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Thread: 20amp machine on 30 amp circut?

  1. 20amp machine on 30 amp circut?

    I recently purchased a G0690- 220v 20A.
    I *may* purchase the G0634Z 220v 30A.
    My question is can both outlets be wired to a 30 amp breaker and just run one machine at a time? Will it damage a motor if you run it on a larger circuit than it is rated for?

    Also- im sure you can tell, I wont be doing the wiring for these machines but I would still like you know why or why not?

    Best Regards,
    Justin

  2. #2
    It wont have any effect on a smaller machine running on a larger circuit other than the fact that everything beyond the receptacle/junction box wont be protected by the breaker in an overload situation. That is to say if the motor were to short, the wiring and cord may likely burn before the breaker would trip. There was a recent, and long, discussion about this in the workshops forum that you may want to look into.

    Personally I dont see any problem with running two pieces of equipment, one 20A and one 30A, on a 30A feed. You can even run them at the same time if you choose, but it will only be for a second.

    Mark

  3. Thanks mark- ill try to find that thread.

    Best Regards,
    Justin

  4. Justin: I would consider pullng a second circuit off of your 30 amp outlet and installing a second outlet with a 20 amp GFCI circuit. Really the only reason to do this would be to protect the motor of your GO690 in an overload situation as stated.
    Bill

  5. #5
    Join Date
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    It has been preached around here until everyone should Get It! The circuit breaker protects the wiring to the outlet; NOT the machine.

    Each load must have it's own protection. This is what overload heaters in motor starters do. Also what fused disconnects are for. A Baldor motor service guy told me long ago, "Never depend on those "reset buttons" on motors. Add your own "real" protection." A commercial magnetic or manual motor starter with heaters sized for the motor is your first line of defense against motor burnout. A fused disconnect is overkill but there's nothing wrong with it! Each machine's cord and plug should be rated for it's amp load, or greater.

    Short version: It's bad to run a load too big for a given amperage circuit. 30A on a 20A circuit is a NoNo! But 20A on my 50A welding circuit; Okay!
    Happy Holidays!
    ~Chip~
    Necessisity is the Mother of Invention, But If it Ain't Broke don't Fix It !!

  6. #6

  7. #7
    Quote Originally Posted by William A. Parker View Post
    Justin: I would consider pullng a second circuit off of your 30 amp outlet and installing a second outlet with a 20 amp GFCI circuit. Really the only reason to do this would be to protect the motor of your GO690 in an overload situation as stated.
    Bill
    Not exactly the full story. The machine should be equipped with a thermal overload matched to the current draw of the motor- this trips out in the event of overload. The problem would be with the wiring. 30 amps needs 10 ga wire, and a 30 amp plug, 20 amps needs 12 ga wire and a 20 amp plug.

    Personally, I would just go ahead and install the right circuit for the machine, with the correct plug and wiring, etc. If you have the budget for the machines, you should try to squeeze out the few dollars more that it takes for a code compliant wiring setup.

  8. #8
    Quote Originally Posted by Stephen Cherry View Post
    Not exactly the full story. The machine should be equipped with a thermal overload matched to the current draw of the motor- this trips out in the event of overload. The problem would be with the wiring. 30 amps needs 10 ga wire, and a 30 amp plug, 20 amps needs 12 ga wire and a 20 amp plug.

    Personally, I would just go ahead and install the right circuit for the machine, with the correct plug and wiring, etc. If you have the budget for the machines, you should try to squeeze out the few dollars more that it takes for a code compliant wiring setup.
    There would be no reason, depending on the 30A circuit, that he couldn't do something similar to what William was suggesting. Simply installing a box with a 20A feed through breaker to pick up the 20A load at the end of the 30A circuit and protecting it *if he chose*. I personally think it would be foolish for all the reasons mentioned in the thread from the workshops forum that were repeated extensively. But if you really wanted to make sure the appliance was protected at 20 amps it would be a way to do it without causing a bunch more wire to be mined from the earth, plastic extruded around it, and all the other associated costs that go along with running a new feed.

    The only reason I bring this up is while we have a large shop perhaps unlike most with a basement or garage shop, running a new feed to a tool is not a "simple" or "cheap" task. When you consider the cost of a 150-200' wire run, breaker, conduit, and associated labor and misc. items its not "just run a separate circuit".

    If I have two machines in my shop, sitting side by side, that will never run simultaneously, and one is a 20A machine, and one is a 30-40A machine, you can be sure there will be one line run to that location. If I were super concerned, I could easily protect the smaller loads at the end of the circuit and save mining, refining, and manufacturing, a bunch of wire, and be just as safe.

    Mark

  9. #9
    Quote Originally Posted by Mark Bolton View Post
    There would be no reason, depending on the 30A circuit, that he couldn't do something similar to what William was suggesting. Simply installing a box with a 20A feed through breaker to pick up the 20A load at the end of the 30A circuit and protecting it *if he chose*. I personally think it would be foolish for all the reasons mentioned in the thread from the workshops forum that were repeated extensively. But if you really wanted to make sure the appliance was protected at 20 amps it would be a way to do it without causing a bunch more wire to be mined from the earth, plastic extruded around it, and all the other associated costs that go along with running a new feed.

    The only reason I bring this up is while we have a large shop perhaps unlike most with a basement or garage shop, running a new feed to a tool is not a "simple" or "cheap" task. When you consider the cost of a 150-200' wire run, breaker, conduit, and associated labor and misc. items its not "just run a separate circuit".

    If I have two machines in my shop, sitting side by side, that will never run simultaneously, and one is a 20A machine, and one is a 30-40A machine, you can be sure there will be one line run to that location. If I were super concerned, I could easily protect the smaller loads at the end of the circuit and save mining, refining, and manufacturing, a bunch of wire, and be just as safe.

    Mark
    Mark- you know that 99.99 percent of the time you are absolutely right, but the codes are written for when things go wrong. Most of the wiring practices, and corresponding codes, were written as a reaction to particular incidents. When I was an engineer, I would tell people starting out that the codes are all about fires and explosions, etc-- but they leave the gory details out and just tell you how not to catch on fire.

    The way to do what you describe, and I'm an not an electrician so there may be a little more to the story (electricians know exactly how to run wires), is to run the 30 amp line into another box with distribution, including a 20 amp breaker or fuses for the 20 amp circuit.

    Personally, I have seen too much stuff burned up, or blown up, due to cutting a few corners. For me the fundamental no-no is to run any conductor without a breaker or fuse providing adequate protection. The one thing to remember about electrical fires is that they start out hot- there is no smoldering for a few hours to set off the smoke alarm. All just my opinions though.

    Steve

  10. #10
    Join Date
    Jun 2005
    Location
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    729
    I've run a 19amp Baldor motor (table saw) on a 30 amp circuit for 5 years. The manufacturer, General of Canada, told me it would be OK, but not ideal. The poster who suggested running a sub-panel rated at 20 amps would be an improvement.

    Realistically speaking, why have a 30 amp circuit to begin with? Few machines draw that much at 220v, and it is illegal to have more than one 220v device operating at a time on a given 220 circuit. At least that is the code in California.

  11. #11
    Quote Originally Posted by Stephen Cherry View Post
    Mark- you know that 99.99 percent of the time you are absolutely right, but the codes are written for when things go wrong. Most of the wiring practices, and corresponding codes, were written as a reaction to particular incidents. When I was an engineer, I would tell people starting out that the codes are all about fires and explosions, etc-- but they leave the gory details out and just tell you how not to catch on fire.

    The way to do what you describe, and I'm an not an electrician so there may be a little more to the story (electricians know exactly how to run wires), is to run the 30 amp line into another box with distribution, including a 20 amp breaker or fuses for the 20 amp circuit.

    Personally, I have seen too much stuff burned up, or blown up, due to cutting a few corners. For me the fundamental no-no is to run any conductor without a breaker or fuse providing adequate protection. The one thing to remember about electrical fires is that they start out hot- there is no smoldering for a few hours to set off the smoke alarm. All just my opinions though.

    Steve
    I cant do anything but agree with you however, as has been stated, the 30A line "is" protected by code. This was gone over repeatedly in the workshops thread. The circuit is protected. We can choose to overprotect, or individually protect, every appliance in our home. A dedicated circuit protected by and individual breaker for every table lamp, TV, cordless phone, electric shaver, etc.. But we dont. We run a circuit that is protected and many many devices that draw far less than that circuit can provide are plugged in daily.

    Mark

  12. #12
    Join Date
    Apr 2007
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    1,417
    Sizing Wires and circuit breakers for 3HP and 5HP shop motor circuits


    3HP motor on 690 must use 17A from NEC tables for FLC. Continuous duty must be used, so you must multiply it by 125%, thus calculations must all be made with 21.25A. 12ga wire will flow 21.25A at 60C for wire termination critieria using NM (and of course 75C for connections to CB and motor itself will be met). 90C THHN wire or NM strands will carry the continuous duty FLC of 21.25A, so 12 AWG is fine. However, your circuit breaker should be sized above 21.25A, so 30A (I think that's the next standard up) should be used. 30A is fine on 12AWG wiring on a dedicated motor circuit as the "small conductors" rule is excepted for motors.

    If you're already going to run a 30A breaker, you should just use 10AWG and thus be set for both machines. Both machines protect the load/motor as well as the wires via internal overload thermal protection on the motor, the function of the breaker is to protect from ground fault or short circuit in this case. I think Stephen above mentioned you may not trust that overload protection, but in this case 30A CB will protect the circuit/wire perfectly anyways, and is very likely to work acceptably on startup surges.

    With a 30A circuit, you should use approved 30A receptacles and plugs. There is no reason you can't wire your 690 with a 30A plug, and considering the NEC mandates you plan for 21.25A on it, I think there's more reason to use the 30A plug than not. Certainly the intent of safe connections for expected amperage is met, and there is no downside--again, everything drives you to ensuring you don't run TOO SMALL in your wire and connections--larger is safer, particularly in that you're actually planning on protecting with the normal and expected 30A CB for the 10AWG already.

    The answer is "Yes", you can and should run both on a 10AWG circuit protected by a 30A breaker. Probably the most accurately acceptable thing you can do via the NEC. Absolutely nothing wrong with running larger size AWG than the load NORMALLY demands, most of the complexities of NEC motor calculations revolve around ensuring you DO have a larger conductor to act as a heat sink for the load and ensure temps stay low.
    Read my thread linked above for more details.
    Last edited by Dave MacArthur; 12-27-2010 at 3:33 AM.
    Thread on "How do I pickup/move XXX Saw?" http://www.sawmillcreek.org/showthread.php?p=597898

    Compilation of "Which Band Saw to buy?" threads http://www.sawmillcreek.org/showthre...028#post692028

  13. #13
    Do you run your 7 amp drill on a 15 amp circuit?
    Do you run your 3 amp sander on a 15 amp circuit?

    Your G0690 needs a minimum 20 amp circuit, not a maximum.

    Look at it this way. You can run multiple outlets on a circuit and run multiple tools at the same time provided the "total" current drawer doesn't exceed the line rating. Each tool doesn't drawer the max, and you don't need to run all tools at the same time to be safe.

  14. #14
    Quote Originally Posted by Dave MacArthur View Post
    Sizing Wires and circuit breakers for 3HP and 5HP shop motor circuits


    3HP motor on 690 must use 17A from NEC tables for FLC. Continuous duty must be used, so you must multiply it by 125%, thus calculations must all be made with 21.25A. 12ga wire will flow 21.25A at 60C for wire termination critieria using NM (and of course 75C for connections to CB and motor itself will be met). 90C THHN wire or NM strands will carry the continuous duty FLC of 21.25A, so 12 AWG is fine. However, your circuit breaker should be sized above 21.25A, so 30A (I think that's the next standard up) should be used. 30A is fine on 12AWG wiring on a dedicated motor circuit as the "small conductors" rule is excepted for motors.

    If you're already going to run a 30A breaker, you should just use 10AWG and thus be set for both machines. Both machines protect the load/motor as well as the wires via internal overload thermal protection on the motor, the function of the breaker is to protect from ground fault or short circuit in this case. I think Stephen above mentioned you may not trust that overload protection, but in this case 30A CB will protect the circuit/wire perfectly anyways, and is very likely to work acceptably on startup surges.

    With a 30A circuit, you should use approved 30A receptacles and plugs. There is no reason you can't wire your 690 with a 30A plug, and considering the NEC mandates you plan for 21.25A on it, I think there's more reason to use the 30A plug than not. Certainly the intent of safe connections for expected amperage is met, and there is no downside--again, everything drives you to ensuring you don't run TOO SMALL in your wire and connections--larger is safer, particularly in that you're actually planning on protecting with the normal and expected 30A CB for the 10AWG already.

    The answer is "Yes", you can and should run both on a 10AWG circuit protected by a 30A breaker. Probably the most accurately acceptable thing you can do via the NEC. Absolutely nothing wrong with running larger size AWG than the load NORMALLY demands, most of the complexities of NEC motor calculations revolve around ensuring you DO have a larger conductor to act as a heat sink for the load and ensure temps stay low.
    Read my thread linked above for more details.
    Dave, you may be absolutely right. I took a look at the Griz manual (definitely not a griz basher), and it looks like this machine is 12 amps full draw, and I think 14 gauge wiring (the wire to the motor is 14 ga). As I said earlier, I'm an engineer, not an electrician, but I've seen lots of stuff burned up due to cutting corners. The thought of 14 ga wire hooked to a 30 amp plug and breaker makes me cringe. Personally, I never wanted to be the one that everyone was looking at when something went wrong.

    How do you put a 30 amp plug on 14 awg power cord and meet code? Is it because it is a device, and not installed wiring?

    Personally, if I was doing something like plugging a 14 ga wire into a 30 amp circuit, I would get a breaker in a little box
    http://www.factorymation.com/s.nl/it...category=15748

    I'd have a 30amp plug with 10 gauge wire led to the breaker, and the supplied power cord on the way out.

  15. #15
    Join Date
    Dec 2006
    Location
    Toronto Ontario
    Posts
    6,468
    Whether you can run a machine on a given circuit includes one more variable that is machine dependant.

    The manufacturer may specify a maximum overcurrent rating which must be adhered to, regardless of what the NEC says.

    My Hammer machine, 240V 4HP is limited by the manufacturer to use branch circuit protection not to exceed 20 amperes.

    If the machine, or the manual is marked to indicate a maximum overcurrent value, you have to follow it.

    I couldn't use my machine on a 30 ampere circuit.

    Regards, Rod

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