At 11:23 6/25/96 -0400, W. R. Gibbons wrote:
>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
>
>
Ray:
Nick is connecting to a dryer plug (probably 40 amps) and that plug MUST
have a neutral. The reason is that control and auxilliary circuits often
use 110 volts, even on a 220 volt machine. For example; the dryer light
runs off 110 volts, the motor relay (if it has one) runs off 110 volts, etc.
Simply running two phases and a safety ground guarantees that the safety
ground carries current and this is a no no.
Any receptacle that has a neutral connector must have a neutral service wire
run to it.
Your advise to Nick will get his compressor to run. The use of wrongly
coded wire and neutral/ground interchanges is common and a safety hazard to
people who may have to work on the compressor at a later date. The
compressor calls for two phases and a safety ground - the plug has two
phases and a neutral. The National Electric Code exists to make sure such
connections are not accidentally made.
There are two solutions:
a. Buy some proper 3 conductor cable and run the black and red to
each side of the compressor. Run the black and red to each hot side of the
dryer plug. Do not connect the white or green/copper to either the plug or
the compressor. Run a separate and permanent safety ground from the
compressor motor frame to a ground point.
b. Do it right and have a three wire service run from the main
distribution panel to the garage. The garage panel (box) will have red,
black, and white wires as well as a copper safety ground. Then you can
connect up all sorts of 220 and 110 volt sockets safely.
Comment: Both your electricians probably did the job right. You should
find that the second electrician also installed a socket (20 - 30 amps) that
had only two hot connections and a safety ground. You meet code as long as
you don't go inside the box and try to install a three conductor socket.
Comment: You can get 220 volts from either phase to phase of a 220/110 volt
split phase service or phase to neutral of a 380 volt 3 phase Y service.
The former is residential service and the latter is used in light industry.
Jon N. LeChevet
One lawyer will starve to death in a small town.
Two lawyers in town
will wind up owning the town.
Anon.
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