Objective Questions:

1. Fatalities have resulted from voltages as low as ___________ volts. (1)

(a). 50.

✓ (b). 30.

(c). 45.

(d). 80.

2. The central section of the main switchboard is used to house the________ (1)

✓ (a). Control gear of the main generators

(b). Auxiliary circuit switches

(c). Emergency Switchboard

(d). Pump Starters

3. The main steering gear must be able to steer the ship at maximum ahead service speed and
be capable of putting the rudder from _____ on one side to ____ on the other side in not more
than _____ secs. (1)

(a). 35⁰, 35⁰, 28

✓ (b). 35⁰, 30⁰, 28

(C). 35⁰, 30⁰, 30.

(d). 30⁰, 30⁰, 28.

4. A ship’s electrical system can be divided into ‘__________’ and ‘___________’ (1)

✓ (a). ‘supply’ and ‘users’

(b) “Generation’ and ‘Distribution’

(c). None of the above

(d). Both (a) and (b)

5. The amount of current passing through a human body depends on what two things? (1)

(a) Stress and fatigue

✓ (b) the voltage supplied by the source and the electrical resistance of your body.

(c) None of the above

(d) Both (a) and (b)

6. The voltage drop from a main switchboard to an appliance must not exceed ________ of
supply voltage.

(a) 2%

(b) 2.5%

(c) 5%

✓ (d) 6%

7. The current rating of a cable is the current that the cable can carry continuously without the
conductor exceeding ________ C with an ambient temperature of _______ C

✓ (a) 80⁰, 45⁰

(b) 75⁰, 45⁰

(c) 85⁰, 40⁰

(d) 85⁰, 45⁰

8. Class B insulation means that the device can operate upto _______ C

(a)110⁰

(b) 120⁰

✓ (c) 130⁰

(d) 145⁰

Subjective Questions:

1a. What are the safety procedures to be adopted when working on electrical installation?
(3)
1. To study the ships’ diagrams to pinpoint the location of switches and protection devices,
distribution boards and essential items of equipment. To operate and maintain equipment
according to the manufacturers’ recommendations.
2. To ensure that all guards, covers and doors are securely fitted and that all bolts and fixings are
in place.
3. Before conducting any electrical work on a ship, it is important to conduct a risk assessment to
identify potential hazards and develop appropriate safety measures. This includes identifying
electrical hazards, assessing the risk of electrical shock or electrocution, and developing a plan
to minimize or eliminate those risks.

4. To obtain a work permit prior to carrying out any work on electrical equipment. Checklists Safety
checklists can be an effective tool for ensuring that proper safety measures are followed during
electrical operations on ships. Checklists should include a list of required PPE, proper
procedures for lockout/tagout, and a list of potential hazards to be aware of.
5. To inform the Officer of the Watch before shutting down equipment for maintenance.
6. To switch off power to equipment and lock all supplies, remove fuses and store them in a safe
place.
7. To display warning notices before removing covers of equipment for maintenance.
8. To confirm that circuits are dead (by using a voltage tester) before touching conductors and
terminals. Not to rely totally on switches, etc, as sometimes they may be defective or could have
been wired or labelled wrongly, such that when indicating ‘Off, they could actually be ‘On’ thus
completing the power supply to the circuit.
9. Select and use adequately-rated test and measuring devices that are both safe for the
environment in which work is to be carried out and for the equipment too. Insulated tools and
equipment should be used when working with electrical systems to prevent electrical shock.
10. Wear Personal protective equipment (PPE) which is an essential component of electrical safety
on ships. Crew members should be provided with appropriate PPE, including insulated gloves,
safety glasses, and other protective gear. It is important to ensure that PPE is properly fitted and
used at all times when working with electrical systems and equipment.
11. Personnel working on electronic equipment should wear electrostatic discharge straps on the
wrist and ensure that the grounding connection does not hinder safe working procedures.
12. Ensure that the equipment is also grounded at a good earthing point. Don’t remove earth
(ground) connectors on power cords and within equipment.
13. Electronic components and printed circuit boards, etc, must be stored in anti-static
bags and similar storage devices.
14. To make contact with the conductors of a supposedly dead power system, first with the back of
one hand. Even if a shock should still occur, an involuntary reaction will cause the fist to be
clenched, thus moving the fingers away from the conductor - rather than involuntarily gripping
the live circuit, which has sometimes resulted in many fatalities.
15. Don’t touch live conductors under any pretext - especially when wearing damp clothing or
perspiring.
16. Don’t touch rotating parts.
17. Don’t leave live conductors or rotating parts exposed.
18. Don’t overload equipment.
19. Don’t neglect or abuse equipment.
20. In the event of an electrical accident or other emergency, it is important to have appropriate
emergency response protocols in place. This includes having trained personnel available to
respond to emergencies, as well as having appropriate first aid equipment and procedures in
place.

21. While carrying out work on high-voltage equipment it is essential that in addition to isolation of
the power supply, the system must be earthed (grounded) adequately and all residual charges
must be drained; the system must continue to be maintained at zero (ground) potential. While
working, a safe distance from other high-voltage equipment is also to be maintained. This
minimises the danger of electric shocks or flash-over bums. Safe working practices also require
 that while working in such dangerous areas, the zone must be demarcated with proper barriers
and warning signs.

1b. Write four important safety devices fitted on main switchboard. (2)

Four Important safety devices fitted on main switchboard are:

Circuit breakers: A circuit breaker is an auto shutdown device, which activates during an abnormality in
the electrical circuit. Especially during overloading or short circuit, the circuit breaker opens the supplied
circuit from MSB and protects the same. Different circuit breakers are strategically installed at various
locations on the ship.
Fuses: Fuses are mainly used for short circuit protection and comes in various ratings. If the current
passing through the circuit exceeds the safe value, the fuse material melts and isolates the MSB from
the default system. Normally, fuses are used with 1.5 times of full load current.
Over current relay: OCR is used mainly on the local panel and MSB for protection from high current. It
is installed where a low power signal is a controller. Normally relays are set equivalent to full load
current with time delay.
Dead front panel: It is also a safety device provided on the main switchboard individual panels, wherein
you cannot open the panel until the power of that panel is completely switched off.

2a. Explain with example Primary Essential Services and Secondary Essential Services (2)

Primarily Essential Services are those which need to be in continuous operation for maintaining
propulsion and steering. Some of them are as follows:
1) Steering gears.
2) Pumps for controllable pitch propellers.
3) Scavenging air blower, fuel oil supply pumps, fuel valve cooling pumps, lubricating oil pumps and
cooling water pumps for main and auxiliary engines and turbines necessary for propulsion.
4) Ventilation necessary to maintain propulsion.

Secondary Essential Services are those which need not be in continuous operation; however, they are
necessary to maintain propulsion and steering, including a minimum level of safety for
dangerous cargoes to be carried. Some of them are as follows:
1) Windlass.
2) Fuel oil transfer pumps and fuel oil treatment equipment.
3) Lubrication oil transfer pumps and lubrication oil treatment equipment
4) Pre-heaters for heavy fuel oil.
5) Starting air and control air compressors.

2b. Explain Exd Flameproof Enclosure and Exi Intrinsic Safety equipment. (3)

Exd Flameproof Enclosure

The internal apparatus may include parts which may become hot. Gas may be inside the enclosure so it
must fulfil three conditions:
1. The enclosure must be strong enough to withstand an internal explosion without suffering
damage.
2. The enclosure must prevent the flame and hot gases from being transmitted to the external
flammable atmosphere.
3. The external surface temperature of the enclosure must remain below the ignition temperature
of the surrounding gas under all operating conditions.

The transmission of flame and hot gases from a flameproof enclosure is prevented because all joints,
such as flanges, spigots, shafts and bearings are closely machined to achieve a small gap which is less
than a defined maximum. The pressure of an internal explosion is then released through the small gap
between machined faces which cools the gas sufficiently to prevent it from igniting any external
flammable atmosphere.

The maximum permitted gap depends upon three factors:

i) The type of gas with which the apparatus is safe for use. This is indicated by Apparatus Group.
ii) The width of the joint (L).
iii) The volume of the enclosure (V).

Exi Intrinsic Safety

These are circuits in which no spark nor any thermal effect produced under prescribed test conditions
(which include normal operation and specified fault conditions) is capable of causing ignition of a given
explosive atmosphere. Generally, this means limiting the circuit conditions to less than 30 V and 50 mA.
Naturally, this restricts the use of Exi protection to low power instrumentation, alarm and communication
circuits. The design of the circuit will depend on the type of gas present (gas grouping).

In the UK, two grades of intrinsic safety are recognized based on the safety factor of the equipment
involved:
1. Exia: the highest category based on a safety factor of 1.5 with two faults on the circuit.
2. Exib: based on a safety factor of 1.5 with one fault on the circuit.

In addition to apparatus in the hazardous area being rated as intrinsically safe, an electrical safety
barrier may also be fitted to the circuit. The purpose of such a barrier is to limit voltages and currents in
the hazardous area when faults occur on the circuit. A separate barrier is required for each Exi circuit
and they must be fitted outside the hazardous area.

A safety (or zener) barrier comprises:

• A fuse to limit the maximum current through the shunt (zener) diodes.
• A set of resistors to limit the maximum current into the hazardous area.
• Set of shunt connected zener diodes to limit the maximum voltage appearing on the circuit within the
hazardous area.
3a. How does a ship steering gear work? (2)

The ‘control force’ for turning is triggered off the wheel at the helm, which reaches the steering system.
The helm order or desired angle of the rudder is then transmitted from Bridge to the steering control
unit. The steering gear system then generates a torsional force at a certain scale, which is then, in turn,
transmitted to the steering gear, that rotates the rudder. A negative feedback signal of this ordered (or
desired) angle is transmitted automatically through ‘hunting gear’ to the steering gear’s control unit. This
(the negative feedback) gradually nullifies the control signal to the steering gear and causes the rudder
to stop when the desired angle has been achieved. In the case of an electro-hydraulic system it is
possible for the control unit to receive negative feedback signals through rotary transformers,
potentiometers, etc.
“Helm angle” is the position of the steering wheel relative to the midship position. The steering control
dials are normally graduated in such a manner that the rudder moves in tandem with it. For example, if
the rudder is designed to move +35°, then the control wheel will also have a fixed dial and pointer
arrangement graduated from 0° to +35°.

3b Explain the Procedure for Starting Emergency Steering Gear System. (3)

An emergency steering system, as the name suggests, is a system which is used during the
failure of the main steering system of the ship.

A situation can occur in which the remote-control operation may fail to work and there can be a
sudden loss of steering control from the bridge. This can be due to sudden power failure, any electrical
fault in the control system which includes faulty tele-motor or servo motor which is used for transferring
the signal from bridge to the steering unit.

To have control the steering of the ship at such emergency situation with manual measure from
within the steering gear room, an emergency steering system is used.

Emergency Steering Operation :

 Emergency Steering Operation.mp4

The following points should be followed for emergency steering operation.

• The procedure and diagram for operating emergency steering should be displayed in steering
gear room and bridge.
• Even in emergency situation we cannot turn the massive rudder by hand or any other means,
and that’s why a hydraulic motor is given a supply from the emergency generator directly
through emergency switch board (SOLAS regulation). It should also be displayed in the steering
room.
• Ensure a clear communication for emergency operation via VHF or ships telephone system.
• Normally a switch is given in the power supply panel of steering gear for telemotor; switch off the
supply from the panel (manual mode).
• Change the mode of operation by selecting the switch for the motor which is supplied
emergency power.
• Steer from the steering flat by operating the manipulators or similar arrangements; this will be as
effective as the NFU mode except that it is done locally and the operator may have to resort to
monitoring the rudder angle with the help of the mechanical pointer on the rudder stock itself if
the helm indicator too is not operational.

Steering gears with Push Pins:

• A Push Pin is provided which controls the flow of oil to the rams with a rudder angle
indicator.
• According to steering order, push the mechanical push pin from stbd. or port steering at the
end of the solenoid valve and keep an eye on the rudder angle indicator.

4. Explain in your own words the following: (2x5)

(a) Various Interlocks fitted to Air Circuit Breakers.

1. Drawout Cradle Rejection Hardware

To avoid the insertion of an incorrect type of circuit breaker into a drawout compartment, each
breaker and its compartment are equipped with suitable “rejection hardware.” This hardware prevents
the breaker from seating itself into the drawout rails or cubicle if it is the wrong type.

2. Racking Mechanism Interlock

The purpose of the racking mechanism interlock is to prevent the breaker from moving from the
connection position before it is in the open position. Typically, this interlock is a simple cover that must
be moved aside to gain access to the drive shaft.

3. Disconnect Position Interlock

The Disconnect Position Interlock serves to obstruct the racking screw cover from being open
when the racking mechanism is in the disconnected position.

As the cover is held open, the TRIP button becomes depressed. This ensures that the
mechanism remains in a trip-free state, preventing any contact arm movement when the closing spring
is charged by the Closing Spring Interlock.
4. Closing Spring Interlock

The closing spring interlock functions to release the closing spring as the breaker is racked out
of its housing. This eliminates the risk of a fully charged breaker discharging after being removed from
its compartment.

5. Positive Interlock

The positive interlock is located on the circuit breaker frame. Its function is to maintain the
breaker trip-free while it is being racked in or out between the connected and test positions.

6. Padlocks

Provisions are made on all circuit breakers to use padlocks to prevent the breaker from being
closed. Padlock shackles are usually inserted through the trip button or racking screw cover. In either
case, the shackle holds the trip button, keeping the mechanism trip-free.

7. Key and Door Interlock

Optional interlocks include key interlocks and door interlocks. The function of the key interlock is
to prevent an open breaker from being closed when the lock bolt is extended, and its key is removed.

(b) Why the axes of a rotating machine should not be placed athwart ships unless so
designed? What precautions to be taken they have to installed athwartship?
In order, to reduce end-play and avoid hammering during rolling, machines should be instated,
with their axis of rotation either vertical or in the fore and aft direction.
If they unavoidably have to be placed athwartship, care must be taken to reduce the end-play
and to provide suitable thrust bearings to prevent any hammering action when the ship rolls.

(c) The principle of the various types of closing mechanism of circuit breakers.
Rapid closing of the breaker helps to prevent damage and most are power, rather than
manually, closed. Various types of closing mechanisms may be fitted:
(a) Independent manual spring - The spring charge is directly applied by manual depression of
the closing handle. The last few centimetres of handle movement release the spring to close the
‘breaker*. Closing speed is fast and independent of the operator.
(b) Motor-wound stored-charge spring - The closing spring is charged by a motor / gearbox unit.
Spring recharging is automatic, following closure of the ‘breaker’. Breaker closure is operated by a push
button. This may be a direct mechanical release of the charged spring or it may initiate an electrical
release via a solenoid-operated latch. After the operation of a spring-activated breaker, the motor can
usually be heard Charging the spring for the next time.

(d) What is electrical shock?

Simultaneous contact between the body’s surface and two electrical conductors at different
potentials, and the physiological consequences of this contact is a shock. Electric shock is often from
hand to foot or from hand to hand. The two conductors may be a hot (live) conductor and the ground or
two hot (live) conductors as in two of the phase wires of a three-phase power distribution system. The
severity of the consequences of electric shock depends on a variety of factors. The physiological effects
of electric shock are not produced by electric potential i.e., voltage, but rather by the electric current that
is driven by the potential difference, which is applied externally to the body surface. The combined
effective electrical resistance of the body volume involved and the intimacy i.e., the surface area
involved and pressure applied during skin-conductor contact, have a major effect on the severity of the
electric shock.

(e) State the angles of heel and trim at which machinery should be capable of operating.
Main propulsion and all auxiliary machinery essential to the ship shall, as fitted in the ship, be
designed to operate when the ship is upright and when inclined at any angle of list up to and including
15°either way under static conditions; and 22.5° under dynamic conditions (rolling) either way and when
simultaneously inclined dynamically (pitching) 7.5° by bow or stem.
The emergency generator and its prime mover and any emergency accumulator battery shall be
so designed and arranged as to ensure that they will function at full rated power when the ship is
upright and when inclined at any angle of list up to 22.5° or when inclined up to 10° either in the fore or
aft direction or is in any combination of angles within those limits.

5. Define the terms Insulation Resistance and Dielectric Strength. (2)

Insulation Resistance is the resistance to current leakage through the insulation material expressed in
Ohms. Insulation resistance cane be measured by Megger without damaging the insulation. Observed
resistance indicates general condition of insulation but does not guide to any localised fault (eg. Clean
dry insulation having cracks). Megger testing is a non-destructive test, could be carried out without
damaging the insulation.
Dielectric Strength is the ability of insulating material to withstand potential difference. It is usually
expressed in terms of voltage at which insulation fails because of electrostatic stress. Dielectric strength
of a material can be measured by raising voltage across a test sample until the insulation breaks down.
This is a destructive test as during testing cable insulation is damaged.

6. What is lamp efficacy? (2)

Lamp efficacy also called luminous efficiency is defined as ratio of lumens / watt. For
example 100 watt Single coil type incandescent lamp with a average light output 1160 lumens
has efficacy 11.6 lumens/watt

8a. What is meaning of the term flame retardant? (2)

Flame retardant means the material concerned should be able to slow down or cease
propagation of flame, but it will not prevent onset of fire.
For electric cable this is tested by holding a 4 ft long cable vertically and put on fire at the bottom
with a flame of known strength.
 1. If the flame travels to full length of cable, then cable is graded as ‘flame extending’
2. If the flame is extinguished before it reaches top, it is classified as flame retardant.
3. A flame-retardant cable must be able to resist the flame, and also after cooling, be able
to withstand an AC voltage of twice the rated voltage for 1 minute.

8b. How to recover insulation resistance of cable exposed to moisture? (3)

Exposed cables (e.g. for deck lighting) may develop a low insulation due to ingress of moisture.
‘Wet’ cables can be dried out by injecting a heating current from a current injection set or a welding
transformer set.
Care should be taken not to overheat the cables which could cause further damage. The cable
should be disconnected at both ends from equipment and connected as shown in below fig. The
injection cables must have good connections at each end. Current flow and cable temperature should
be carefully monitored. When satisfactory insulation values have been restored, a final check should be
made with the cable at normal ambient temperature.

The injected heating current must never exceed the rated current for the cable. Am ammeter
could be used for monitoring. Start at the lowest available setting on the injection set. The voltage
should be in the region of 30-55 V depending on the current setting. The cable temperature can be
monitored an infra-red sensor and should not be allowed to exceed a temperature rise of 30⁰ C.

Temperature and insulation resistance should be recorded every hour. When the insulation
resistance becomes steady, heating should be carried for a further 4 hours. Final reading of atleast 20
MOhm to earth and 100 MOhm between cores to be expected.