The function of an electrical system is to safely convey the power from the source to the various consumer equipment connected to it. A ship's electrical system can be of two types:
> Neutral Insulated system
> Neutral Earthed system
Neutral Insulated system
An insulated system is one that is totally electrically insulated from earth (ship’s hull). In a neutral insulated system, the star point of the source is not connected to earth. Hence there happens to be only 3 leads (3 phase wires R,Y,B) emanating from the source.
Advantages of insulated neutral systems:
> Reduced risk of electric shock
> Reduced risk of fire and explosion
> Reduced risk of damage to equipment
Disadvantages of insulated neutral systems:
>More difficult to troubleshoot faults
> Requires more complex and expensive protection equipment
Neutral Earthed system
In a neutral earthed system, the star point is earthed to ground. So 4 wires emanating from source (3 phase and 1 neutral).
Disadvantages of earthed neutral systems:
> Increased risk of electric shock
> Increased risk of fire and explosion
> Increased risk of damage to equipment
Why is an earthed neutral system not used in tankers?
An earthed neutral system is not used in tankers because of the risk of explosion. If an earth fault current occurs in an earthed neutral system, it could circulate in the ship's hull within the hazardous zone. This could cause an explosion of the flammable cargo.