Screwy wiring on a 3HP, 10-inch table Saw

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  #1  
Old 02-09-14, 05:34 PM
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Screwy wiring on a 3HP, 10-inch table Saw

I bought a Craftsman 10-inch table saw from a retiring cabinet maker, an old gentleman who had replaced the 3 HP motor on the saw several times since he bought it in the Sixties. It is belt driven, old school solid, cast iron top and extensions, in beautiful condition. He actually came out and said "Goodbye, old girl" to her in sitting the bed of my truck before I drove away.

It has a standard 110V plug coming from the motor, but he warned me that he has it wired to plug into a 240V receptacle. There's no ground wire involved here, just two hots and a neutral white wire.

I want to wire it in my outdoor shed, and at first thought of putting a 4-prong cord on the motor and then a matching 4-prong receptacle, but it occurs to me that maybe I can do just fine with 110V (rewiring the motor, of course) and giving it a dedicated 30 amp line. I don't do heavy duty sawing, mostly fine, light parts in quantity.

I'm preferring this method because I have a small wood chipper that will run just fine on this same plug, taking turns with the table saw.

Anyone see any drawbacks to running a 3HP saw on 110V, 30 amps?

Thanks,

Antifa
 
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Old 02-09-14, 05:56 PM
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It has a standard 110V plug coming from the motor, but he warned me that he has it wired to plug into a 240V receptacle. There's no ground wire involved here, just two hots and a neutral white wire.
That would be a 120 volt plug, not 110. There is no neutral required for a 240 volt motor so the white wire is probably being used as a ground wire.

Anyone see any drawbacks to running a 3HP saw on 110V, 30 amps?
I don't see a problem, but you'll have to change connections at the motor (IF it is a 120-240 volt motor) and purchase the proper cord, 30 amp plug and 30 amp receptacle. You must have a subpanel in your shed.
 
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Old 02-09-14, 06:32 PM
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Hi Joe;

Sorry, 120V of course.

Yes, the motor I have already researched with the manufacturer, and they can be wired either 120V or 240V. They come standard with a 120V 3-prong plug and cord, like any power tool, and a recommendation that they get a minimum of 20 amps all to themselves.

The old gent said he just went in and wired it for 240V using the 120V plug. I have no interest in being around an ungrounded 240V anything. Like Russian roulette, it only takes one incident.

Having to put a subpanel in the shed adds to the nuisance and expense of keeping it at 240V. I think that pretty well decides it for me. I'll give it 120V and 30 amps with a good ground.

The shed is actually under the back deck, and right through a cinderblock wall from the main panel of the house, so the wiring run is pretty short.

Thanks,

Antifa
 
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Old 02-09-14, 06:44 PM
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There's no ground wire involved here, just two hots and a neutral white wire.
3-conductor service cord would have a white, black, green. If you have white, black red, then someone cut off the green. If you are calling green hot it isn't supposed to be.
 
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Old 02-09-14, 07:28 PM
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Nope, nothing's been cut off. Coming off the motor is a standard power tool cord just like you'd find on your router or drill. It has black, white, and green wires connecting to the motor, and these to an encased 3-prong plug.

The old gent used the black and white wires for power -- 120V each -- and the green wire as his white wire/ground. It's a simple matter to return the motor wiring to using black for 120V power, white for neutral, and green for ground.

The manufacturer sent me a diagram showing the two different wiring schemes for this 3HP motor.
 
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Old 02-09-14, 07:34 PM
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The old gent used the black and white wires for power -- 120V each -- and the green wire as his white wire/ground.
No. A 240 volt motor does not have a neutral. Black and white is hot and green is ground.
 
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Old 02-09-14, 08:27 PM
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3HP table Saw

What is the Full Load Amps on your 3 HP motor? I find it hard to believe it's in the twenty amp range. The NEC shows 34 Amps for 3HP 115V although the nameplate rating would be different. Will 30amps be enough or should you be using 240V?
 
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Old 02-10-14, 07:06 AM
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Whether wired for 120 or 240 of course the power consumed will be the same--but the behavior will be different. Feed it 240 and the blade will spin up instantly and be much more able to rip through thick or wet wood. At 120 it will act anemic.
 
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Old 02-10-14, 07:33 AM
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The manufacturer sent me a diagram showing the two different wiring schemes for this 3HP motor.
But.....did the manufacturer tell you what wire size you'll need for a 120 volt circuit. The Square D motor data calculator says you would need #8 wire with a 50 amp dual elemnet time delay fuse or a 70 amp thermal circuit breaker. You'd also need an 8-3 cord that I'd bet you do not have.

I'd leave the motor connected for 240 volts or get a lower HP motor. At 240 volts, the circuit can be installed with #12 wire with a 25 amp dual element time delay fuse or 35 amp thermal circuit breaker.

Single Phase Motor Data
 
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