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Thread: Running a 220V saw from a dryer outlet

  1. #1
    Join Date
    May 2007
    Location
    Ventura, CA
    Posts
    530

    Running a 220V saw from a dryer outlet

    Greetings -- I have another basic question for the group.

    Have any of you been able to run a 5HP 1P cabinet saw from a 220V, 30-amp (I think) electric dryer circuit?

    The Delta manual says their 5-HP saws need a circuit with "#10 wire and a 40-amp time-lag fuse" so at first blush, it would appear that I'm out of luck.

    The electric dryer circuit in my garage has two 30-amp breakers ganged together. I presume that is only a 30-amp 220V circuit. Hopefully if that is incorrect somebody will let me know.

    I have a line on a used 5-HP unisaw, and I was on the cusp of pulling the trigger on that deal when I double-checked the details on that circuit... so I'm hanging fire. Frankly I'm amazed that the saw requires more power than the electric dryer, but it appears that is the case.

    If I need to run an additional 40-amp 220V circuit I'm probably out of luck due to panel limitations.

    The Delta manual calls for a 20-amp circuit for their 3HP/1Ph saws, so that would be doable.

    If anybody has any thoughts about the viability of running a 5HP/1Ph Unisaw on the circuit I've described, I'd love to hear them.

    Thanks in advance. I hope I haven't exceeded my question quota for the day...

  2. #2
    Join Date
    Mar 2007
    Location
    Binghamton, NY
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    437
    my 5hp Sawstop runs from a 30 amp 10/3 line with a three-blade dryer outlet, 30 amp standard breaker.

  3. #3
    Join Date
    Mar 2007
    Location
    Summit County, Ohio
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    63
    Tom, This seems incorrect to me: "The Delta manual says their 5-HP saws need a circuit with "#10 wire and a 40-amp time-lag fuse" so at first blush, it would appear that I'm out of luck."
    My understanding is #10 wire would be for a 30 A. circuit while 40 A. would require #8 wire.
    If #10 wire is needed you're o.k. with the dryer circuit.

  4. #4
    Join Date
    Jun 2005
    Location
    Trinity County California
    Posts
    729

    Running a 220v saw

    My General TS has a 5 HP Baldor motor. In a newly constructed shop, specs call for 19 amp continuous service on a 30-amp circuit with 3-ply #10 guage wire.

    While the place was being built, the staff at General said I could run the saw on a 20-amp circuit and I'd never see it trip the breaker.

    Gary Curtis

  5. #5
    Join Date
    Apr 2007
    Location
    Phoenix, AZ
    Posts
    1,417
    Check the saw placard for the amps that it pulls. Here are some useful nums:
    1 HP = 746 watts.
    5hp = 3730 watts
    volts * amps = watts so...
    3730 watts / 230 volts = 16.2 amps. You use 230 for elec calcs, as it might be 220 to 240 depending on various power transmission factors etc..

    Various factors are quoted in the NEC for what % of a wire's load you should run on it. However, the "official" numbers are ALREADY derated, both for temperature and load. However, for NON COMMERCIAL, that is non-full-time use, as for instance a tablesaw hobbiest who turns the machine on/off but doesn't leave it running 3-5 hours, 80%-85% are commonly used.
    16.2 amps = .85 X, so X= 16.2/.85 = 19 amps. Therefore, 20 amps wire would work for normal continuous operation... which is 12 gauge wire.

    HOWEVER, when you look on the motor's placard, the AMPS stated will be HIGHER than we just calculated, and this is due to various power pulls under high load, and on start up. For instance, my 3hp PM66 states "15 amps" for 230v. A common electricians rule of thumb is this:
    At 230 volts, a single-phase motor draws 5 amps per horsepower., so 25 amps for you...

    The upshot of it is that I would certainly think a 30 amp circuit run on 10 gauge wire would be fine to run it. Remember, the circuit breaker (30 amp) on the 10 gauge wired dryer circuit is there as a PROTECTION FOR THE WIRE, and so there is no risk to try it. Since a 5HP motor should not pull more than 30 amps, you should be fine.

    The use of a 40 amp fuxe/CB on 10 gauge wire is incorrect per the NEC, and would not pass inspection for residential premises wiring. The manual may say that, but this seems to me to be in reference to ALLOWABLE engineering to close tolerances in an industrial setting, where approved electrical engineering analysis may run the currents to more precisely calculated limits... again, that is NOT ALLOWED for residential premises per NEC, so never put a 40amp circuit breaker on 10 gauge wire.

    "The National Electrical Code [NEC] requires their own cable sizing for premises wiring. Refer to the NEC rules to determine building wiring, as this page relates to electronic equipment wiring. For reference, the ampacity of copper wire at 300C for common wire sizes
    14 AWG may carry a maximum of 20 Amps in free air, or 15 Amps as part of a 3 conductor cable.
    12 AWG may carry a maximum of 25 Amps in free air, or 20 Amps as part of a 3 conductor cable.
    10 AWG may carry a maximum of 40 Amps in free air, or 30 Amps as part of a 3 conductor cable.
    8 AWG may carry a maximum of 70 Amps in free air, or 50 Amps as part of a 3 conductor cable."

    You should be fine on the dryer circuit, as it is (check the main to be sure) 30 amp on 10gauge wire.


    I just finished wiring my garage with a sub-panel and 8 circuits this week, in Phoenix AZ, and did calculations on all my tools including the length of the runs and the high temp in the attic, then took it all over and went over it with the city inspector. I ran 20 amp 12 ga 230V for my 3hp. Good luck!
    Last edited by Dave MacArthur; 06-03-2007 at 12:41 AM.

  6. #6
    Join Date
    May 2007
    Location
    Ventura, CA
    Posts
    530
    Thanks Gary, Tom & Andrew for your helpful replies. Sounds like this might be doable after all.

    Tom, I think Gary may have answered your question -- the continous load will be much lower than the peak load, so perhaps a smaller wire gage can be used under those circumstances.

    Most importantly, it sounds like at least two of you are running 5HP motors on circuits that are similar to what I have available. That info is worth its weight in gold to me right now.

    So thanks again This forum is wonderful place to learn.

    -Tom H.
    Ventura, CA

  7. #7
    Join Date
    May 2007
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    Ventura, CA
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    Dave-

    My goodness -- thanks for that! You have the gift for teaching....

    -Tom H.

  8. #8
    Join Date
    Jun 2005
    Location
    Trinity County California
    Posts
    729

    Running a 220v saw

    When my house was being constructed, I ordered my machinery and told my electrician to wire the shop accordingly. So I just didn't arrive at the electrical specs by cherry-picking from brochures..

    If I get some larger machinery, I may even pull in 3-phase power since out rates in this county are rock-bottom.

    Gary Curtis

  9. #9
    Join Date
    Mar 2003
    Location
    SE PA - Central Bucks County
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    65,688
    Quote Originally Posted by Gary Curtis View Post
    If I get some larger machinery, I may even pull in 3-phase power since out rates in this county are rock-bottom.
    Be sure you understand how they will bill you for the 3-phase...some folks have posted about "surprises" when they have one month with a lot of use and then their bill never subsides when they go back to not pulling much...a phase converter could be less expensive in the long run in those cases.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  10. #10
    Join Date
    Feb 2007
    Location
    Ames, IA
    Posts
    102
    You can use an 30 amp HACR type breaker which is a time delay breaker. Unlikely that you will need it though. Dave did a good job of covering the bases. 80% is the norm for continous use. Continous is defined as 3 hours or more. On motor circuits the wire should be sized at 125% of the full load amps (FLA) of the motor. At 16 - 20 amps, 10 guage will be the right size for your application.

    Gary,
    As for the 3-phase it is very unlikely that a utility company will allow 3 phase on a residential premises. Even for small commercial shop operations that wish to install you often have to justify to the utility company that they will get a return on their investment. Then they use a multipler to drive the cost up on the kwh price. I went through this while back with a client who had a cabinet shop after we installed 3-phase power to his shop. He found afterward that it wasn't 1/3 of the price to operate his machinery. In fact his bill went up considerably. He had previously been using phase converters to operate his 3-phase equipment. I am with Jim, stick with the converter unless you are a large production enviroment.

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