Question 1

Single phasing of motor?

Accepted 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?

Question 2

intrinsically safe equipment

Accepted 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?

Question 3

Speed control of Motor

Accepted 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?

Question 4

What is reverse power relay?

Accepted Answer

The reverse-power relay stops a dead generator motoring: direction-sensing trip that sheds the set before the board feeds it. Watches power direction, not just current — AC reverse current hides too small to catch directly. Generator output falling below the preset sheds the breaker before busbar power drives the stator. Protects the prime mover stalled by fault from being dragged as a motor load. Prove with overcurrent and preferential trips together on schedule, not alone. Surveyor follow-up: two sets parallel, one engine flames out — which breaker opens, and what does the relay see?

Question 5

What to check before shore connection?

Accepted 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?

Question 6

Fuses and fuse ratings

Accepted Answer

Fuses rate to the cable with discrimination upward: motor tables pair relay range to diazed HRC backup. Size to full-load current per the motor table — relay range below, HRC backup above for short-circuit duty. HRC cartridge to 80 kA breaking beats rewireable wire, which crews abuse with wrong gauges. Small overloads belong to relays, not fuses — an HRC passes 20% over for hours before blowing. Prove discrimination upward so the branch fuse dies before the board breaker trips the ship. Surveyor follow-up: branch fuse blows with the motor healthy — rating, discrimination or downstream fault?

Question 7

What is Ip56 means

Accepted 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?

Question 8

Earth fault detection

Accepted Answer

Earth faults show on lamps then meters then breakers: dim lamp names the leg, resistance meter proves high impedance, elimination finds the circuit. Healthy lamps glow equal half-bright; the faulted leg dims or dies while sisters brighten. Lamps miss high-impedance faults — resistance meters with small DC injection prove those. Find by opening breakers section by section to essential-safe order until the fault clears. An earth on an earthed system equals a short — clear fast with automatic protection, not patience. Surveyor follow-up: lamps equal with the insulation alarm sounding — high impedance or healthy, and what next?

Question 9

Collision bulk head

Accepted Answer

The collision bulkhead seals the bow: not too far forward to crush at once, not too far aft to flood deep. Foremost bulkhead bounding the forepeak against bow damage. Positioned by rule between minimum and maximum distances from the forward perpendicular by length. No doors, manholes or ducts pierce it except tightly controlled piped penetrations. One flooded bow compartment survivable — progressive flooding aft never allowed. Surveyor follow-up: pipe through the collision bulkhead with valves both sides — allowed or not?

Question 10

what is insulation resistance

Accepted Answer

Insulation resistance is the leakage defence in ohms: radial resistance to stray current, falling with length, heat and damp. Healthy current runs along the core; leakage creeps radially through insulation to earth. Longer cables leak more — resistance falls as length and wet heat rise. Low-voltage gear expects megaohms, high-voltage tens of megaohms and up. Megger dead, trend the readings — a falling curve condemns before the fault flashes. Surveyor follow-up: readings halved since last month with load steady — heat, damp or damage, and what next?

Electrical (Function 5) — Most Asked Questions

Protection & Circuit Breakers

Electrical General

Batteries & Emergency Power

Motors & Starters

Auxiliary Engine / Generator

Cables, Insulation & Earthing

Generators & Power Management

Deck Machinery (Electrical)