View Full Version : 240v table saw conversion - HELP!
07-28-2002, 04:17 PM
OK so I decided to convert my table saw to 240 and give it it's own circuit in my wood shop. Pretty easy to do since the breaker box is right in the shop. I bought (at the recommendation of the Home Depot guy) the following to do this job:
1. 12 gauge wire. Rubber wire with black (hot), white (hot) and green (ground). Not solid copper wire, but stranded.
2. A single pole 15 amp breaker.
3. A 20 amp 250v outlet. And a plug to fit it.
I ran the wire and connected it to the outlet first. I then connected it to the breaker. I connected both hot wires to the same 15 amp single pole breaker. I then switched the 2 wires in the motor housing exactly as the owner's manual said to. I plugged in the saw, flipped the breaker and tuned the saw on. Nothing happened. I tried a different breaker and still nothing. I tested the circuit with a tester and it will tell me that I've got a complete circuit, but if I switch it to 250v AC and plug it in to the outlet I get nothing. I think this tells me that I don't have power to the outlet. I know the wire I ran is ok because I tested it. The breaker is ok as well since it works on other circuits. I wonder if I need a different breaker for this application. I asked the HD guy and he said this should work, but I don't think I'm talking to a master electrician. Could someone please tell me if I'm on the right track and what I need to change? This is pretty frustrating.
07-28-2002, 05:26 PM
I'm REALLY not the wiring whiz around here... but, as my faded memory recalls, "I connected both hot wires to the same 15 amp single pole breaker" is your problem. 220 requires a Black Hot, a Red hot, and a nuetral or ground, which requires a double pole breaker.
If I'm wrong, I'll learn right along with ya... I know how to hook up a shop (been there, done that - 3 times!) but I don't know the terms worth beans...
07-28-2002, 07:07 PM
Marc is close. You won't need a white neutral wire for this task.
You will need to get a 220 double pole breaker (get the same brand as your others or they won't fit in the box) This breaker has two hot terminals. You need to put the green wire to the ground in the box. The white wire should have a wrap of black tape on the end of the wire so that some one else will know it is a hot wire. (With a normal wiring this would be a red wire). This black wrapped white wire to one of the hot terminals and the black wire to the other. This will give you 240 volts at your saw.
Make sure you have the jumpers in the motor set right and you are there.
For general interest three wires come to the house. Two hot wires and the neutral wire. Between the neutral wire and ether of the hot wires you get 120 volts. Between the two hots you get the 240
120 Volts |......................|
__________________Neutral........| 240 volts
120 Volts |.....................|
Hope that helps
07-28-2002, 07:09 PM
Marc is right it takes 2 breakers but they als9o need to be on different legs of the power. You should have 2 hot woires coming into the breaqaker box. On my box the power leg is changed every other full size breaker installed. So when I wired my saw the breakers on next to each other and on the same side, but they are on different power lines coming into the shop. I am sorry it is much easier to see than describe. When Sonny takes a break from his grand kids he will set it streight for you. He did for me.
Good Luck :)
07-28-2002, 09:27 PM
Thanks guys. I have another question... I looked at the double pole circuit breakers and noticed that they say 15 twice - one for each pole. I'm showing my ignorance here, but is that truly one 15 amp circuit or 2? And if it's 2, do I need a breaker which takes up 2 slots and has only one switch on it? Or is that really the same thing? I'm just trying to be very careful before I set my house on fire or ruin my table saw or something. Thanks again.
07-29-2002, 02:40 AM
Yes the 240 breakers have two breakers tied with one switch. Each brand has a different method of doing this. But you need both sides to trip if one goes out. That way you are not hanging 120 to ground on one side it you trip the breaker.
07-29-2002, 05:28 AM
Go get one of those Sunset books like "Electricity Basics" or "Basic Wiring" ...something like that... It'll really help you understand...well, the basics!
07-29-2002, 06:02 AM
Hey Wood ,...........Lou is right on the money
He is our resident EE
Sonny is our resident maintenance guy
I try to keep'em both straight
Go look at my explanation of how a dual voltage, dual winding motor works..................in "I'm New to Woodworking" forum, under "Want to use 220volt..........." its down on page #2 now. There are other factors involved but that is a thumbnail explanation of what you yourself are doing......................dick again
07-29-2002, 08:58 AM
Lou, you're the greatest. Thanks for your help. I'll have it wired up in no time now.
07-29-2002, 09:11 PM
I got it wired tonight and it works great! The saw has never cut better. The guy at lowes told me to wire it with a 20 amp breaker or I would trip the breaker every time I put a load on the motor? Is that true? The breakers were like 7.00 so I got 2 of them, a 15 and a 20. I used the 15 to test it on some scrap pine tonight and it worked well, but I wonder if I should install the 20 for times when I'll be loading the saw down with some serious hardwood. I've never really had a problem before, although I've never ripped purpleheart either... Thanks for everyone's help!
07-29-2002, 09:26 PM
That depends on the motor on your saw. Just so you know, when you go from 120 to 240 you cut the current in half. A typical 2 hp motor uses 20 amps at 120 and 10 amps at 240. You want the load at no more than about 70% of the rating of the breaker and the wire. Your 12 gauge wire is rated to take 20 amps. You don't want to run more than about 15 amps on that wire. If your saw is 1 or 1 1/2 hp your current requirements will be 5 to 8 amps for the table saw alone. At that you shouild never trip a 15 amp breaker.
All that being said I would use the 20 amp because that is the wire you have and the plug. It is ok to use a breaker less than the wire rating but not more. I would not tell you to go buy a new one but since you have it use it.
07-29-2002, 09:29 PM
I think I fould the answer in another post. (yes I do use the search function) It looks like I will be fine with a 20 gauge circuit as long as I have heavier wire. I believe 12 gauge will support 20 amp correct?