Hi, I need to know how to wire a 220v single-phase outlet safely. I
have a 3-10 lead from a double-pole breaker, but at the outlet (its
duplex) do I just put black to one slot, red to the other, and white
to the center pin? where does ground go? Please help, thanks!

Hello gush, I commend you for taking on this project yourself. It is
fairly easy and you should have no problem. I found this very detailed
explanation that has some good pictures:

http://www.lowes.com/lowes/lkn?action=howTo&p=Improve/220outlet.html

I think some of their suggestions are a little overly cautious, but I
guess they are worried about being sued. Here are some of my thoughts
about their cautions:

When working with electricity always:

Turn off the power.
A VERY GOOD IDEA.
Test the wires to ensure the power is off.
I ALWAYS DO THIS BECAUSE I HATE TO GET SHOCKED. I THINK YOU SHOULD
INVEST IN A CHEAP VOLTMETER IF YOU DON'T HAVE ONE.
Lock out the panel box, so no one can accidentally turn the power back
on while you are working.
IF YOU ARE ALONE, THIS SHOULD BE NO PROBLEM.
Check with local authorities to see if a permit is required.
AN INTERESTING IDEA. NEVER DONE THIS ONE.
Have your work checked by an inspector.
ANOTHER INTERESTING IDEA.
Wear eye goggles and a dust mask.
I GUESS YOU SHOULD WEAR GOGGLES AND A DUST MASK AT ALL TIMES. I DON'T.
To avoid overloading the circuit, consult a licensed electrician.
YOU SAID THE WIRES ARE 10 GA. SO THE BREAKER SHOULD BE 30 AMP.

Before you turn off the breaker you can use your voltmeter to make
sure everything is correct. If you check voltage between the red and
black wires, you should see 220 volts. Between either black or red and
the white wire you should see 110 volts. Also, between either red or
black wire and the green wire (ground) you should see 110 volts.
Between the green and white wires you should read ZERO.

After you turn off the breaker you had better read ZERO in every check
mentioned above. If not, you have a problem and should not continue
until it is resolved.

From here on it is just a matter of connecting the wires to the proper
lugs. Some of the newer 110 volt receptacles have "push in"
connectors. I don't know what your's looks like and you will just deal
with that.

I have found that the screw connectors work best when you bend the
wire around the screw in the direction in which the screw turns to
tighten. This way the wire stays under the screw head better.

Since you have a voltmeter, it is always a good idea to test the
receptacle after you have turned the power back on.

I think this should get you safely through the project. However,
should you run into a problem just ask for a clarification and I will
try to help. Here is my disclaimer: I AM NOT A LICENSED ELECTRICIAN.

Work safely, Redhoss

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Request for Answer Clarification by gush-ga on 09 Nov 2005 09:42 PST

Hi Redhoss, Thanks for the info, I'd actually seen the Lowes page, but
it doesn't explain what I need. They are assuming I'm wiring to a
four-prong receptacle, like for a dryer or range. I'm wiring 220v
receptacles for shop use, which only have three holes, like a normal
110v grounded outlet. I have four wires, an three screws! I have two
hot (black and red) one neutral (white) and one ground (bare), but on
the plug itself I have two screws on either side for hot, and a
break-off tab between them, plus a grounding point. I know neutral and
ground are joined at the breaker box, but is it safe to put them both
to the grounding pin on my receptacle, or should I just use ground,
and if so, isn't that an unsafe return path for the 220v? If I use the
common (white) as the ground pin, isn't that against code? That's what
I need help figuring out. Thanks!
/Gus

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Clarification of Answer by redhoss-ga on 09 Nov 2005 10:06 PST

Sorry we didn't get it the first time. The ground wire should be
attached to the metal box the receptacle is mounted in. If the box is
not metal, it really serves no purpose and can be clipped off.

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Request for Answer Clarification by gush-ga on 09 Nov 2005 15:31 PST

wait, but does the neutral or the ground wire go to the
third/center/round pin on the outlet? Thanks!

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Clarification of Answer by redhoss-ga on 09 Nov 2005 16:13 PST

I say the white/neutral wire goes to the "third/center/round pin".

Redhoss has given you very good information, and I am sure that he
will continue to do so.  But I just wanted to comment about "white"
(neutral) and "bare" or sometimes "green" (ground or if you are in
England, earth) wires.

The National Electrical Code is very clear about this:  You ONLY are
allowed to connect the neutral with the ground at the box!  And
nowhere else!  This is an extremely important safety provision.

Now as to your receptacle:  As you note, two terminals (for the flat
blades, probably) are both described as hot.  You should connect one
hot wire to each terminal.  The voltage between these two wires is 220
Volts.

The neutral wire is not needed.  For safety's sake, put a wire nut on
it so the wire is insulated.  (For the record, the voltage between
either of the hot wires to the neutral will be 110 volts.)

You do not mention it, but at the breaker box you need a "ganged"
breaker.  That means that if either hot wire sees too large a load,
both hot wires are disconnected.  Again, this is a very important
safety feature.  I cannot easily describe a ganged breaker, because
styles vary.  You would have to have someone actually look at your
box.

Redhoss has made a serious error in his reply.  If the box is plastic,
the ground wire MUST be connected to the green screw on the
receptacle.  This ground is the third (roundish) opening that you see
on the face of the receptacle.  It is the thing that helps protect you
if a chafed wire should contact any metallic part of the machine you
have plugged into the outlet.

And again, don't mistake the "neutral" wire from the "ground" wire.

Thank you for your information, Liner! My neutral goes all the way
back to the substation, I'd guess (it definately doesn't connect to a
grounding point anywhere in my workshop, including my main panel)..
either way, it tests 0 volts against the earth wire, and 120ish
against each hot wire. In my new outlet, I have freshly-run 12-3 with
two hot, one ground, and one neutral, coming from my shop-area
subpanel which has a ganged 20a two pole breaker for each duplex
250v/20a outlet. What a mouthful! So I'm good up to the outlet, and I
just want to know if I put the earth to the center pin, or the neutral
to the center pin on the outlet. I am guessing earth, but then where
does the current "return" to?

First: ATTACH THE EARTH (EITHER BARE OR GREEN) TO THE GREEN SCREW ON
YOUR RECEPTACLE!!!!  (I apologize for shouting, but this is absolutely
necessary.)  I must respectfully disagree with Redhoss in this
respect.  **IF** the screw is green, or it has "gnd" written near it,
it is ground/earth.  It is definitely not neutral.

If the screw is not green but white/silver, **THEN** it is a neutral,
and you would put your white wire there.

But if you are using a flat-blade, 220 outlet, where the two openings
are in line (as opposed to the parallel version for a 110 volt outlet)
then it is certainly a ground.

Then: ?Dead end? your neutral.  You don?t need it.  But for safety?s
sake, put a wire nut or other insulation on the end.

Now for your simple question about where the power goes.  Well, the
answer is straightforward, but the reasons ain?t.  Let me explain.

It all goes back to Tom Edison.  He not only invented the light bulb
(or did he??there is argument about that), but he invented/engineered
the whole concept of electric power distribution.  But Tom decided
that direct current, such as comes from a battery, was the way to go. 
His original concept was to supply 100 volts to the customer, so he
came up with the concept of two wires, one connected (in effect) to
the ?+? side of the battery and the other to the ?-? side.  He also
decided that it was useful to connect the negative side to the earth.

But some people needed more power.  So, consider two batteries in
series (like in many flashlights).  Pretend that each battery puts out
100 volts.  Measure from the point that the two batteries touch: One
terminal will be +100 volts, and the other will be -100 volts.

If you connect something across the ends of the battery (again think
of a flashlight), current will flow from the positive end of the
battery through the equipment to the negative end of the other
battery.  If you have a wire coming out of the point where the two
batteries touch, no current is flowing.

So, Tom sent three wires to the customers.  Those that needed 100
volts could take power from either hot wire plus the neutral.  Those
that needed 200 volts simply took the power from each hot wire and
ignored the neutral.

When we switched to AC (alternating current) power, the electric
companies kept this scheme in operation.  So, if you need 110 volts,
you choose any hot wire plus the white neutral.  If you need 220
volts, you choose the two hot wires and ignore the neutral.