Draw a circuit diagram from bus bar to any pump with all trips safeties

Draw it as the power flows: busbar, breaker, overload and trip, contactor, motor — with the safeties labelled on the way. From the busbar through a circuit breaker with a thermal-magnetic overload trip and, where fitted, a short-circuit trip. Then the contactor and its overload relay, which protects the motor on sustained overload and isolates it on a trip. Add the control side: the stop, the start push, the permissive and the remote or automatic start, with the trip relay wired to the coil. Label the pressures, temperatures and levels on the drawing — a diagram with no safeties named is half a diagram. Surveyor follow-up: pump drawing full current with the overload set at twice running current — is the setting or the load wrong?

The various loads on emergency bus bar

The emergency busbar carries only what must survive a blackout: steering, navigation, communications, emergency lighting and the alarms. Two steering gear circuits feed the emergency board, the other running from the main board. Navigation lights, navigation aids, radio and the emergency lighting circuits are on the emergency supply. The emergency generator and the battery set feed it, so it stays live when the main board is lost. Only a 440/220 V arrangement of those essential circuits is transferred — the galley and the cargo gear are not on it. Surveyor follow-up: galley circuits found on the emergency board at PSC — which loads should be there instead?

A busbar is the heavy copper spine of the switchboard: every generator and feeder connects to it, and it carries the current. Short copper bars from each generator’s circuit breaker connect to bars running the length of the switchboard. They are insulated, hard-drawn, high-conductivity electrolytic copper on permall-type insulators inside the cubicle. They are rigidly mounted to hold clearances under short-circuit conditions, and the joints are bolted with tinned surfaces. Cables come in on lugs and bolts at the bars, so the bar is the only place the whole ship’s power actually meets. Surveyor follow-up: bolted busbar joint found warm on a routine inspection — is it torque, cleanliness or the joint material?

Switchboard & Distribution — Most Asked Questions

5 questions asked about switchboard & distribution across the General paper, heaviest first.

Learn the system first

The Alternator and Switchboard — AVR, Load Shedding and the Automatic Plant Marine Batteries: Lead-Acid vs NiCd, Charging & 440/220 V Distribution Switchboards & Protection — MSB to Emergency Bus

5 questions 0 ticked

1 Draw a circuit diagram from bus bar to any pump with all trips safeties

Revise Sketch / drawing asked 4 times · across 1 examiner bank General
Answer

Draw it as the power flows: busbar, breaker, overload and trip, contactor, motor — with the safeties labelled on the way.
- From the busbar through a circuit breaker with a thermal-magnetic overload trip and, where fitted, a short-circuit trip.
- Then the contactor and its overload relay, which protects the motor on sustained overload and isolates it on a trip.
- Add the control side: the stop, the start push, the permissive and the remote or automatic start, with the trip relay wired to the coil.
- Label the pressures, temperatures and levels on the drawing — a diagram with no safeties named is half a diagram.
Surveyor follow-up: pump drawing full current with the overload set at twice running current — is the setting or the load wrong?
Full theory: Switchboards & Protection — MSB to Emergency Bus
2 Load connected on esb

Revise Theory asked 2 times · across 2 examiner banks General
3 The different loads on esb

Revise Theory asked 2 times · across 2 examiner banks General
4 The various loads on emergency bus bar

Revise Theory asked 2 times · across 2 examiner banks General
Answer

The emergency busbar carries only what must survive a blackout: steering, navigation, communications, emergency lighting and the alarms.
- Two steering gear circuits feed the emergency board, the other running from the main board.
- Navigation lights, navigation aids, radio and the emergency lighting circuits are on the emergency supply.
- The emergency generator and the battery set feed it, so it stays live when the main board is lost.
- Only a 440/220 V arrangement of those essential circuits is transferred — the galley and the cargo gear are not on it.
Surveyor follow-up: galley circuits found on the emergency board at PSC — which loads should be there instead?
Full theory: The Alternator and Switchboard — AVR, Load Shedding and the Automatic Plant
5 What is busbar

Revise Theory asked 2 times · across 2 examiner banks · 2 wordings merged General

Also asked: “What is bus bar?”
Answer

A busbar is the heavy copper spine of the switchboard: every generator and feeder connects to it, and it carries the current.
- Short copper bars from each generator’s circuit breaker connect to bars running the length of the switchboard.
- They are insulated, hard-drawn, high-conductivity electrolytic copper on permall-type insulators inside the cubicle.
- They are rigidly mounted to hold clearances under short-circuit conditions, and the joints are bolted with tinned surfaces.
- Cables come in on lugs and bolts at the bars, so the bar is the only place the whole ship’s power actually meets.
Surveyor follow-up: bolted busbar joint found warm on a routine inspection — is it torque, cleanliness or the joint material?
Full theory: Switchboards & Protection — MSB to Emergency Bus

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