Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sdd.hp.com!wuarchive!uwm.edu!bionet!agate!dog.ee.lbl.gov!nosc!manta!norton From: norton@manta.NOSC.MIL (Scott Norton) Newsgroups: sci.electronics Subject: Re: What's acceptable voltage ground-neutral? Summary: Ships have ground and neutral isolated, can float 100s of volts. Keywords: Power, ground, neutral, MIL-STD-1399, shipboard power Message-ID: <1926@manta.NOSC.MIL> Date: 22 Apr 91 02:45:18 GMT References: <1991Apr13.131621.225@mandata@uunet.uu.net> Organization: Space & Naval Warfare Systems Command Lines: 17 To take this thread off on a tangent, I want to point out to anyone who is designing for US Navy shipboard applications, that on ships, neutral and ground are purposely isolated. The reason for this is to make the power system more survivable; a ground in any phase causes no disruption to service. But because of this arrangement, neutral and ground can float a couple of hundred volts apart. In a casualty that grounds one phase, neutral will move to 380 volts from ground in the 440 primary power distribution, or 103 volts for the 115 volt branches. As a result of designers failing to account for this possibility, at least one brand of surge supressor has been known to short out and catch fire when used on a ship. Apparently, the surge capacitors or MOVs were not spec-ed for the voltage float. LT Scott A. Norton, USN