What are the Main Safety Devices for Main Switch Board on Ship?

The Main switch board is an intermediate installation in the ship’s power distribution circuit connecting the power generators and power consumers. The power generators on ships are auxiliary engines with alternators and the consumers are different engine room machineries such as motors, blowers etc.

It is very important to isolate any type of fault in an electrical system supplied from the main switchboard (MSB) or else it will affect all the other system connected to the same. If such isolation is not provided then even a short circuit in a small system can cause blackout of the whole ship.

Therefore, different safety devices are used on board ship and installed on the main switchboard (MSB) and electrical distribution panels. This ensures safe and efficient running of machineries and safety of the personal from electric shock even when one system is at fault.

engine control room

The Important safety devices fitted on main switch board are:

  • Circuit breakers: A circuit breaker is an auto shut down device which activates during an abnormality in the electrical circuit. Especially during overloading or short circuit, the circuit breaker opens the supplied circuit from MSB and thus protects the same. Different circuit breakers are strategically installed at various locations.
  • Fuses: Fuses are mainly used for short circuit protection and comes in various ratings. If the current passing through the circuit exceeds the safe value, the fuse material melts and isolates the MSB from the default system. Normally fuses are used with 1.5 times of full load current.


  • Over current relay: OCR is used mainly on the local panel and MSB for protection from high current. They are installed where a low power signal is a controller. Normally relays are set equivalent to full load current with time delay.
  • Dead front panel: It is another safety device provided on the Main switch board individual panels wherein you cannot open the panel until the power of that panel is switched off.

Apart from this, maintenance and operational safety plays an important part for the safety of main switch board.

You may also like to read-Single Phasing in Electrical Motors: Causes, Effects, and Protection Methods

References: Book on Marine electro technology by D.T HALL


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  2. I need to know that if any short circuit or overload is occured while shore supply breaker in close position that time the breaker will trips or continue it’s action?

  3. Hi, good day.
    Onboard What are the safety equipments in electrical hazardous are???. And what are their characteristic??

    Thanks in advance

  4. I load on the shore power at 5pm and everything went on smoothly since we had an automatic system onboard where it’s synchronised and changeover automatically. At about 0350hrs the next morning a heavy down pour …lightning and thunder for about an hr or so which causes blackout and ships generator just automatically cuts in and took over the load, then later in the I tried switch back to shore power it fails to connect due to a fault alarm kept coming on the control panel.They synchronised well but fails to load cos of this alarm …ALARM PROTECTION SHORE LINE.I’ve tried all the ideas and techniques still it giving out this alarm,anyone have any idea plis send me an email..thanks.

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