Generally the above comments are correct. The most common system on ships is IT (normally 440V 3 phase 3-wire 60Hz) but sometimes on smaller ships there will be a 380V 3 phase 4-wire (60Hz or 50Hz - I have seen both) system as this means that phase-neutral is 220V and therefore there is no need for a transformer.

The principle is that an earth fault on a circuit will be detected through mandated earth fault detection but leave the circuit operational rather than tripping a vital service (as has been said above). As added security certain circuits such as steering (which has duplicated systems) will have both running while in critical locations.

There are also requirements for certain ships such as tankers which prohibit a 3 phase 4 wire system (at least in the cargo area) to prevent an earth fault current returning through the metal structure of the cargo tanks (but don't get me started on the justification for that one....)

Alasdair

Generally the above comments are correct. The most common system on ships is IT (normally 440V 3 phase 3-wire 60Hz) but sometimes on smaller ships there will be a 380V 3 phase 4-wire (60Hz or 50Hz - I have seen both) system as this means that phase-neutral is 220V and therefore there is no need for a transformer.

The principle is that an earth fault on a circuit will be detected through mandated earth fault detection but leave the circuit operational rather than tripping a vital service (as has been said above). As added security certain circuits such as steering (which has duplicated systems) will have both running while in critical locations.

There are also requirements for certain ships such as tankers which prohibit a 3 phase 4 wire system (at least in the cargo area) to prevent an earth fault current returning through the metal structure of the cargo tanks (but don't get me started on the justification for that one....)

Alasdair