New table saw (110v, 15amp, 2hp)

[Gargoyle]

I just need some affirmation on my assumptions and what I've been told by other amateurs.

I just bought a new table saw and I'm building my workshop in the basement. The table saw is set for 110v 15amps but says it can be switched to 220v. When I run the tablesaw on the existing 110v 15amp outlets, the one light that I have plugged into the same circit dims when I start it. I would like to put the saw on a 220v circit so I don't get that dimming and the saw starts easier and faster.

Am I correct in assuming that if I double the voltage going to the table saw, the amperage requirements get cut in half? Therefore the table saw will draw 220v and 7.5 amps? If this is the case then the breaker I need would be a 220v 15amp or 2 pole 15amp breaker right?

How is this breaker installed? Just 2 110v 15amp hots onto the new breaker?

[HayZee518]

Yes, you got it! Check the re-wiring in the motor. There may be wires or links to change around for 220 operation. As voltage goes up, the amperage is halved. Use a two pole 15 breaker. White to one side, Black to the other and the yellow/green or green to earth (equipment) ground.

[Rewired]

Yes you are correct about the current draw of the motor, it will be roughly 7.5 amps, and as well the starting current the motor draws will be half of what it would be on a 110V circuit.
You are also correct about using the 15 amp 2-pole breaker, it will clip in the panel just like any other breaker, but it will sit across TWO "poles" of the panel to give you the 220V. Both "hots" of your new cable ( you need 2-wire cable) go onto the breaker and depending on the length of your run, I would use no smaller than #12 to feed it.. #14 would work in most cases, but the thicker the wire is (to a point), the less the voltage drop is especially during startup, and in turn, its a lot easier on your motor.

A.D

[Gargoyle]

Thanks! Just one clarification. You say white to one side and black to the other ... are you meaning 2 blacks to the other? the breaker panel has one main 100amp breaker. Will there be 2 110 lines coming from that into the 'belly' of the box. And in that case would I take a hot(black) from each and put them into the new breaker? Can you go into just a little more detail as to what I will need to do in the panel?

Thanks again!

[Gargoyle]

Okay, that helps further. I have about 20 - 30 feet to run and I've bought 30amp rated indoor house cable for it. I would assume this is #12 if it's rated for 30amps.

[HayZee518]

#12 is rated for 20 amps, #10 is rated for 30 amps, #14 is 15 amp. #12 SO or SJO is sufficient for the cable. You don't have to worry about voltage drop until you reach 100 feet or more. In that case it's supposed to be no more than 3% per 100 feet.
Question: Is the saw from Harbor Freight? If it is I have a ten inch just like it. Also dual voltage motor.

[LazyPup]

The motor is rated at 110v @ 15amp. However, that is the full load amp rating of the motor.

Motors also have a LRA rating, although it is not commonly listed on motor data plates, LRA is Locked Rotor Amps and is a momentary surge of energy necessary to overcome inertia and start an armature in motion.

Normally the LRA is 3 times FLA. LRA is momentary during start, and as soon as the armature starts moving the load will drop back to the FLA rating.

Circuit breakers are designed to tolerate the momentary surge of LRA current, however, the increased load is what causes the lights to dim during the start.

Converting the motor to 220 would be one solution, but I dont think i would opt for that. The problem is that once the motor has been converted to 220 in dedicates the saw to that circuit only. It would make it very difficult to move the saw to another location for temporary use on a project.

I think a more practical solution would be to install a dedicated 110v 20 circuit for the saw. The wiring, breaker and installation would be easier and cheaper as well.

given that wattage is voltage x amps and we buy electric utility by wattage there would be no economy in changing the motor.

110v x 15a=1650 watts
220v x 7.5a= 1650 watts

[Gargoyle]

HayZee518: It's a General 50-185 10-inch.

LazyPup: A great suggestion, I just wish I had have checked this forum about 2 hours ago to catch your post. I've already run two outlets on 220/15. I haven't yet installed the breaker, the local home depot didn't have Seimens breakers and since I had other things I could be doing in the shop, I figured I'll look around tomorrow at a couple more stores. I figure it doesn't hurt to be picky and get the same brand of breaker that's already there. As for the outlets, I do plan on buying a planer and jointer in the near future so they won't go without use, and I'll have all my toys on a single breaker this way. I don't expect that more than 2 tools will ever run at once, my shop isn't that big

[LazyPup]

I am sure Hayzee, rewired or one of the other guys can perhaps explain it better than I but in my understanding, the singular advantage of putting heavier loads on 220v in to insure a more balanced load on the Main breaker.

Given that you have already begun running the 220v service thats great.

You stated that your planning to buy a jointer and planer. It is highly unlikely that you would have to move those machines for other projects so you might be ahead to consider either getting 220v motors or getting motors such as you have now that can be converted, and running that equipment on the 220 to balance your load.

[Gargoyle]

The table saw that I have is already capable of handling 220v, all I need to do is switch the plug to a 220/15 plug and open the starter panel on the motor and switch the marretting of 6 wires based on a supplied diagram. Pretty simple. And I would be sure that the additional equipment I purchase has the same capability.

Thanks alot, everyone, for your help!

[HayZee518]

Only real reason for the higher voltage running is efficiency. The motor will run cooler with less amperage draw and motor efficiency goes up because of less heat generated.
In some places you'll find flourescent lighting wired at 277 volts. They're able to run more fixtures on a smaller wire at the higher voltage, again efficiency.

[Rewired]

LazyPup:

That is one of the main advantages of putting heavy loads on 220V is that it does help to balance the load between the two hot legs of your panel, [u]but because the voltage is doubled, the amperage is halved</u> and you can get away with a smaller gauge wire as well.

I changed around a friend's garage where he had a small metal fabrication shop going.. The Garage was fed from only an old 40 amp stove circuit that he would trip on occasion. After I went through the place and flipped whatever motors we could to 220V, and balance out a few 110V loads he was able to run all his lights, exhaust fan, a pair of drill presses, air compressor and still be able to put down a nice long bead of weld without tripping the 40 amp breaker! line current was like 35A a side, ZERO neutral current with all those loads going SIMULTANIOUSLY!!. Could not believe we got that that place balanced that good! Not bad for a measly stove circuit either eh?

A.D

[HayZee518]

The cordage that you'll use on the saw will have three conductors in it. A black, a white and a green. You mentioned two blacks on the breaker. I have never seen a piece of SO, SJO cord with two blacks in it. However it wouldn't hurt to put some black tape on the white to distinguish it from a neutral. Same with the romex I assume you are using for the branch circuit plugs. Put a piece of tape on the whites at the receptacles. Both screws of the outlet will be brass which distinguishes it from a 110 circuit which has a brass and nickel colored screw.

[Gargoyle]

Getting back to this ... put the whole idea aside for a while.

Anyway, I have run a 2-wire line from the outlet to the breaker panel. For clarification, 2-wire meaning a black, a white, and a completely bare (ground). In the breaker panel, do I put the black lead on one pole, the white lead on the 2nd pole? Then I mark that white lead with black tape to say it's 'hot' to anyone looking in the panel in the future. Now, on the outlet, I just attach the black to one side, and the white to the other? Again taping the white with black to signify 'hot'.

Is this correct?
If not, where am I going wrong?

Also, if I'm using the white's as 'hot' what's neutral? do I not need a neutral?

Thanks guys/gals!

[Rewired]

Gargoyle:
The way you have described wiring the circuit IS correct.
You do not have a "neutral" present here because one is not needed.

A.D