Electrical General — Most Asked Questions
30 questions asked about electrical general across the General and Fn 5 papers, heaviest first.
Learn the system first
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1 types of transformer??
Answer
Transformers move voltage up or down by turns ratio; ships use step-down daily, with auto and instrument types for starting and metering.
- Step-up: secondary turns more than primary — voltage rises on the output side.
- Step-down: secondary turns fewer — the ship’s daily type for lighting and control supplies.
- Construction families: core, shell and berry types describing how core and windings wrap each other.
- Special duty: autotransformers for reduced-voltage motor starting and instrument transformers (current and potential) for meters and protection.
Surveyor follow-up: lighting transformer hums hot with voltage low on one phase — winding or supply, and what do you megger first?
Full theory: Transformers, Diodes & Thyristors -
2 Losses in transformer
Also asked: “losses in transformer and formula”, “Losses in transformer and reasons”, “Different losses in transformer?”
Answer
Transformer losses are copper in the windings and iron in the core — one grows with load, the other stays constant.
- Copper loss in primary and secondary windings rises with the square of load current.
- Iron loss splits into hysteresis from flipping magnetism and eddy currents circulating in the core steel.
- Laminated cores choke eddy currents; good steel and tight joints cut hysteresis.
- Efficiency is output over output plus both losses — test open-circuit for iron loss and short-circuit for copper loss.
Surveyor follow-up: transformer hot at no load with normal voltage — copper or iron loss, and which test proves it?
Full theory: Transformers, Diodes & Thyristors -
3 Single phasing of motor?
Also asked: “What is single phasing. Will motor restart under single phasing”, “Motor single phasing. And how would you check single phasing”, “problem with motor (single phasing”
Answer
Single-phasing is a motor running on two legs: it hums loud, vibrates, overheats and dies unless protection stops it.
- A lost phase breaks the symmetry — the motor hums louder than normal and shakes instead of spinning cleanly.
- It draws excess current on the healthy phases, smells of hot insulation and can smoke from the casing.
- Causes live upstream: loose wire, bad contactor, failed overload relay, blown fuse or open breaker pole.
- Confirmed single-phasing means stop at once, start the standby, then megger windings and earth continuity before any test run.
Surveyor follow-up: the motor will not restart after tripping on single phase — supply or winding, and what do you check first?
Full theory: Induction Motors — Principle, Faults & Testing -
4 intrinsically safe equipment
Also asked: “Intr safe equipment”
Answer
Intrinsically safe gear cannot spark an explosion: barriers cap its energy so faults in the safe area never reach the hazardous one.
- Each Exi circuit gets its own safety barrier outside the hazardous space.
- The zener barrier stacks a fuse, current-limiting resistors and shunt zener diodes to clamp voltage and current.
- Apparatus in the hazardous area is rated Exi to match — ordinary gear, however small, is forbidden.
- Prove barriers, earths and labels before entering gas-dangerous spaces with live instruments.
Surveyor follow-up: multimeter for the pump room — ordinary, flameproof or intrinsically safe, and what barrier proves it?
Full theory: Instruments & Safety Systems -
5 what is auto transformer ?
Also asked: “Auto transformer where in used”, “Difference b/w transformer and auto”
Answer
An autotransformer is one winding doing two jobs: part shared by primary and secondary, tapped for reduced-voltage starting.
- Single winding with a tap — no electrical isolation between input and output, unlike a two-winding transformer.
- Cheaper, smaller and lighter than an equivalent double-wound unit for the same starting duty.
- Best answer for big-motor starts like bow thrusters: deep surge cut with the least torque sacrifice.
- Trade-off is the missing isolation — downstream faults and voltages reflect straight back to the mains.
Surveyor follow-up: autotransformer or star-delta for a 300 kW thruster — which one, and what decides?
Full theory: Transformers, Diodes & Thyristors -
6 Speed control of Motor
Also asked: “How is speed of motors controlled”
Answer
Motor speed follows frequency, poles or slip: VFD for smooth control, pole-change for steps, rotor resistance for wound rotors under load.
- VFD varies voltage with frequency from zero to rated and beyond for full torque-speed control.
- Pole-change reconnects star-delta style windings for fixed speed steps on deck and fan motors.
- Wound-rotor resistance reinserted under heavy load drags slip toward 25% for slow running.
- Pick by duty: VFD for pumps and fans that throttle, pole-change for winches with fixed speeds.
Surveyor follow-up: fan too fast on VFD minimum with dampers shut — drive, motor or system, and what do you change?
Full theory: Induction Motors — Principle, Faults & Testing -
7 What to check before shore connection?
Also asked: “what all checks are carried out while connecting shore connection??”
Answer
Prove shore power matches the ship before closing: isolation healthy, sequence right, voltage sound, hull earthed.
- Isolation switch, fuses and breaker proved working with the connection box terminals and hull earth made fast.
- Phase-sequence indicator proved with voltmeter reading correct volts and rotation.
- Ship alternators shut down first so no paralleling across different sources.
- Test supply dead-to-live in order — never trust shore breakers without your own meter.
Surveyor follow-up: sequence lamp reversed with voltage correct — close or swap, and what happens if you close now?
Full theory: Instruments & Safety Systems -
8 Maintenance of transformer
Also asked: “transformer maintaince and safety”, “Maintance in transformer”
Answer
Transformer rounds check oil, breathers, protection and earth: levels, silica, Buchholz, megger and connections.
- Oil level, colour and breakdown voltage with silica breather blue-dry, not pink-wet.
- Buchholz relay free of gas with protection and temperature trips proved.
- Windings meggered phase-to-phase and to earth with values logged hot and cold.
- Keep breathers, radiators and marshalling boxes clean, dry and vermin-proof with neutrals earthed per diagram.
Surveyor follow-up: silica pink with oil level normal — dry out, renew or run, and what first?
Full theory: Transformers, Diodes & Thyristors -
9 What is Ip56 means
Also asked: “What is IP56”, “• what does ip56 means (what is ingress number”
Answer
IP56 means dust-tight enough and jet-proof: first digit solids, second water — heavy seas break nothing.
- Letters IP with two numerals plus an optional impact digit on polycarbonate gear.
- First digit 5 blocks harmful dust; second digit 6 survives powerful water jets and heavy seas.
- IPX5 instead guards water only; IP2X instead guards fingers and shock only.
- Match the rating to the space — deck gear IP56, engine flats lower, hazardous spaces flameproof as well.
Surveyor follow-up: IP56 light offered for the funnel deck — accept it, and what do the 5 and 6 each promise?
Full theory: Instruments & Safety Systems -
10 Difference between auto transformer and soft starter
Also asked: “Soft starter & auto tranformer stater difference”
Answer
Autotransformers tap voltage in iron, soft starters chop it in silicon: taps are big and cheap per start, silicon is smooth and dear.
- Autotransformer gives fixed reduced-voltage steps with high torque per amp but bulky iron and limited duty.
- Soft starter ramps continuously with thyristors for gentle torque climb and current cap at a price.
- Torque follows voltage squared on both — curves must clear load torque at every speed or raise the tap.
- Pick taps for big thrusters started rarely, silicon for pumps and fans started kindly and often.
Surveyor follow-up: thruster stalls at the end of ramp — tap up, limit up or load down, and what proves it?
Full theory: Transformers, Diodes & Thyristors -
11 Got electrical and motor
Also asked: “Got- motor and electrical”
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12 Result- Electrical Passed
Also asked: “Results- electrical mep pass”, “Result- Electrical Pass”
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13 Dead man handle
Answer
Dead-man controls die with the hand: release the grip and springs break the circuit to stop the machine.
- Spring-return grip must be held for the contactor coil to stay energised and the motor to run.
- Releasing or collapsing grip opens control supply, drops the contactor and stops the drive dead.
- Fitted where an unattended machine kills — winches, cranes, lifts and test rigs with one operator.
- Prove by release test at no load: time the stop, then prove restart needs a fresh deliberate grip.
Surveyor follow-up: handle tied open with rope for a long lift — convenient or detainable, and what breaks first?
Full theory: Motor Starters — Taming 8–10× Current -
14 What is PID controller?
Also asked: “What is PID controller? How is proportional”
Answer
PID holds the setpoint against disturbances: proportional pushes now, integral kills offset, derivative brakes overshoot.
- Proportional answers the present error fast but leaves steady offset under load.
- Integral sums past error to wipe offset where steering and engine control demand zero droop.
- Derivative reads the error slope to damp swings where lags shift with load.
- Marine three-mode PID suits quick large disturbances — tune gains to load, never copy another ship’s numbers.
Surveyor follow-up: steering hunts with offset gone but overshoot wild — raise P, I or D, and what proves it?
Full theory: Marine Pneumatic & Electronic Process PID Controllers -
15 I (a) Discuss on Wheatstone bridge and one of «'s applications, namely “on all electric steering
Answer
Wheatstone finds unknowns by balance: four arms, null galvanometer, ratio known — steering repeaters copy the unbalance into helm.
- Balance the bridge until the galvanometer reads null; unknown resistance falls out of the known ratio arms.
- Bridge excitation must stay steady — drifting supply reads as drifting measurement on every repeater.
- All-electric steering uses bridge unbalance as the helm signal: bridge lever moves one arm, the torque motor hunts its mate back to null.
- The same balance trick measures temperature, strain and cable faults wherever resistance carries the signal.
Surveyor follow-up: repeater hunting with the bridge proved balanced and supply steady — transmitter, receiver or hunting gear first?
Full theory: Steering Gear Control Systems — Telemotor, Hunting Gear and Floating Lever -
16 Safety pass electrical repeat
Also asked: “Elec pass mep repeat”
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17 With reference to electric arc welding: butt weld (6) (a) Drawa labeled sectional sketch of a satisfactory
Answer
Draw a full-penetration butt: bevelled edges, honest root gap, backing where needed, crown and root proved sound.
- Butt beats lap for strength — bevel edges past 5–6 mm with multi-pass metal filling the vee.
- Single-side welds need backing bar or tape with at least 6 mm root opening and included angle trimmed to plate thickness.
- Thick plates earn narrow-gap vees with wider roots — 20° with 12 mm root on 50 mm plate saves a fifth of the metal.
- Prove by back-gouged root, even ripples, no undercut or slag lines — then stamp the welder, not just the joint.
Surveyor follow-up: butt welded one side with no backing and a tight root — penetration, strength or survey first to fail?
Full theory: Shipbuilding Materials, Welding and Weld Defects -
18 (answer needs to be confirmed before studying
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19 Sketch a reverse current trip
Answer
Draw the reverse-power relay with voltage and current coils on a laminated core driving an aluminium-disc trip with delay.
- Voltage coil watches bus volts while the current coil watches generator amps on the same core.
- Healthy export torques the disc one way; motoring reverses power and drags the disc to the trip contact.
- Time delay rides through synchronising swings and motor-starting dips so only sustained motoring trips.
- Trips the breaker before a dead prime mover motoring damages engines that shut down on lost oil pressure.
Surveyor follow-up: relay trips on paralleling with both sets healthy — settings, delay or phasing first to blame?
Full theory: Switchboards & Protection — MSB to Emergency Bus -
20 Why to increase power factor
Answer
High power factor means thin current for the same kilowatts: less heat, less drop, more generator for real work.
- Low factor from lightly loaded motors and transformers magnetises iron with idle current that heats cables.
- Harmonic currents distort the sine further, stealing capacity while doing no shaft work.
- Correction by loading, capacitors and clean waveforms frees generator amps for propulsion and cargo gear.
- Prove by ammeter falling at steady kilowatts after correction — the surveyor reads current, not cosines.
Surveyor follow-up: power factor low with the ship lightly loaded at night — load up, correct or accept, and what overheats first?
Full theory: The Alternator and Switchboard — AVR, Load Shedding and the Automatic Plant -
21 Asking many things from electrical
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22 Mep electrical repeat
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23 Some questions on electricals also that I didn't remember
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24 What is Static electricity. Examples
Also asked: “What is static electricity?”
Answer
Static is charge separated by friction and held on an insulator: on a tanker it is generated in the flowing fuel itself.
- Friction during relative motion separates positive and negative charge, which stays on materials that cannot conduct it away.
- On tankers it arises when liquid flows turbulently through the loading line into the ship’s tank, and during cold operations.
- If two charged bodies come close enough the potential difference jumps as a spark, and a flammable vapour ignites.
- That is why loading is slowed, bonding and earthing are fitted, and hoses are not disconnected while flow continues.
Surveyor follow-up: a spark at the manifold during a fast load with the bonding strap broken — what else is still exposed?
Full theory: Safety on Deck — Stored Energy, Isolation and Hazardous Areas -
25 What is likely to be the reasons for the failure? (c) (4) Give details of what checks are made after the engine has been stopped, both regard to (i)Mechanical checks and; (i) Electrical checks
Answer
Most no-start failures are one of two things: carbon on the injector tips, or an engine stopped out of sequence instead of on the fuel lever.
- Carbon on the injector tips is the classic cause: the engine was firing, the fault went unnoticed, and when stopped the deposit hardened, so atomisation failed.
- The checks are to open and inspect every injector, clean and overhaul them, and check the fuel oil condition and change it if required.
- If the engine turns freely but will not fire on fuel, check it was stopped properly — the fuel control lever to the stop position, not by shutting a tank valve.
- Then the electrical side: the battery and charging state, the starting air, the fuel solenoid and the governing trip, each proved rather than assumed.
Surveyor follow-up: engine turns freely, no fuel, injectors clean — which half of the check finds the fault now?
Full theory: Diesel Engine Types — 2-Stroke Crosshead vs 4-Stroke Trunk -
26 Why transformer makes humming noise? How to overcome?
Also asked: “why transformer produces humming sound?”
Answer
A transformer hums because its core magnetostricts at twice supply frequency and the laminations ring: looseness turns hum into roar.
- Alternating flux makes the iron core change length each cycle — magnetostriction — so the laminations vibrate at twice the supply frequency.
- The laminations isolate the core so eddy currents do not add to the noise, but a loosely clamped core rattles instead of humming.
- Hysteresis and eddy losses add heat and noise; total core loss is the sum of the two, and both are constant losses.
- Tighten the core clamps and the yoke bolts, check for loose laminations or a cracked core, and mount the transformer on anti-vibration pads.
Surveyor follow-up: transformer roaring on load with a recently re-cored transformer — is the clamp, the laminations or the mount?
Full theory: Transformers, Diodes & Thyristors -
27 With reference to an emergency source of electrical power in cargo ships:- (a) Describe a typical power source. (6) b) Give a typical list of essential services, which must be supplied simultaneously. (5) tested. (C) Exp
Also asked: “With reference to an emergency source of electrical power in cargo ships:- (a) Describe a typical power source. (6) b) Give a typical list of essential services, which must be supplied simultaneously. (5) tested. (C) Explain how the emergency installation can be periodically”, “1, With refere we to an emergency source of electrical power in cargo ships: (i) Describes atypical power sourge, . (6) (b”
Answer
The emergency source is the generator or the battery: the generator auto-starts, the battery bridges the gap and carries the load.
- A cargo ship uses an accumulator or a generator for emergency power; the battery connects automatically on loss of the main supply.
- Where the generator is not started and connected within 15 seconds, the battery is required as a transitional source for at least 30 minutes.
- The essential services supplied together are emergency lighting, steering gear, navigation, communications and the alarm systems.
- Test it periodically on load with the main board off, and prove the 45-second start and the full emergency board coming alive.
Surveyor follow-up: emergency generator started in 70 seconds with the batteries charged — what does the regulation require?
Full theory: The Emergency Generator — Location, Starting, Fuel and the Emergency Board -
28 Working on auto transformer
Answer
An autotransformer starter is a step-down transformer on the start side of the motor, tapped to limit the starting current.
- Three autotransformers in the start configuration give the motor a reduced voltage, and taps are set for the right current.
- Pressing start closes K1 and K2 together, applying reduced voltage to U1, V1 and W1 through the autotransformer.
- After a preset time delay, allowing the motor to run up, K1 opens and the autotransformer leaves the circuit.
- The motor then runs on full supply with part of the autotransformer winding merely acting as a series reactor, and the torque stays up through acceleration.
Surveyor follow-up: motor stalling at the end of the autotransformer start with the tap proved — raise the tap, extend the delay or unload the load?
Full theory: Motor Starters — Taming 8–10× Current -
29 Shore connection where located
Also asked: “Where is shore connection given”
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30 Working and types of rectifier
Also asked: “Types of rectifier and difference between them”
Answer
A rectifier turns AC into DC: half-wave, full-wave centre-tap or bridge by diode count, and controlled versions with thyristors.
- Half-wave uses one diode and gives the lowest ripple factor of nothing useful, so it is rarely used on ships.
- A centre-tapped transformer with two diodes gives full-wave rectification, and four diodes in a bridge give the same full-wave output.
- An equivalent three-phase bridge needs six diodes for full-wave operation.
- A diode has only two terminals and cannot control the output; a thyristor can, by delayed switching and the delay angle.
Surveyor follow-up: exciter rectifier built with six diodes and a variable output — is that a bridge or a controlled set, and what controls it?
Full theory: Transformers, Diodes & Thyristors
Source: 123 written papers and surveyor oral banks, 24,613 entries, merged into 17,210 topics. Ticks are stored on this device only.