Main Switchboard (MSB)
The main switchboard is the single point where every generator's output is paralleled, protected and split across bus sections; how it is sectioned decides whether one fault causes a local trip or a full blackout.
What to check on a Main Switchboard (MSB).
6 models from Kongsberg Maritime in Main Switchboard (MSB). Below: the full model list.
What Defines a Main Switchboard
The main switchboard (MSB) is the busbar assembly that receives power directly from the ship's generators (diesel generators, shaft generator, emergency generator through a change-over, or shore connection) and distributes it onward to distribution boards, group starter panels and large consumers. It differs from a downstream distribution board in one essential way: everything on the MSB is rated for full generator fault current, while boards further down the chain only need to withstand the fault current available after upstream protection has cleared. The MSB is also where generators are synchronised and paralleled, and where the ship's electrical system is split into independent sections through a bus-tie breaker.
Legend
- generator breaker
- busbar section A
- busbar section B
- bus-tie breaker
- outgoing feeders
Main components
Busbar system
Copper busbars, air-insulated in most merchant ships or arc-resistant enclosed on passenger and offshore vessels, form the backbone. The bus is split into at least two sections joined by a bus-tie breaker so a fault on one section can be isolated without losing the other.
Generator and bus-tie breakers
Air circuit breakers (ACBs) connect each generator to its bus section and connect the sections together. They carry protection relays for overcurrent, short-circuit, reverse power and, on larger plants, differential protection.
Read the full guide
Synchronising equipment
A synchroscope or automatic synchroniser matches voltage, frequency and phase sequence before a generator breaker closes onto a live bus; getting this wrong causes a violent out-of-phase closure that can shear a generator coupling.
Metering and monitoring
Ammeters, voltmeters, frequency meters, power factor and kW meters per generator, plus an insulation monitoring device (IMD) that continuously watches for earth faults on the ship's typically ungrounded distribution system.
Selection and sizing
An MSB is specified around the connected generating capacity, not the average load:
- Rated busbar current, sized above the sum of generator full-load currents with margin for future load growth
- Short-circuit withstand rating in kA for one second, based on a fault current calculation for the whole plant
- System voltage: 400V/440V is common on smaller ships, 690V or 6.6kV high-voltage systems appear on large cruise ships, LNG carriers and diesel-electric offshore vessels
- Number of generator and bus-tie panels, and whether shore connection and shaft generator feeders are required
- Degree of protection suited to the engine room environment
Class and regulatory requirements
SOLAS Chapter II-1 requires that a single fault cannot leave the ship without essential electrical services, which is the reason class rules insist on at least two independent bus sections with a bus-tie breaker capable of isolating a faulted section. Classification societies apply their own rules for electrical installations, largely aligned with IACS Unified Requirements for electrical systems, covering short-circuit calculations, discrimination between protective devices, and segregation of cabling. Switchboards are surveyed at each class renewal: insulation resistance testing, protection relay function tests, and a visual check of busbar joints and cable terminations for overheating are standard survey items.
Typical faults
| Fault | Cause | Consequence |
|---|---|---|
| Arc flash / short circuit | Insulation degradation, dust or moisture bridging phases | Switchboard destroyed, blackout, risk of injury to nearby crew |
| Loose busbar joint | Thermal cycling loosening bolted connections over years of service | Local hot spot, eventual arcing and fire |
| Failed synchroniser | Worn contacts or drifted calibration | Generator closed out of phase, coupling or prime mover damage |
| Undetected earth fault | IMD faulty or alarm ignored | A second earth fault produces a phase-to-phase short circuit |
What to look for in a supplier
- Type-test certificates to IEC 61439-1/2 for the assembly, not just component-level approvals
- Class type approval covering the relevant flag and voltage class
- A documented short-circuit and arc-flash study for the specific configuration ordered
- Availability of spare breakers, relays and IMD units compatible with the installed base
- Local commissioning and service support in the yard's region
A yearly thermographic scan of busbar joints and cable lugs while the switchboard is under load catches loose connections weeks before they become a fire, and it costs a fraction of the downtime a burnt-out section would.
Models in this type.
The best-documented model of each manufacturer first, then the next — 6 of 6 models in Main Switchboard (MSB). Every row links to full specifications, documents and service notes.
Manufacturers.
All 29 manufacturers with models of Main Switchboard (MSB). Names with a manufacturer page open it; the others open a search across the full library.
All manufacturers- Seoul Electric Wire Co., Ltd.1
- Shanghai Complee Instrument Co. Ltd4
- Siemens147
- SOREEL SOCIETE DE REALISATION D'EQUIPEMENTS ELECTRIQUES SAS1
- Taiyo Electric Co., Ltd., Gunma Plants Controller Factory1
- Terasaki Electric81
- Wärtsilä SAM Electronics GmbH1
- Weigel Meßgeräte3
- Wuhan Xiangyi Zhongxin Technology Development Co., Ltd.1
Also in Power Distribution.
The other equipment types in this category.
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Is Main Switchboard (MSB) data free?
Yes. Every model page, every guide and every datasheet for this type is readable without an account. An account adds saved searches and requests, nothing is taken away.
My model is missing — what now?
Send us the nameplate. We identify it by hand, add it to the library, and if you need a part or a service, the request is already on our desk.
Can you source a Main Switchboard (MSB) part?
Yes. Tell us the manufacturer, the model and what you need — a person reads every request and replies by e-mail.