Insulated Neutral on Ships
The difference between land based power delivery and the earthing system on ships (most, but not all).
- Land based = Connected neutral & earth
- Earthing systems on ships = Insulated neutral, not connected to ships hull
Land based connections
- Main priority is maximum protection of people and livestock.
- Neutral & earth connected together at local substation (step down transformer), and also where the cable enters the building.
Earthing systems on ships
Most ships have an ‘insulated neutral’ electrical system.
As the name suggests, the neutral wire is insulated from the ships hull, which is the closest thing to a land based earth aboard ship, at sea.
Insulated Neutral Practical Differences
On land, an earth fault would cause the Residual Current Device, or RCD, to trip.
The system is designed for maximum protection of people & livestock.
At sea the main priority is safety of the ship.
If critical systems such as steering gear were the trip, due to a single fault, then it could potentially be catastrophic.
Therefore on ships a single earth leakage fault between the power and the ships hull, can happen without tripping the circuit.
What happens instead is that an alarm will be triggered on the ships earth fault monitor panel.
It is important that a single earth fault in an insulated neutral system is repaired as soon as possible.
This is because if a second fault should occur, then the circuit will trip, which could out the ship at risk.