220V 2-Wire Fully Floating No Neutral

[lranso1]

I work for a marine crane manufacturer and we have a customer that has a 220V 2-Wire Fully Floating No Neutral power supply on his ship. Does anyone have any experience with this type of supply? I am concerned that there will be a possible safety issue and can't find anything in my NEC book. Would anyone suggest I use a transformer to supply my components with a "normal power supply"? HELP!!!!!

 

[alehman]

I can't imagine this would be permitted. Sorry all I know about marine power it that the NEC doesn't apply, except for shore connections.

 

[waross]

If the ship is using an ungrounded system, don't use a grounded system. You may be responsible for serious and rapid hull corrosion. This has been discussed and explained on the forum several times. Equipment may be grounded for safety but the system must not be grounded and any ground faults on equipment must be repaired or the faulted equipment disconnected before connecting shore power.
respectfully

 

[BlownUp]

Every naval system I have come across is fully floating like this (MIL-STD-1399 requires it) and I think it is very common in marine applications. I think waross is on the right track about preventing galvanic corrosion but also maintaining system operation in the event of insulation failure. In a ship system loss of power can be a very serious issue. With a fully floating system a failure of one leg to ground does not necessarily cause the power system to shut down. Proper ground fault detection will indicate the problem and allow critical systems to be switched to other sources so the fault can be isolated and repaired.

 

[resqcapt19]

The NEC would permit this to be an ungrounded system. See 250.20(B).
Don