The main switchboard is an intermediate installation in the ship’s power distribution circuit connecting the power generators and consumers.
The power generators on ships are auxiliary engines with alternators and the consumers are different engine room machinery 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 systems connected to the same.
If such isolation is not provided, even a short circuit in a small system can cause a blackout of the whole ship.
Therefore, different safety devices are used on board ships and installed on the main switchboard (MSB) and electrical distribution panels. This ensures the safe and efficient running of machinery and the safety of the personnel from electric shock even when one system is at fault.
The Important safety devices fitted on the main switchboard are:
- Circuit breakers: A circuit breaker is an auto-shut-down device that 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 come 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 currents. 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 switchboard individual panels wherein you cannot open the panel until the power of that panel is switched off.
Apart from this, maintenance and operational safety play an important part in the safety of the main switchboard.