Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!elroy.jpl.nasa.gov!swrinde!ucsd!nosc!crash!simpact!jeh From: jeh@dcs.simpact.com Newsgroups: sci.electronics Subject: Re: What's acceptable voltage ground-neutral? (it depends.) Message-ID: <1991Apr16.153011.2278@dcs.simpact.com> Date: 16 Apr 91 22:30:11 GMT References: <1991Apr13.131621.225@mandata@uunet.uu.net> Distribution: na Organization: Simpact Associates, San Diego CA Lines: 32 In article <1991Apr13.131621.225@mandata@uunet.uu.net>, jscott@mandata@uunet.uu.net (Jeff Scott) writes: > I measured the voltage between the neutral and ground on the outlets > around my home. Some read .25 VAC and some read .67 VAC (one or the other, > nothing inbetween). Any opinions on whether this is OK? What you are measuring is actually the voltage drop in the neutral wire between wherever you're measuring and the tiepoint at the main box where the two are bonded together. Current flows in the neutral wire, hence there's a voltage drop. No current (is supposed to) flow in the ground wire, hence no drop... which is to say that you'll get the same reading with one probe of the DVM at the outlet neutral and the other probe at the ground/neutral tiepoint. The voltage drop will obviously vary with the amount of current running through the circuit. Say you're drawing 1 amp, if you just have 0.1 volt drop in the neutral wire, you are looking at only 0.1 ohm back to the service entrance. If 10 amps were flowing in the same circuit, you would measure a full volt of drop. This is quite a reasonable value. The standard wire tables will tell you that it would take many miles of 14 AWG copper to add up to a tenth of an ohm, but of course, nearly all of the R comes from the splices, not the wire itself. Paradoxically, if you ever measure ZERO voltage between neutral and ground anywhere but at the service entrance, with a heavy load on the circuit, this means trouble -- specifically, that some clown has connected neutral and ground together other than at the service entrance. Of course, a higher voltage drop means trouble too: A high-resistance path in the neutral line. --- Jamie Hanrahan (x1116), Simpact Associates, San Diego CA Internet: jeh@dcs.simpact.com, or if that fails, jeh@crash.cts.com Uucp: ...{crash,scubed,decwrl}!simpact!jeh