Main Switchboard (LV)
The low-voltage main switchboard combines every generator's output onto a common busbar and splits it out through protected feeders, and its section splitting decides whether one fault blacks out the whole ship or just part of it.
Read more — Main Switchboard (LV) explained ▾
What Sets the Low-Voltage Main Switchboard Apart
The main switchboard is the single point where every generator on board feeds into a common busbar system before power is split out to distribution boards and final circuits. At low voltage, typically 380 to 690V on merchant vessels, it differs from a high-voltage switchboard, used on large cruise ships and some LNG carriers running at 6.6 or 11kV, mainly in insulation clearances and arc-flash energy involved, but the core job is the same: combine generator output safely, protect it, and share load between running generators without a fault in one section taking down the whole ship.
Main Components
Busbar system
Copper bars running the length of the switchboard, usually split into sections by bus-tie breakers so a fault or fire in one section can be isolated without blacking out the other.
Generator circuit breakers
Air circuit breakers rated to the generator's full load current, fitted with protection relays for overcurrent, short circuit, reverse power and, where applicable, differential protection.
Feeder breakers to distribution boards
Breakers sized to each downstream distribution board's load, coordinated with the generator breakers so a fault on a feeder trips only that feeder, not the generator supplying it.
Synchronising and load-sharing panel
Instruments and controls for bringing an additional generator onto the busbar in phase, matching voltage, frequency and phase sequence, and then sharing kW and kVAr load between running generators automatically or manually.
Protection relays and metering
Digital or electromechanical relays monitoring current, voltage, frequency and power factor on each section, feeding trip signals to the breakers and readings to the bridge and engine control room.
Selection and Sizing
Sizing follows total installed generator capacity, expected simultaneous load including starting currents of large motors, short-circuit fault current the busbar and breakers must withstand, and the degree of section splitting needed to meet the vessel's blackout-recovery and redundancy requirements. Passenger vessels and dynamic positioning vessels typically need finer sectionalising than a straightforward cargo ship.
Regulations and Class
Class rules, each society publishing its own electrical installation rules broadly aligned across IACS members, set minimum short-circuit withstand ratings, protection coordination requirements, and rules on section splitting for redundancy on vessels with class notations for dynamic positioning or enhanced survivability. SOLAS Ch. II-1 sets requirements for electrical installations generally, including emergency power arrangements that the main switchboard must be able to hand over to. Surveys check breaker settings against the approved protection coordination study and test insulation resistance at intervals set by class.
Typical Faults
- Protection relay settings drifted from the approved coordination study can let a downstream fault trip the generator breaker instead of the intended feeder breaker, causing a full blackout for what should have been a local trip.
- Loose busbar joints build up resistance and heat over time, occasionally to the point of an arc flash event.
- A synchronising equipment fault makes bringing a second generator online manually risky and slow exactly when the crew needs it fastest, during blackout recovery.
- Insulation degradation from moisture or salt ingress in engine room atmosphere shows up first as intermittent earth fault alarms before a hard failure.
What to Look for in a Supplier
- A protection coordination study delivered with the switchboard, not left for the yard or owner to commission separately.
- Short-circuit withstand rating with margin above the calculated fault current, not the bare minimum.
- Access and layout that lets breakers be withdrawn and tested without shutting down the whole board.
Keep the protection coordination study on board and check breaker settings against it after any relay replacement: a relay swapped in with default settings instead of the ship's coordinated settings is a common cause of a nuisance-trip blackout.
4 manufacturers · 4 models
ABB
1- ACB trip mechanism failure
- Busbar connection loosening from vibration
- Insulation breakdown
- Metering CT failure
- Compact, modular design saves valuable engine‑room space
- Integrated ACBs and metering reduce wiring complexity and improve reliability
- ABB’s proven service network simplifies maintenance and spare‑part logistics
- Built‑in monitoring (IR‑ready, torque‑checked busbars) supports condition‑based maintenance
- Higher upfront cost compared with generic OEM switchboards
- Requires ABB‑specific spares and trained personnel for optimal upkeep
- Limited to low‑voltage applications; not suitable for >690 V distribution
- Complex initial configuration may extend installation time on retrofits
Hyundai Electric
1- PMS communication error
- Generator breaker sync failure
- Busbar overheating
- Seamless integration with HiMSEN engine control reduces wiring complexity and improves monitoring
- Compact, modular layout simplifies installation on new‑build Korean vessels
- Standardised across Hyundai‑built fleets, facilitating spare‑parts logistics and crew familiarity
- Built‑in busbar temperature monitoring helps prevent overheating incidents
- Reported PMS communication errors can affect system diagnostics
- Generator breaker synchronization failures have been observed in the field
- Busbar overheating issues require regular inspection and may increase maintenance workload
- Limited aftermarket support outside of Korean shipyards and Hyundai service network
Schneider Electric
1- MCCB trip coil failure
- Busbar support insulator cracking
- Earth fault relay nuisance tripping
- Form 4 separation meets stringent marine safety standards
- Integrated MCCB and earth‑fault relay simplify protection scheme
- Schneider Electric brand reputation for reliability and support
- Modular layout allows easy expansion or reconfiguration on board
- Reported MCCB trip‑coil failures can lead to unexpected loss of supply
- Busbar support insulators have been known to crack under vibration
- Earth‑fault relay may nuisance‑trip in high‑harmonic environments
- Annual cleaning and inspection are mandatory, increasing maintenance workload
Siemens
1- Withdrawable unit interlock failure
- Busbar insulation aging
- Relay malfunction
- Ventilation fan failure
- Withdrawable unit design allows hot‑work and maintenance with minimal interruption to the power network.
- Integrated protection relays reduce external wiring and simplify fault management.
- Compact, modular construction fits confined engine‑room spaces typical on modern vessels.
- Robust busbar system handles high fault currents and provides reliable current carrying capacity.
- Marine‑approved certifications (IMO D-2, DNV GL) ensure compliance with shipboard safety standards.
- Higher upfront cost compared with conventional fixed LV switchboards.
- Requires regular thermographic surveys and ventilation fan checks to avoid overheating failures.
- Busbar insulation can age over long service periods, necessitating periodic inspection or replacement.
- Complexity of the withdrawable system may demand specialised Siemens training for troubleshooting.
- Voltage range limited to 380‑690 V, unsuitable for vessels requiring higher LV levels.