At 11:51 6/27/96 -0400, W. R. Gibbons wrote:
>On Wed, 26 Jun 1996, Jon N. LeChevet wrote:
>
>> 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.
>
>I never thought of that, Jon, obviously you know a hell of a lot more
>about it than I do (a little knowledge is a dangerous thing). But now, if
>others will bear with me, I'd like to indulge my curiosity. I am 99% sure
>my dryer has a three prong plug. So does my electric stove. Certainly,
>each has 110 v circuits for things like the lights, so the three prongs
>must be 110, 110, and neutral. Neither appliance has a separate ground.
>
>Apparently, then, modern 110 volt appliances are grounded automatically
>when you plug them in, but modern 220 volt appliances are not generally
>grounded unless you run a separate wire to a ground. Why not simply have
>a 4 prong plug? You'd think that very few homeowners are going to know
>how to attach a separate ground. In fact, my stove was installed by the
>appliance store, and they never ran a ground.
>
>Jon Comments:
Four prong plugs are available, but not in much demand since code allows for
three prong plugs. I agree with you that an integral ground for 220 volt
appliances makes sense. Until code changes, we will have three prong plugs.
I would also get on your appliance store and ask then why they left a safety
hazard in your house.
Jon continued:
>
>> 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.
>
>> 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.
>
>That obviously is a better way to wire it. I do think, though, that it
>would be going to extremes to discard the wire he has already bought. If
>he gets the proper wire, he is only going to use two of the conductors.
>That is going pretty far to avoid having a hot white wire inside the
>junction box. I'd hope that anybody who opens the junction box on the
>motor is going to be sensible enough to unplug the unit first. I would
>definitely do it as you say, but I would use the white and black
>conductors in the cable he has, wrap a few turns of black tape around the
>end of the white wire in the motor's junction box to indicate it is hot,
>and run the separate ground. Anybody who assumes the white wires in a
>junction box cannot be hot hasn't changed many light fixtures.
>
Jon Comments:
Using marker tape at both ends of a wire is an acceptable and recognized way
of changing color. Any tradesman skilled in electricity would recognize this.
>The stores are full of tools made to run on 110 or 220, like my Delta
>Contractor's saw and my dust collector. I would have to look, but I would
>wager my saw uses a line cord that is color coded for 110. The
>instructions for changing the saw to 220v operation don't advocate buying
>a new line cord. I'm not sure what the instructions for converting my
>dust collector to 220 said; they were incomprehensible and bore no
>relation to the wires in the junction box. I hope I did it right.
>
>Thanks for the comments; I learned some things that were well worth
>learning.
>
>Ray
>
> Ray Gibbons Dept. of Molecular Physiology & Biophysics
> Univ. of Vermont College of Medicine, Burlington, VT
> gibbons@northpole.med.uvm.edu (802) 656-8910
>
Jon Comments:
Sorry for getting a bit rigid on my initial reply, but electricity and code
violations are a sore subject with me. I can't defend the logic behind some
of the code, nor will I claim that code is the only way to do the job. But
please realize that code is there to keep the homeowner, your local
electrician, and others who not know much about electricity, out of harm's
way. Follow the code and you don't need to know anything about electricity
- that's the way it works and people stay safe. Know something about
electricity and don't follow the code and you have a ticking time bomb.
I, along with a few dozen other families, was burned out because some
a..hole decide that he could run the ceiling flourescents (277 volt) off a
480 3 phase Y by running the black wire to the blue wire and the white wire
to the EMT gound. It worked OK for a while -- until the EMT was spliced
with BX and the ground was interupted because the BX to EMT union was a bit
sloppy, so he fixed it with tape - (made the EMT bigger). The return path
was now through the fixture itself, the suspended ceiling grid, and so on.
Fire - big time! Yeah, the jerk was an electrician (according to the his
military records), knew how electricity worked and that the white wire and
ground were all the same! His comment was "Gee, it shoulda worked!">
Jon N. LeChevet
The power to tax is the power to destroy.
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