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Re: AC polarity



Another anecdote about the importance of correct polarity--

When we installed computer terminals in our rather old science building
a few years ago, we found that the terminal in the secretary's office
kept burning out. We called in an electrician, who plugged a tester
into the outlet, said "The polarity's wrong, hot and neutral are reversed",
re-wired it and went on his way. Another terminal burned out.

Desperate, we called DEC, who sent a service person down. He asked if
there was a ground in the room, but there wasn't (lucky, it turned out,
for the secretary). We ran a wire to a radiator in another room to ground
his voltmeter, and on probing, he found that the third wire was hot, 117
volts to ground. It had been connected to the conduit, and a mis-wired hot
wire was touching the same conduit.

The upshot is that a live ground wire will read, to the plug-in LED testers,
just as if the hot and neutral are reversed. (That is the hot will be at
the same "polarity" as the "ground").
Stanley J. McCaslin Inet: mccaslin@pscosf.peru.edu
Assistant Professor, Computer Science Phone:402/872-2208
Peru State College, Peru, NE 68421 Home: 402/872-7595