I have been looking for the history of switching the neutral at each breaker. Although in most cases, it is not required per IEEE 45, USCG Title 45, and ABS just to name a few, I come across this in older steel vessels. I think it is a relic from the ol' ungrounded days. This would explain I see this in older ships that have been since retrofitted with grounded systems but kept the origional distribution system due to the expense. Can anyone shed actual knowledge on the history?
Naval ships don't use neutrals, but use 110/63V floating delta, where both terminals in receptacles are hot. The only time the neutral terminals are actually grounded is when fed via isolation transformers or isolated UPS, but that's restricted to very particular applications and done at the equipment, not the panel. This method of distribution lowers the voltage potential (which is important when considering damage control while flooded with saltwater) and increases fault tolerance- you can short out a phase to ground and the system will still work. There are, of course, no ground wires, just bonding to the ship's hull.
So, what you see are 3-phase panels with all "1-phase" circuits fed from 2-pole breakers and ungrounded cables.
I am not talking about navel ships but other steel marine vessels. Their AC systems are required to be grounded. Most of the older steel vessels I have encountered are breaking the nuetral at the breaker. All applicable standards state that this is optional, not a requirement. I understand in general why the Navy does what it does but it is not applicable to civilian application