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Re: Electrics + Genius = Not !

To: Nickbk@aol.com
Subject: Re: Electrics + Genius = Not !
From: "W. R. Gibbons" <gibbons@northpole.med.uvm.edu>
Date: Tue, 25 Jun 1996 11:23:18 -0400 (EDT)
On Mon, 24 Jun 1996 Nickbk@aol.com wrote:

> Fellow Shop Rats-
> 
> Thanks for all the quick responses...
> I got responses which discussed sine way theory, and how it gets to be 220v,
> and believe it or not, it made perfect sense and I think I even understood it
> !
> Unfortunately, most everyone who responded seemed to think that I ought to
> have a red wire somewhere in the bunch, making four connections in total.
> List wisdom also seemed to think that the neutral wire was a kind of extra
> (safety ground), but that the green wire should be attached to the ground,
> with the black and red carrying the heavy stuff. Now I am most confused...The
> compressor has only 3 connections (including the grounded green wire) and the
> outlet on the wall only has 3 prongs. So, where do I hook up this illusive
> forth wire if I had it ? I know that I have some sort of 220v coming out of
> the wall, and the compressor says that it is 220v all over it. Am I missing
> something here ?

I hired a genuine licensed electrician to do a bunch of wiring in my 
house, including a 220V outlet in the garage.  He put in 4 wire cable 
(black, white, red, green) from the breaker box to the receptacle.

20 years later, I hired another licensed guy, highly recommended, to wire 
a 220 volt outlet for my table saw.  I saw him running the circuit with 
ordinary two conductor plus ground, and questioned it.  He said either 
way works.  You don't actually need the white neutral.

I have since wired up a 220 volt dust control system, and sure enough, 
you are right, both the motor and the plug have only three connections.  
So reason it out.  The only way to get 220 is with two wires, each of 
which has 110 v 180 degrees out of phase with each other, so the 
difference between the two is 220 v at peak.  You don't have to worry 
about the neutral, you don't need it.  You do need a ground.

So I assume your newly purchased rubber wire for the cord to your
compressor has 3 conductors--white, black, and green.  It is meant for
110, but no matter.  Connect the green to the ground of your compressor
and to the ground lug on your plug.  Make very damn sure you KNOW which is
the ground lug by checking the socket it is going in to. 

Use the white to link one hot side of your plug and the (-) terminal of 
your compressor.  Use the black to link the other hot side of your 
plug and the (+) side of your compressor.  Bob's your uncle.

Anyone disagree?  Do this of course, at your own risk.  I am not an 
electrician, nor do I play one on tv.

   Ray Gibbons  Dept. of Molecular Physiology & Biophysics
                Univ. of Vermont College of Medicine, Burlington, VT
                gibbons@northpole.med.uvm.edu  (802) 656-8910


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