In a message dated 97-11-09 21:45:15 EST, prubrew@ix.netcom.com writes:
> I came by a "new" (about .25 hrs on it) compressor made by Hitachi.
> All of the directions, ID numbers etc. are in Japanese. The electrical
needs are
> easy to make out though, calling for either 200 or 220 V. My biggest
concern
> at this point is one tag which is in english says "220V, 4 pole". I of
very limited
> electrical knowledge, have NO IDEA what this means.
> The cable leading to the on/off switch has four wires coming out, all
> of which are currently fitted with circle end crimp on fittings. The
colors of the wires
> are Black, Red, White, and Green. The Black, Red and White are all
interconnected
> by some sort of resistor thingies, three in all. One between red and
black, one between
> black and white, and one between red and white. The green wire stands
alone.
> (as does the cheese I hear)
> Can someone tell me what these thingies do? How would I connect these
> four wires to a standard three prong 220 plug, such as that used for my
dryer in
> my garage? Or do I need a four prong plug and a new outlet box ? "
Chris:
I may be able to help, but first, a little tutorial!
All modern house wiring in America is of the four wire (4 pole) variety.
Three of the four wires come into your house from the secondary of the
utility company's transformer. The fourth wire is the ground connection. The
secondary of the transformer has a center tap, and is wired as shown below -
| |
| | Primary
| |
ooooooooooooooooooooo
ooooooooooooooooooooooooooooooooooooooo
| | |
Secondary
| _____110V_________|________110V_______|
| | |
| N |
| |
|__________________220V_________________|
| |
H1 H2
There is 110V between the N, or neutral leg, and each of the hot legs, H1,
and H2. Between the two hot legs, there is 220V. The neutral leg is tied to
ground at the service entrance (breaker, or distribution, box) to your house,
and with few exceptions, the neutral is not connected to ground at any other
point.
The neutral wire is ALWAYS white or light grey, The ground wire is ALWAYS
green or a bare conductor. The two hot legs can be any color, but they are
almost always black or red. Standard two conductor w/ground cable comes with
one white, one black, and one bare or green conductor. Three conductor
w/ground comes with white, black, red, and bare or green.
When you wire a 120v outlet, the black wire goes to one of the hot legs, the
white wire goes to neutral, and the bare or green wire connects to the
neutral/ground connection at the distribution box. it is intended that the
neutral carry all return current, and no current is to be carried by the
ground wire. This is a safety feature - the ground wire is to maintain the
conductive portion of any device connected to the outlet at ground, or zero
potential.
When you wire a 220v appliance, using a two conductor w/ ground cable, the
black wire goes to one of the hot legs, the red wire goes to the other hot
leg, and the bare or green conductor is connected as for the 110v outlet.
Sometimes, though, a 220 volt appliance will use 220 volts for the main
function, and 110 volts for the control circuit - timers, clock, relays, etc.
An electric oven is a good example of this. In this case, a three conductor
w/ground cable is used. Black to one hot leg, red to the other, white to the
neutral, and green or bare to the neutral/ground connection. The cloak,
timer, etc, is then connected, internal to the appliance, between the neutral
and one of the hot legs.
In some applications, to save money, the electrical code allows you to use
two conductor w/ground cable for a 220 volt outlet for an appliance with a
110 volt control circuit. This is the only time that the ground and neutral
wires are allowed to be connected anywhere other than at the distribution
box. In this case, the black wire is connected to one hot leg, the white wire
is connected to the other hot leg (and painted red or black in the breaker
box and the outlet box), and the green or bare wire is connected to the
neutral connection as normal. The four wires coming from the appliance are
connected to the outlet as so: black to black, red to white, green or bare to
green or bare, and the white is then also connected to the green or bare
wire. The code allows this for ranges, ovens, and dryers, but does not
mention compressors.
My recomendation, then, would be to run a new 10 Ga.(or larger, depending on
the motor rating) three conductor w/ground cable from the breaker box to the
compressor, and wire it color for color - black to black, red to red, white
to white, and green or bare to green or bare. Inside the breaker box,
adjacent breakers alternate between H1 and H2. As you go from top to bottom,
the breakers are fed alternately from H1, H2, H1, H2, H1, H2, etc. When you
plug in a 220 breaker, it automatically connects one pole to H1, and the
other to H2, so you can't go wrong. It doesn't matter which is which.
When you buy the wire, be sure to ask for three conductor with ground. If you
ask for two conductor, you will get a cable with one black and one white
wire, but no ground. If you ask for a three conductor cable, you will get
red, black, and white, but no ground. If you ask for four conductor, you will
get red, black, white, and some other color, but not green. The ground wire
is always specified seperately. You will need to buy the four wire socket and
plug as well.
That's the first class, guaranteed correct way to wire, and is also the most
expensive. To save a few bucks, you can get two conductor w/ground, and wire
both the white and the ground wire to the cable's ground wire, using a three
wire plug and socket. I'm not sure just how legal this would be, but is is
certainly adequate.
There is one thing that concerns me, though. Since the wires terminate in
ring terminals, I wonder if the compressor is designed to be used with a
magnetic starter, as many of the larger units are. What size is the
compressor? "Magnetic Starter" is a big fancy term for a big fancy relay. Are
you sure the on-off switch is really that, instead of an unloading valve? I
am familiar with how magnetic starters work, but I have no "hands on"
experience installing them. If you need one, instructions should be included
with the starter.
As to the "resister looking thingies," I have no clue as to what they are. I
would suspect, though, that they are surge suppressors. I would not worry
about them, just wire it as above, and let them take care of themselves (I'm
assuming these thingies are located inside an enclosure with the switch,
rather than at the end of the wires?)
I hope this has not been more than you wanted to know, and has been of some
help. If you need more, let me know.
> What have I gotten myself into ?
A world of pleasure! After you have used an air compressor for a while, you
will wonder how you ever got along without one.
Dan Masters,
Alcoa, TN
'71 TR6---------3000mile/year driver, fully restored
'71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion - see:
http://www.sky.net/~boballen/mg/Masters/
'74 MGBGT---3000mile/year driver, original condition
'68 MGBGT---organ donor for the '74
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