Replies

1. 
   jhausch | Jul 10, 2003 12:07am | #1

   Please be careful with what you are doing.  If you have a neighbor or friend with some household wiring experience, please call them.

   With that said, assuming you are in the US and have a panel with circuit breakers (not fuses), you have 240V single phase coming into your house.  That consists of 2 wires coming into your panel with "power" on them; a Neutral, and a Ground. 

   If you take the cover off your panel, you will see these two "power wires" going into the main disconnect breaker in the panel.  If you put the probes from a meter on those two incoming lines - like on the lugs that hold the wires (with the meter set for AC and the range set to Auto or any number over 250).  You will get something around 220 to 240 volts.

   The neutral and ground wires are connected to buss bars elsewhere in the panel, and those two bars are connected to each other (but this is only the case in the panel) If you take one of the probes and touch it to the neutral bar with the other still on the one of the power wires, you will get 120 Volts.

   Now take a look at your breakers.  the slimmer ones only touch one of those "power" lines when snapped into the panel.  The "double-thick" ones touch both of the "power" lines. 

   If you follow a wire in the panel coming in from something like a bedroom, you will see that the Black goes to the breaker, white to neutral, ground to ground.  That is a 120V circuit.

   If you follow the lines from a dryer or a stove, that should probably go to the thick breakers, has no neutral, but still has a ground.  That is a 220V circuit.

   If you want to wire 220 to your saw, you need a 220 breaker in the panel and a dedicated cable run from that breaker to the saw (or to a special 220V outlet/receptacle for the saw) .  

   Whatever color of wires are connected to the 220V breaker, those get connected to your motor's "black and red" (as written in your post).  The Green is always the ground and is connected to the green, or the bare wire, and that is probably connected to a ground screw in on the motor case itself.

   Like I said, be careful.

   Steelkilt Lives!

   
   

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   Edited 7/9/2003 5:08:50 PM ET by Jim

   
   

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   Edited 7/9/2003 5:10:23 PM ET by Jim

2. 
   johnhardy | Jul 10, 2003 12:34am | #2

   I'll second Jim's post but add a caveat that if you haven't done lots of wiring (sounds like you haven't), you should *not* attempt to add a 220 volt circuit and associated wiring. Please call a licensed electrician and do this properly. A little money saved here could have dire consequences if what you do isn't done correctly ... like kill somebody.

   I've done lots of wiring and this isn't complicated. But I was taught by a high school buddy who was licensed and I do it *the right way* and it's as good as a pro does. Not everything I've seen in my days has made me feel good. Maybe nobody got hurt, but that was only because of luck.

   Note that you can't simply change the circuit you're talking about to 220 volts. There are undoubtedly other outlets on the circuit and you'd screw those up. The 220 volt line needs to be decicated, and it needs to be a new circuit.

   John

3. 
   JohnWW | Jul 10, 2003 12:38am | #3

   If you're saying that the wall box has a black, a red, a white, and a green wire then the answer is simple, presuming that whoever did the original wiring followed the standard color coding.

   The white wire is a neutral and is used for 120 volt wiring only. Since you won't need it for wiring the saw, just screw a wire nut onto it and leave it in the box.  Don't cut the neutral wire off short before you cap it, somebody, someday may need to use it.  After that the rest is easy, the black goes to black, the red to red, and the green ground wire goes to the green in the cord.  Actually the red and black are interchangeable, if you hooked the black in the box to the red in the cord the saw would work just the same.

   You don't say why you are making the changeover but unless the wire sizing in the wall is inadequate for running the saw on 120 volts you won't notice much of a difference in the way the saw runs.

   Alternating current cycles from positive to negative and back again 60 times per second in the U.S.  In a single phase hook-up there is just one lead coming into the machine with the current cycling this way.  In three phase, three wires bring the power in, all of them cycling at 60 cycles per second, but the cycles are out of step with each other by a third of a cycle. 

   The big advantage to three phase shows up when it is used to run a motor.  A single phase motor needs internal switches and extra field coils to get started, three phase motors don't need these extra parts for starting, making them simpler, sturdier, and less expensive to build.  I'd guess that at least 90% of the problems with single phase motors is with the starter circuitry causing problems, which often lead to the motor becoming heat damaged. 

   A three phase motor also starts with more power, and once going runs much more smoothly and efficiently.  An added advantage is that a three phase motor can be reversed instantly, this generally isn't a feature needed in woodworking applications but it has a lot of use in industrial machines.

   If you have a three phase machine but only single phase power, you can buy or home brew a converter that will allow you to run the machine off single phase power.  Most power companies won't bring three phase power into a residential home without giving you a lot of hassle and a much larger monthly bill. 

   John W.

   P.S.  Since I started writing this two more posts showed up both warning of the risks of do-it-yourself wiring.  You can do this yourself but you do need to be careful or you could get badly hurt.  If you really aren't clear about the basics of wiring it may be more than worth it to get someone with experience to help.

   
   

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   Edited 7/9/2003 5:47:57 PM ET by JohnW

1. 
   johnhardy | Jul 10, 2003 03:14am | #4

   JohnW is not being as clear here as he should have been.

   Just because there is a black and a red wire in the box you shouldn't jump to the conclusion that there is 220 volt current there. Somebody could have used romex (12/3 with ground or 14/3 with ground) for a lighting application and the red and black could both be hot wires from the same pole ... i.e., no 220 potential. Worse, there is no guarantee that this is the only receptacle on the circuit.

   Please do not attempt this yourself. A little knowledge can be a little problem or a big problem. In electrical applications, it is almost always a big problem. I wouldn't dream of changing the brakes on my car for fear of killing somebody because I screwed up. But I'd rewire your house in a millisecond because I know I wouldn't make a mistake.

   Hire an electrician or get someone who knows how to do this properly before you proceed further.

   John

2. 
   vincent843 | Jul 10, 2003 08:18pm | #5

   Hi,

   I'm sorry that did not make it clear at first. Originally, this is the 220v circiurt for the stove( #6-3), since I don't use it, I run the cable to the garrage as the sub pannel. From the main pannel it has the 50 amps double breakers. From the attic, where the wires had pulled off from the kitchen, I extend the #6-3 thru a junction box to the garrage. The box from the garrage now has 4 spaces, 2-20 amps single used for the plugs around the garrage, the last 2 , intend for 20 or 30 amps double breakers for the saw. I haven't run the wires for this outlet yet( that is why the question was asked). So, as I understand, I don't need to run the white wire to the saw. Please, fill me more inputs as I'm happy to take it. Also, note that the green and white from the sub box are isolated. Thanks. vn.

1. 
   BarryO | Jul 10, 2003 08:46pm | #6

   'sounds like you're doing fine so far.

   The stove uses both 240V and 120V, so it had a 240/120 circuit, with 4 wires.

   Your TS is 240V-only, so the white neutral wire is not needed.  You can just wire a 3-conductor 240V socket, as opposed to a 4-conductor 240/120V socket.  For this circuit, you can run 10-2 w. romex rather than 10-3.  Just wrap the white wire on both ends in red tape, to signify it is a hot wire rather than a neutral.

2. 
   DouglasABaker | Jul 10, 2003 09:14pm | #7

   Unless your subpanel is installed correctly (which, no offense, I doubt it is based on the questions you are asking about a 240V circuit), you are leaving yourself potential for trouble.

   While electrical wiring is not rocket science, it does take a fair amount of detailed knowledge and experience to get right.

   What I'm primarily concerned about is the ground on your subpanel, and whether or not you removed the connection between the neutral and ground bus (which you should have).  While they are connected in the main breaker box, they should not be in a sub-panel.

   Following on to that, your question about wiring a 240V outlet, ASSUMING YOU ARE WIRING A NEW OUTLET, is easy: 1.  Black in panel gets connected to 1 leg of 240V breaker 2.  White in panel gets marked as HOT (usually with black tape) and is connected to other leg of 240V breaker3.  Green/Copper in panel is connected to Ground Bus (NOT neutral).4.  At the other end, connect the black to one side of the 240V outlet, the white to the other (after you also mark IT as hot, of course), and the green to the ground on the outlet AND the box.5.  Wire the plug on the saw up to match the outlet.

   If you decide you want to protect for a 120V/240V outlet (for whatever reason), then instead of WHITE in the instructions above, use the RED.  In the breaker panel, wire the WHITE to the Neutral Bus (NOT the ground), and in the outlet box, put a wire nut on the white and tuck it away in the back of the box.  Note that this requires 4 conductor wire as opposed to the 3 conductor used above.

   That is how a 240V outlet is installed - nonetheless, from the questions you asked, I would urge you to call an electrician.

   One other point here - if this is an EXISTING outlet, then you need to make darn sure that the red and black are both actually hot, and that one isn't being used as a "traveller" for a light switch.  You also need to make sure that the red and black are not off of the same leg in the breaker box itself (which could occur if they were designed to run two different 120V circuits).

   d-

   Edited 7/10/2003 2:33:11 PM ET by DM_Woodworking

   Edited 7/10/2003 2:35:26 PM ET by DM_Woodworking

1. 
   vincent843 | Jul 10, 2003 11:50pm | #9

   Hi,

   I hate my guts but want to try again. Here we go, from the main, black and red go to each legs of the breaker, white to nuetral bus and green to ground bar. In the attic, from the junction box, same size of wires #6-3, color to color. To the sub, black, and red go to their own post, neutral(isolated from ground) to the neutral bus,last is green to the ground bar. Now, from here, a double breaker installed, #10-2, black and red to ech leg of the breaker and the green to ground termial of the outlet. Hope I am not missing anything.Thanks. vn.

1. 
   rodknee | Jul 11, 2003 03:24am | #10

    Hello all, this is my first post, very helpfull site.  But anyway, in addition to all the  things these other fellas have stated, make sure you use the correct size breaker. You probably know this already but for safetys sake.  Your table saw should have an electrical ratings plate on it telling you how many amps you TS draws.   For number 10 wire a double pole 30 amp should suffice.  However, the ampreage draw generally should not exceed 80% of your breaker rating. You know, just in case there would be some sort of surge in your power.  So, for a 30 Amp double pole your TS shouldn't call for more than 24 constant Amps when in use.  But I can't imagine that your TS would draw more than that.  But hopefully that helped a bit, probably just stating the obvious, but anyway :-)

                           Rodknee

2. 
   DouglasABaker | Jul 11, 2003 04:26pm | #11

   You do not use 4 conductor wire for a 240V outlet - you only use 4 conductor for a 120/240V dual voltage outlet.  So, you really should only be using 3 conductor, in which case white and black would be hot going to each side of the 240V outlet, and green is ground - there is no neutral.

   If you definitely want to protect for dual voltage (I never have in any of mine, but I don't think it will hurt anything), then yes, red and black go to each leg of the breaker and to each side of the outlet, the white goes to the neutral bus and gets capped in the outlet box (it isn't connected to anything), and the green goes to ground bus and to the ground on the box AND the outlet.  This is definitely unconventional however - you generally should use the correct number of wires...

   Also, make sure you are using the appropriate size wire for the length of run and the amperage.  For a short run, 50' or less, and a smaller breaker 30A or less, 10 ga should be fine.

   Doug

3. 
   johnhardy | Jul 11, 2003 07:03pm | #12

   You *do* use 4 conductors for some 220 volt outlets. For a tablesaw, you'd only use three, as you've described. Some devices, such as an electdric dryer or an electric oven, have 120 volt timers and such so those 220 volt outlets could have four lugs and four prongs on the plug. Two for the hot legs, one for the white, and one for the green.

   Since the circuit in question had four wires, and I think it was for a dryer, I'd leave the white alone and cap it in the outlet box, as suggefsted. This would allow for more flexibility in the future.

   John

4. 
   DouglasABaker | Jul 11, 2003 08:11pm | #13

   Re-read my previous post, which I will summarize here for you:

   You *DO NOT* use 4 conductor wire for a 240V outlet.

   You *DO* use 4 conductor wire for a 120/240V dual voltage outlet. 

   A stove or dryer with a timer is a 120/240V outlet, NOT a 240V outlet - if you don't think this is the case, try and plug a 4 prong (dual voltage) plug into a 3 prong (single voltage) outlet.

   We can chalk it up to a semantic difference if you'd like, but there is a very real difference between 120V, 240V and 120/240V circuits.

   Doug

   Edited 7/11/2003 1:13:54 PM ET by DM_Woodworking

5. 
   johnhardy | Jul 11, 2003 10:55pm | #14

   Sorry for the confusion. We are on the same page here.

   My main concern is that somebody who doesn't understand wiring be extremely careful in making a changeover. Having it done properly is money well spent.

   John

6. 
   jhausch | Jul 12, 2003 02:44am | #16

   I'd like to ask a question on the 2+g vs 3+g wire deal. 

   If you buy a dryer nowadays that has all 220 stuff inside (no need for a neutral/120v power) you are still gonna get a 4 prong cord (unless you specify otherwise) to go to your 4 prong recept, which seems to be code now. . . .I wonder what they do with the neutral in the dryer (connect it to ground, let it float,) ?

   In other words, new houses being built are getting the 4 prong plugs.  If you bring your old dryer to your new home you need to buy a new cord (or change the recept)  In either case you end up with a capped wire somewhere.

   How are the pros handling this?

   (this thread is slowly heading off on a tagent, not officially hijacked yet, but getting there)Steelkilt Lives!

7. 
   johnhardy | Jul 12, 2003 03:40am | #17

   I think lots of dryers have the gound and neutral tied together, which makes me somewhat nervous. I'm more comfortable with two hots, a white, and a ground wire. To get more technical information you'd probably have to post over in Fine Homebuilding. But in a nutshell even with a three prong plug the dryer is still using 120 volts for the timer and is doing so by using the ground as the neutral (at least what my understanding is).

   John

8. 
   DouglasABaker | Jul 12, 2003 07:03pm | #18

   I can safely say that I have no idea what they do with the neutral.  I would guess (but that's all it is) that it is just a 2 + g cord with a 4 prong plug on the end. 

   To be completely honest, I'd be surprised if there is such a thing as a 240V only dryer any more - every one I've seen recently has a timer of some sort on it (and that stuff is all 120V).

   d-

3. 
   watkinsjd | Jul 10, 2003 09:21pm | #8

   Vincent,

   I feel obligated to add to the other respondents who advised you to seek professional help.  From what you have said it doesn't seem you have enough knowledge to be sure the job is done safely. And, it is a difficult task to educate anyone sufficiently to do this task safely via posts to Knots.

   If you couldn't figure out the purpose of the white wire by tracing it back to the source, you probably need more knowledge than you are going to get from Knots.

   Electrical fires are way too common to take the risk.  We are not just talking a fried motor here but potential loss of life.

   John 

4. 
   JohnWW | Jul 12, 2003 12:36am | #15

   A couple of off hand references have been made in this discussion to the sizing of circuit breakers and I think a misunderstanding needs to be cleared up.  The purpose of the circuit breaker is to protect the wiring in the wall from becoming overloaded and causing a fire. 

   A circuit breaker is sized to protect the smallest gauge wire in the circuit it protects.  If the wiring is old and goes through several boxes determining the smallest wire in the circuit can be a challenge, ideally it is a straight run and all branches are the same gauge as the main run. 

   The proper size breaker is set by the electrical codes, factors beside wire gauge taken into consideration include type of insulation on the wire and ambient air temperature.  You can, of course, use a lower amperage breaker if you want to, but you should never just size the breaker to the draw of the machine.  To protect the machine, if you think it is important, you should install a motor switch that includes a fuse or breaker that is matched to the motors draw.

   John W.