- In the event of a single earth fault, no earth fault current flows through the ship's hull due to the insulated neutral, minimizing fire hazards.
- The hull does not carry current, ensuring safety from electrical currents passing through the structure.
- A single earth fault does not cause generator breaker tripping, avoiding sudden blackouts or operational disruptions.
- Harmonic currents caused by third harmonics in the generated voltage are prevented from flowing through the neutral, protecting the generator windings from overloading.
- Only one system voltage (line-to-line) is possible, unlike earthed neutral systems which also provide line-to-neutral voltages.
- While an earth fault alarm and phase indicator are triggered, locating the exact fault location requires a time-consuming trial-and-error process.
- In cases of inductive or capacitive faults to earth, surge voltage can rise 3.5 to 4 times the system voltage, risking insulation failure and system collapse.
A metallic resistor is inserted between the neutral point and the ship’s hull to limit earth fault current.
The resistor’s value is determined by:
$$R=\frac{V}{\sqrt3I}\:$$
Where,
- V = Line voltage,
- I = Full load current.
Metallic resistors are used for their stability, low maintenance, and ability to prevent arcing grounds.
The risk of electric shock is considered equally dangerous in both earthed and insulated neutral systems. In an insulated system, normal leakage currents from capacitance and surface leakage, along with the possibility of earth faults, mean that touching live parts still carries a considerable shock risk. Similarly, in an earthed system, line-to-neutral voltages (even those as low as 110 or 250 volts) can be lethal under certain shipboard conditions, making neither system inherently safer regarding electric shock than the other. Appropriate safety precautions are essential for both systems.