earth (Latin: terra); |
| I | : | no point is connected with earth (isolation), except perhaps via a high impedance. |
The second letter indicates the connection between earth and the electrical device being supplied:
| T | : | direct connection of a point with earth |
| N | : | direct connection to neutral at the origin of installation, which is connected to the earth |
[edit] TN networks
In a TN earthing system, one of the points in the generator or transformer is connected with earth, usually the star point in a three-phase system. The body of the electrical device is connected with earth via this earth connection at the transformer.
The conductor that connects the exposed metallic parts of the consumer is called protective earth (PE). The conductor that connects to the star point in a three-phase system, or that carries the return current in a single-phase system, is called neutral (N). Three variants of TN systems are distinguished:
| TN?S | : | PE and N are separate conductors that are connected together only near the power source. |
| TN?C | : | A combined PEN conductor fulfills the functions of both a PE and an N conductor. The combined PEN conductor typically occurs between the substation and the entry point into the building, whereas within the building separate PE and N conductors are used. In the UK, this system is also known as protective multiple earthing (PME), because of the practice of connecting the combined neutral-and-earth conductor to real earth at many locations, to reduce the risk of broken neutrals - with a similar system in Australia being designated as multiple earthed neutral (MEN). |
| TN?C?S | : | Part of the system uses a combined PEN conductor, which is at some point split up into separate PE and N lines. |
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| TN-S: separate protective earth (PE) and neutral (N) conductors from transformer to consuming device, which are not connected together at any point after the building distribution point. | TN-C: combined PE and N conductor all the way from the transformer to the consuming device. | TN-C-S earthing system: combined PEN conductor from transformer to building distribution point, but separate PE and N conductors in fixed indoor wiring and flexible power cords. |
It is possible to have both TN-S and TN-C-S supplies from the same transformer. For example, the sheaths on some underground cables corrode and stop providing good earth connections, and so homes where "bad earths" are found get converted to TN-C-S.
[edit] TT network
In a TT earthing system, the protective earth connection of the consumer is provided by a local connection to earth, independent of any earth connection at the generator.
The big advantage of the TT earthing system is the fact that its clear of high and low frequency noises that come through the neutral wire from various electrical equipment connected to it. This is why TT has always been preferable for special applications like telecommunication sites that benefit from the interference-free earthing. Also, TT does not have the risk of a broken neutral.
In pre-RCD era, the TT earthing system was unattractive for general use because of its worse capability of accepting high currents in case of a live-to-PE short circuit (in comparison with TN systems). But as residual current devices mitigate this disadvantage, the TT earthing system becomes attractive for premises where all AC power circuits are RCD-protected.
[edit] IT network
In an IT network, the distribution system has no connection to earth at all, or it has only a high impedance connection. In such systems, an insulation monitoring device is used to monitor the impedance
[edit] Other terminologies
While the national wiring regulations for buildings of many countries follow the IEC 60364 terminology.In North America (United States and Canada), the term "equipment grounding conductor" refers to equipment grounds and ground wires on branch circuits, and "grounding electrode conductor" is used for conductors bonding an earth ground rod (or similar) to a service panel. "Grounded conductor" is the system "neutral".
[edit] Properties
[edit] Cost
- TN networks save the cost of a low-impedance earth connection at the site of each consumer. Such a connection (a buried metal structure) is required to provide protective earth in IT and TT systems.
- TN-C networks save the cost of an additional conductor needed for separate N and PE connections. However, to mitigate the risk of broken neutrals, special cable types and lots of connections to earth are needed.
- TT networks require proper RCD protection.
[edit] Fault path impedance
If the fault path between accidentally energized objects and the supply connection has low impedance, the fault current will be so large that the circuit overcurrent protection device (fuse or circuit breaker) will open to clear the ground fault. Where the earthing system does not provide a low-impedance metallic conductor between equipment enclosures and supply return (such as in a TT separately-earthed system), fault currents are smaller, and will not necessarily operate the overcurrent protection device. In such case a residual current detector is installed to detect the current leaking to ground and interrupt the circuit.
[edit] Safety
- In TN, an insulation fault is very likely to lead to a high short-circuit current that will trigger an overcurrent circuit-breaker or fuse and disconnect the L conductors. With TT systems, the earth fault loop impedance can be too high to do this, or too high to do it quickly, so an RCD (or formerly ELCB) is usually employed. The provision of a Residual-current device (RCD) or ELCB to ensure safe disconnection makes these installations EEBAD (Earthed Equipotential Bonding and Automatic Disconnection).
- Many 1950s and earlier earlier TT installations in the UK may lack this important safety feature. Non-EEBAD installations are capable of the whole installation CPC (Circuit Protective Conductor) remaining live for extended periods under fault conditions, which is a real danger.
- In TN-S and TT systems (and in TN-C-S beyond the point of the split), a residual-current device can be used as an additional protection. In the absence of any insulation fault in the consumer device, the equation IL1+IL2+IL3+IN = 0 holds, and an RCD can disconnect the supply as soon as this sum reaches a threshold (typically 10-500 mA). An insulation fault between either L or N and PE will trigger an RCD with high probability.
- In IT and TN-C networks, residual current devices are far less likely to detect an insulation fault. In a TN-C system, they would also be very vulnerable to unwanted triggering from contact between earth conductors of circuits on different RCDs or with real ground, thus making their use impracticable. Also, RCDs usually isolate the neutral core. Since it is unsafe to do this in a TN-C system, RCDs on TN-C should be wired to only interrupt the live conductor.
- In single-ended single-phase systems where the Earth and neutral are combined (TN-C, and the part of TN-C-S systems which uses a combined neutral and earth core), if there is a contact problem in the PEN conductor, then all parts of the earthing system beyond the break will rise to the potential of the L conductor. In an unbalanced multi-phase system, the potential of the earthing system will move towards that of the most loaded live conductor. Therefore, TN-C connections must not go across plug/socket connections or flexible cables, where there is a higher probability of contact problems than with fixed wiring. There is also a risk if a cable is damaged, which can be mitigated by the use of concentric cable construction and/or multiple earth electrodes. Due to the (small) risks of the lost neutral, use of TN-C-S supplies is banned for caravans and boats in the UK, and it is often recommended to make outdoor wiring TT with a separate earth electrode.
- In IT systems, a single insulation fault is unlikely to cause dangerous currents to flow through a human body in contact with earth, because no low-impedance circuit exists for such a current to flow. However, a first insulation fault can effectively turn an IT system into a TN system, and then a second insulation fault can lead to dangerous body currents. Worse, in a multi-phase system, if one of the live conductors made contact with earth, it would cause the other phase cores to rise to the phase-phase voltage relative to earth rather than the phase-neutral voltage. IT systems also experience larger transient overvoltages than other systems.
- In TN-C and TN-C-S systems, any connection between the combined neutral-and-earth core and the body of the earth could end up carrying significant current under normal conditions, and could carry even more under a broken neutral situation. Therefore, main equipotential bonding conductors must be sized with this in mind; use of TN-C-S is inadvisable in situations such as petrol stations, where there is a combination of lots of buried metalwork and explosive gases.
[edit] Electromagnetic compatibility
- In TN-S and TT systems, the consumer has a low-noise connection to earth, which does not suffer from the voltage that appears on the N conductor as a result of the return currents and the impedance of that conductor. This is of particular importance with some types of telecommunication and measurement equipment.
- In TT systems, each consumer has its own connection to earth, and will not notice any currents that may be caused by other consumers on a shared PE line.
[edit] Regulations
- In the United States National Electrical Code and Canadian Electrical Code the feed from the distribution transformer uses a combined neutral and grounding conductor, but within the structure separate neutral and protective earth conductors are used (TN-C-S). The neutral must be connected to the earth (ground) conductor only on the supply side of the customer's disconnecting switch. Additional connections of neutral to ground within the customer's wiring are prohibited.
- In Argentina, France (TT) and Australia (TN-C-S), the customers must provide their own ground connections.
- Japan is governed by PSE law.
[edit] Application examples
- Most modern homes in Europe have a TN-C-S earthing system. The combined neutral and earth occurs between the nearest transformer substation and the service cut out (the fuse before the meter). After this, separate earth and neutral cores are used in all the internal wiring.
- Older urban and suburban homes in the UK tend to have TN-S supplies, with the earth connection delivered through the lead sheath of the underground lead-and-paper cable.
- Some older homes, especially those built before the invention of residual-current circuit breakers and wired home area networks, use an in-house TN-C arrangement. This is no longer recommended practice.
- Laboratory rooms, medical facilities, construction sites, repair workshops, mobile electrical installations, and other environments that are supplied via engine-generators where there is an increased risk of insulation faults, often use an IT earthing arrangement supplied from isolation transformers. To mitigate the two-fault issues with IT systems, the isolation transformers should supply only a small number of loads each and/or should be protected with an insulation monitoring device (generally used only by medical, railway or military IT systems, because of cost).
- In remote areas, where the cost of an additional PE conductor outweighs the cost of a local earth connection, TT networks are commonly used in some countries, especially in older properties. TT supplies to individual properties are also seen in mostly TN-C-S systems where an individual property is considered unsuitable for TN-C-S supply.
- In Australia, the TN-C-S system is in use; however, the wiring rules currently state that, in addition, each customer must provide a separate connection to earth via both a water pipe bond (if metallic water pipes enter the consumer's premises) and a dedicated earth electrode. In older installations, it is not uncommon to find only the water pipe bond, and it is allowed to remain as such, but the additional earth electrode must be installed if any upgrade work is done. The protective earth and neutral conductors are combined until the consumer's neutral link (located on the customer's side of the electricity meter's neutral connection) - beyond this point, the protective earth and neutral conductors are separate.
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An Emergency Power System
An Emergency Power System
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An emergency power system tackles all emergency conditions on ship by providing an uninterrupted supply of power.To ensure safety on ship utmost priority should be given to back up power sources and generators. Lets learn what does this emergency power system comprises of and stands for?
The Story Continues
You have read about a few basics of marine electrical systems including generators, motors and switchboards. As you now find yourself enlightened with the brief gist of the crucial elements of the ship’s electrical system, you decide to take a quick coffee break and munch on a bar of snickers, simultaneously trying to recollect and imbibe whatever you have learnt so far:
The generator is the heart of the ship. To control and use the generator we use motors, motor controls and main switch boards.
Now, these elements constitute the basic requirement of the electrical system of any kind of ship. But that doesn’t mean that the ship can run solely on them. There are few other elements and parameters that need to be taken into consideration for the continuous supply of electrical power and also to ensure safety and redundancy. Let’s learn a bit more about them.
Emergency Power System
The main intention of an emergency power system is to furnish immediate, automatic electric power to a limited number of selected vital circuits. The emergency power system includes one or more diesel-driven emergency generators (which we will learn a bit more on later) as well as an emergency switch board and a distributed system. Both emergency generator and emergency switch board are kept above the waterline to minimize danger from flooding. Emergency services also include the navigation, safety and emergency lights.
All these emergency services should be supplied from the emergency switch board. An emergency switch board has distributed panels for all the emergency services onboard. The emergency switch board as we discussed earlier is always located above the bulkhead deck. This is to ensure that at the time of any emergency such as fire or flooding, the switchboard is not affected and is easily accessible and that any such emergency does not lead to loss of lighting in escape routes and other important navigation control areas.
Thus as of now, the main components of an emergency power system are a generator and switch board.
Safety: An integral part.
The ship’s emergency electrical system and the safety of the ship and the crew are interwoven. You can say that the electrical emergency services, also known as the “emergency power system”, is the back-bone of safety on the ship.
The arrangement and the installation of the emergency services should be so smartly done that no matter what happens to the ship the emergency system should provide energy and support lives on ship until the situation can be handled.
Firstly, let us find out what does it mean by emergency power system or emergency services?
Emergency power system
The main intention of emergency power system is to furnish immediate, automatic source of electric power to limited number of selected vital circuits. The emergency power system includes one or more diesel driven emergency generator, which we will learn a bit more on later, emergency switch board and a distributed system. Both emergency generator and emergency switch board are kept above the waterline, to minimize danger from flooding. Emergency services also include the navigation, safety and emergency lights.
All these emergency services should be supplied from the emergency switch board. Emergency switch board has distributed panels for all the emergency services onboard. Emergency switch board as we discussed earlier is always located above the bulkhead deck. This is to ensure that at the time of any emergency such as fire or flooding, the switchboard is not affected and is easily accessible and that any such emergency does not lead to loss of lightening in escape routes and other important navigation control areas.
Thus the main components of an emergency power system are : Emergency generator and emergency lights.
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Emergency generator
“Black out” is a condition considered similar to a “dead ship” condition. It is a condition under which the main propulsion plant, boilers and auxiliaries are not in operation and also there is no stored energy available to restore them. This is the time for the emergency generator to take over. The emergency generator has its own prime mover and fuel supply.
As the ship’s emergency generator takes over the battle functions as soon as the main power fails, utmost care should be taken at the time of installation. It’s of extreme importance that load on the generator is at the top of the priority list while considering the factors affecting. This is because when there is a sudden transfer of load from the main generators to the emergency generator there is a high chance of the later getting overloaded. Thus the emergency generators should be of the capacity same as the main generators capacity. To equalize the capacity requirement of the emergency generator to the main generator generally more then one emergency generator should be made available.
Emergency lights
These lighting fixtures must provide an uninterrupted source of lighting in the event of power outage. The source of power for these lighting shall consist of accumulator batteries which are continuously charged from the main switch board. All these lights should operate at least for three hours.
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ship electrical standards...distribution
ship electrical standards...distribution
11.1 In passenger ships, distribution systems shall be so arranged that fire in any main fire zone will not interfere with essential services in any other main fire zone.
11.2 The requirement of subsection 11.1 is met if the main and emergency feeders passing through any zone are separated both vertically and horizontally as widely as is practicable.
11.3 If, in any passenger ship, two or more generating sets can be in operation at the same time for maintaining the auxiliary services essential for the propulsion or safety of the ship:
- provision shall be made for the sets to operate in parallel; and
- means shall be provided so that in the event of overload or a partial failure of the supply, the services not essential to the propulsion and safety of the ship will be cut out first, the services essential for those purposes being retained in circuit with such of the generators as may remain in service.
11.4 Distribution systems employing a single wire with hull return shall not be used for power, heating or lighting; this does not preclude the use of impressed current cathodic protective systems, limited and locally grounded systems, or insulation level monitoring devices where the circulating current is less than 30 mA.
11.5 Every current-consuming appliance shall be connected to either:
- a main switchboard;
- an emergency switchboard;
- a distribution centre; or
- a panelboard;
11.6 Each branch circuit shall be protected against short-circuit and, subject to subsection 11.10, shall also be protected against overload.
11.7 Each branch circuit operating at voltages of 55 volts or over shall be provided with a switch or circuit breaker with a pole for each conductor; any switch or circuit breaker fitted shall operate simultaneously in the grounded conductor and the insulated conductor.
11.8 No fuse, non-linked switch or non-linked circuit breaker shall be inserted in a grounded conductor.
11.9 Each circuit shall be permanently indicated together with the rating or setting of the appropriate overload protective device.
11.10 Where the steering gear is operated by two independent electrically powered mechanisms and an approved alternative means of steering is not provided, two independent sets of supply cables shall be provided which shall be:
- connected to the main switchboard, except that where there is an emergency generator, one set shall be connected to the main switchboard via the emergency switchboard, in accordance with the requirements of the Marine Machinery Regulations Schedule (VII),
- Separated throughout their length as widely as practicable,
- Together with the motors, protected by fuses, circuit breakers or other similar devices against short-circuit; no other overload device or fuse that will open the steering motor power circuit is to be provided in the motor control circuit and the steering control circuits to the bridge; and
- Short circuit protection only shall be provided for the control circuits of the bridge steering control systems; the protection shall be instantaneous and rated at 300 percent of the current carrying capacity of the smallest control system conductor.
11.11 Each steering gear motor starter shall be equipped with a thermal overcurrent relay that shall operate an alarm when the motor is overloaded.
11.12 Each steering gear motor is to be provided with the following monitoring devices at the main machinery control position and at the steering control station on the bridge:
- running and stop indication for each steering gear motor;
- audible alarm and visual lamp indication for the following:
- overcurrent,
- main power supply failure;
- control power failure;
- where a steering gear hydraulic fluid reservoir is fitted it shall be provided with a low level alarm,
- phase failure alarm on the load side of the starter.
- dimming devices may be fitted in accordance with section 3 (23),
- remote steering control stations shall include items (a) and (b); the audible device may be omitted if the bridge alarm can be heard at the remote steering positions.
11.13 The supply for each steering gear remote control system shall have its own individual circuit supplied from the respective steering gear power circuit, or directly from the switchboard busbars adjacent to the steering gear power circuit in addition the steering gear power circuit shall also supply each of the monitoring devices required in Section 11.12 (a) and (b).
11.14 Where the steering gear is electrically operated by remote control from the bridge, or from other remote steering control stations there shall be provided two independent electric control systems.
11.15 Where fitted, “jog” steering control handles shall be of a type that requires a positive action to initiate operation.
11.16 The control of each steering gear motor is to be such that the motor will restart automatically upon restoration of voltage after a power failure.
11.17 Means shall be provided to effectively communicate between the bridge and steering gear compartment.
11.18 Steering gear motors are to be controlled from the bridge, the steering gear compartment; control may also be provided at other control stations; however when control from more than one position is provided, the over-riding control shall be at the bridge while the vessel is under way.
11.19 Machinery space ventilation fans, boiler fans, fuel oil transfer pumps, fuel oil pressure pumps and lube oil transfer and purifiers shall be provided with a means for stopping from a position outside the machinery space which will always be accessible in the event of fire in the space, in passenger vessels the accommodation and vehicular ventilation fans shall be provided with a means of stopping and motor indication at the main fire control station.
11.20 The emergency means for stopping machinery space ventilation fans, accommodation ventilation fans and vehicular space ventilation fans shall be separate and completely independent of each other.
11.21 The means provided for remote stopping of the electrical equipment required by subsection 11.19 shall be so arranged that a separate power source is not required to accomplish remote emergency stopping; the source of power provided in order to accomplish remote emergency stopping shall be:
- provided from each individual motor control circuit; or
- from a dedicated source of power feeding an individual motor, or group of motors connected to a motor control centre for a particular space, shunt trip arrangements shall not be permitted.
11.22 The activation of a remote emergency stop circuit, manually initiated, shall continue until it is manually reset.
11.23 Together with the manually initiated stopping devices for the galley ventilation fans located in the galley, the range/fryer gas smothering system shall also initiate a galley ventilation shut down
11.24 Where refrigerated lockers of the walk-in type can be locked so that they cannot be opened from inside, a “locked-in” alarm system shall be provided and shall comprise:
- an on-off switch located inside at the exit of each such space,
- a visual and audible alarm located in the galley or other space where persons are normally present or employed; and
- a nameplate for both the actuator and the alarm to designate the function.
11.25 A branch circuit having a current rating not exceeding 15 amps may supply any number of lighting points; the total connected load of the sub-circuit shall not exceed 80% of the set current of the final sub-circuit protective device unless the final sub-circuit protective device is certified and marked for continuous operation at 100% of its rating.
11.26 When the total connected load is not known, a branch circuit having a current rating not exceeding 15 amps may supply any number of lighting points up to the following maxima:
- at voltages up to and including 50V-10 points;
- from 51V up to and including 130V-14 points; or
- from 131V up to and including 230V-18 points.
11.27 A branch circuit of rating exceeding 20 amperes is not to supply more than one point.
11.28 Where two or more distribution panels or panel-boards are connected to a cable and the cable is looped from board to board without passing through a protective device, the cable conductors shall be of the same cross-sectional area throughout except where the length between panels is less than 2 metres.
11.29 Where an automatic sprinkler system is installed in accordance with the Fire Detection and Extinguishing Equipment Regulations:
- there shall be not less than two independent sources of power supply for the sprinkler seawater pump and automatic alarm and detection system,
- one supply for the pump shall be taken from the main switchboard and one from the emergency switchboard by separate feeders reserved solely for that purpose,
- the feeders shall be arranged so as to avoid galleys, machinery spaces and other enclosed spaces of high fire risk except insofar as it is necessary to reach the appropriate switchboards and shall be run to an automatic change-over switch situated near the sprinkler pump; this switch shall permit the supply of power from the main switchboard so long as a supply is available therefrom and be so designed that, upon failure of that supply, it will automatically change-over to the supply from the emergency switchboard;
- the switches on the main switchboard and the emergency switchboard shall be clearly labelled and normally kept closed; no other switch shall be permitted in the feeders concerned; and
- one of the sources of power supply for the alarm and detection system shall be an emergency source.
11.30 Where an automatic fire alarm and fire detection system is required the system shall be in accordance with Section 21.6.
11.31 Separate branch circuits shall be provided for every motor required for an essential service and for every motor rated at 1.25 kW or more.
11.32 Lighting circuits shall be supplied by branch circuits separate from those for heating and for power requirements; this does not preclude the supply from lighting circuits of cabin ventilating fans, wardrobe heaters, anti-condensation heaters or small power consumers up to 600 watts.
11.33 If a ship is divided into fire zones, at least two separate circuits for lighting shall be provided in each zone, one of which may be the circuit for the emergency lighting.
11.34 A lighting circuit in a bunker or hold shall be provided with an isolating switch and visual indication outside the space which shall be accessible only to authorized personnel and provision shall be made for the complete isolation and locking in the “off” position of the means of control of every such circuit.
11.35 Electric lighting in main propelling machinery spaces, other large machinery spaces and on passenger ships, in alleyways and stairways leading to boat decks and in public rooms shall be supplied from at least two final sub-circuits, one of which may be the emergency circuit, in such a way that failure of any one of the circuits does not reduce the lighting to an inadequate level; lighting circuits shall be arranged so as to provide an adequate level of illumination on the fronts of switchboards and control panels; circuits and fittings for this purpose may form an integral part of the switchboard or control panel.
11.36 Where single-phase ac branch circuits are connected into three-phase or three-phase, 4-wire or single-phase, 3-wire distribution panels, the circuits shall be so disposed that the load will be balanced within 15% at the individual distribution panel; for dc branch circuits connected into 3 wire dc distribution panels, the circuits shall be similarly arranged.
11.37 Navigation lights shall be connected by means of a length of heavy duty flexible cable to a watertight receptacle outlet located adjacent thereto and each lamp shall be connected to it’s branch circuit conductors by means of an individual heavy duty portable cable and a watertight receptacle plug or may be wired direct:
- electric side, masthead, anchor and stern lights shall be controlled by an indicator panel located in an accessible position under the control of the officer of the watch;
- each such light shall be controlled and protected in each insulated pole by a switch and fuses or circuit breaker mounted on the indicator panel referred to in paragraph (a),
- each such light shall be provided with an automatic indicator which gives aural or visual warning, or both, in the event of extinction of the light and if:
- an aural device alone is used, shall be connected to a separate source of supply; or
- a visual signal is used which is connected in series with the light, means shall be provided to prevent the extinction of the light due to the failure of the visual signal,
- on small vessels where the condition of the navigation light can be observed from the manoeuvring position automatic failure of the lamp indicator need not be fitted.
- for vessels 15 metres or greater the indication light panel shall be provided with a means to transfer a navigation light to the respective alternate lamp by means of a suitable selector switch located in the indicator panel;
- provision shall be made on the bridge to select an alternative main supply circuit by means of a transfer switch located at the indicator panel,
- the feeders supplying a navigation light panel shall be protected by over-current devices rated or set at not less than twice the rating of the line protection in the navigation light panel: the navigation panel shall be fitted with main over-current devices rated or set greater than the maximum load including spares of the panel for each feeder and with branch protection rated or set at not less than 3 amperes in each conductor, for voltages under 55 volts refer to section 51.7; and
- the period of time required for the alternate supply to the navigation lights control panel shall be in accordance with the applicable group in Schedule 1.
11.38 The wiring between the indicator panel and the watertight duplex receptacle at the side, masthead, anchor and stern lights shall be in duplicate and may be either two, 2-conductor cables or one 4-conductor cable.
11.39 Where arrangements are made for the supply of electric power from an external source on shore or elsewhere, a suitable connection box shall be installed in a position in the ship suitable for the convenient reception of flexible cables from the external source, having terminals of ample size and suitable shape to facilitate a satisfactory connection:
- except for single-phase shore power arrangements fitted in accordance with paragraph (e), all shore power connections shall be provided with a ground connection terminal for connecting the vessel’s hull to the shore ground,
- the shore connection shall be provided with an indicator at the main switchboard in order to show when the cable is energized,
- means shall be provided for checking the polarity for dc and single-phase ac systems and the phase sequence for three-phase ac of the incoming supply in relation to the ship’s system; and
- bolts, nuts and washers used to maintain contact on bus and connection bars shall be of non-ferrous material or of steel rendered corrosion-resistant by zinc-electroplating or an equivalent process,
- for vessels that may experience excessive induced electrolysis as a result of a shore power installation fitted in accordance with paragraph (a), an alternative shore power connection arrangement may be fitted as follows:
- provided with an isolating transformer that has the transformer case electrically isolated from the transformer core,
- the isolating transformer case grounded to the vessel’s hull or to the continuous ground conductor for vessels constructed of wood or composite materials,
- the exterior of the shore power cable connection plug on the vessel must be effectively encapsulated and insulated; and
- a series of sketches, depicted in figures 11-1 and 11-2 are provided for reference.
11.40 Vessels that utilize a grounded distribution system are to be provided with a suitable means to prevent the flow of load current through the hull or the grounding hardware while connected to shore power facilities.
11.41 Transformers for power and lighting shall be protected in accordance with Section 26, Part I of the Canadian Electrical Code.
11.42 Automatic changeover switches, relays and circuit breakers shall not be operated by a separate, remote or auxiliary power source.
11.43 Magnetic switches used for automatic bus transfer shall be of the latched type with coils energized only at the moment of operation.
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