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Thread: Wiring For Compressor Help...

  1. #16
    Plus this is a plug in device. The code is for the installation of the wire and outlet which I assume were followed. If the compressor was hard wired to the power source it would be a different story.

    Plug that compressor in and fire it up.

  2. #17
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    Quote Originally Posted by Frank Pratt View Post
    Guys, please don't be saying stuff like '#12 will be just fine' unless you know for a fact that the NEC says that it's fine. This is an area of the electrical code that is far more complex than most realize. The ampacity of #12 wire depends on the temperature rating the insulation, number of wires in the conduit and the termination temperature rating of the breaker or device at the load end of the circuit. And a motor load is more complex than a standard receptacle or lighting circuit

    I'm not going to say yes or no on this, because I'm a Canadian electrician. The NEC & CEC are largely harmonized, but not completely & I don't have access to the NEC. I'm just posting this because inexperienced people tend to get fast & loose with code requirements that do need to be adhered to.

    Please don't take offence with my comments, because that is not my intent.

    Frank, you seem to be doing the same thing...stating something without facts to back it up. But I see where you are coming from.

    A fact is that 12 gauge wire in the US, protected by a 20 ampere breaker is code approved. The breaker protects the wire, and avoids potential overheating and fire issues. Matching the Protective circuit breaker to the wire size is code specified.

    If the air compressor were to draw an unsafe amount of current, which would lead to wire overheating and danger, the circuit breaker would trip. This would tell the OP that he had an issue that needed attention.

    Chances are extremely high that the OP will have no problem whatsoever running that compressor on a 20 ampere circuit.

    Remember the NEC has no control over what a user might connect to a supply circuit. But it does have control over how a given circuit is protected, in the event a user connects something to it that exceeds its safe capacity to supply.

    No need to overthink this. Plug the compressor in and use it. In the UNLIKELY event the compressor pulls more current than the circuit is designed to supply the circuit breaker will trip. if that happens (likely will not) disconnect the compressor and upgrade the circuit. Doubt you will need to though...
    Too much to do...Not enough time...life is too short!

  3. #18
    Please...I didn't mean to cause a ruckus. I was hoping to get away with the 20A circuit, however after reading the replies, it kind of confirmed my own doubts in using the 20A circuit, although I likely would work just fine. I'm very mindful that circuits can heat up and cause bad things to happen. Because of this, I've just finished running a 30A circuit, only so that I can rest easier that nothing will be going on behind the drywall in my shop.
    Thank you for all of your informed responses. It really helped, hearing the different arguments for and against. And it confirmed what I knew from the start...you guys know a lot more about electrical than I do! Thanks again.

  4. #19
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    Quote Originally Posted by Bill Space View Post
    Frank, you seem to be doing the same thing...stating something without facts to back it up. But I see where you are coming from.

    A fact is that 12 gauge wire in the US, protected by a 20 ampere breaker is code approved. The breaker protects the wire, and avoids potential overheating and fire issues. Matching the Protective circuit breaker to the wire size is code specified.

    If the air compressor were to draw an unsafe amount of current, which would lead to wire overheating and danger, the circuit breaker would trip. This would tell the OP that he had an issue that needed attention.

    Chances are extremely high that the OP will have no problem whatsoever running that compressor on a 20 ampere circuit.

    Remember the NEC has no control over what a user might connect to a supply circuit. But it does have control over how a given circuit is protected, in the event a user connects something to it that exceeds its safe capacity to supply.

    No need to overthink this. Plug the compressor in and use it. In the UNLIKELY event the compressor pulls more current than the circuit is designed to supply the circuit breaker will trip. if that happens (likely will not) disconnect the compressor and upgrade the circuit. Doubt you will need to though...
    Bill, as I said, I am not going to say yay or nay because I don't have the facts. I was just making the point that when it comes to electrical code requirements the only information that should be given or taken is that which comes from reliable, qualified sources. My comments were not directed toward anyone in particular, or even this particular thread. It was more of a general caution on unintentionally giving unqualified electrical advice on an internet forum.

    Derek, I apologize for derailing your thread.

  5. #20
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    Frank
    No need for an apology.
    In the US there are many, many, tragic instances every year for not adhering to, or not understanding, electrical needs. There is nothing wrong with making people think about what they are doing prior to doing it. It's when folks are given the correct info and then choose to not use it, that it is frustrating.
    The most correct answer is to always advise a person to pull a permit, but folks are just very reluctant to do that for some reason???
    Derek was good with the 12 awg at 240, but I think he made a prudent choice putting the 10awg on a 30 amp breaker. Now he has a bigger sized circuit for future applications, without a huge increase in investment.
    "The first thing you need to know, will likely be the last thing you learn." (Unknown)

  6. #21
    Or you can look at it the other way that he had a circuit that was fine for the application and he wasted money and effort doing something that was quite unnecessary.

    Like I said, I'm running a compressor that is nearly identical to his and it's on a 20amp circuit fed by 12 gauge wire. I didn't see any reason why he shouldn't have plugged the machine into the circuit and let it run. Worst thing that could have happened is the breaker would have shut the power down.

  7. #22
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    Leo
    Derek has two values that are in conflict with with each other.
    First, the manufacturer gives the spec of 16.2 amps.
    Second Derek stated a spec of 3.7HP. ( Manufacturers manual states 3.5HP. Kobalt also does not spec circuit size in the manual online.)
    These two values, would not have the same answer for circuit sizing.
    "The first thing you need to know, will likely be the last thing you learn." (Unknown)

  8. #23
    Mike, let me also give you this experience. I have a 2HP DC. The manufacturer told me that a 20A would work just fine. Now, probably 30 percent of the time, on start up, the breaker trips. It did that since it was new. I learned a trick to turn it on, then turn it off, the first time I use it for the day. Once the impeller is turning, I turn it on. In my situation, I have one 30A line for the saw and one 20A line for other things.
    Since I won't ever run the compressor while running the table saw, I figured why not just run the 30A circuit for the comp and avoid any issues and hassles and worries. I mean...why not.

  9. #24
    Quote Originally Posted by Mike Cutler View Post
    Leo
    Derek has two values that are in conflict with with each other.
    First, the manufacturer gives the spec of 16.2 amps.
    Second Derek stated a spec of 3.7HP. ( Manufacturers manual states 3.5HP. Kobalt also does not spec circuit size in the manual online.)
    These two values, would not have the same answer for circuit sizing.
    Could be an inefficient motor. Could be locked rotor current. 3.7A x 746W/A divided by 220v is about 12.5 amp. But that is at 100% efficiency. Figure 82% efficiency and you're at 15.3 amps. 77.5% efficiency would get you 16.2 amps. Plus there are power factors in induction motors that affect the current draw.

  10. #25
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    I have wired quite a few houses and I never had an inspector ask me what I was going to plug in to a wall outlet. They just don't care. It is not part of their responsibility. All the local codes I have ever inspected don't even mention stuff like that. The tool manufacturer is not going to publish an owner's manual that instructs the owner of the equipment to do something that will burn down their house. Since no inspector will ever come to the original poster's house to see what is plugged in to every outlet, being safe is all that matters. The manufacturer will tell you how to install it safely.
    Quote Originally Posted by Frank Pratt View Post
    Local codes will always trump the owner's manual, at least as far as minimum requirements go.

  11. #26
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    If the NEC requirements for wire and breaker sizing are followed, then the circuit will not get hot enough to cause any problems, no matter what you plug into it. That is why the NEC specified current limits and wire sizes in the first place. Furthermore, there is a certain level of safety margin built into the code requirements. The reason I know this is I have been in charge of a lab that did over-current failure testing for the automotive industry. I can guarantee you that a 12 gauge wire will sustain much more than a 20A current indefinitely, unless it is in a conduit or bundle with other wires that provide additional heat or thermal insulation. If the original poster plugs his compressor into the 20A outlet, the absolute worst that can happen is the breaker will open up. That is true even if it is a 50 horsepower screw compressor - or a dead short for that matter.

    Quote Originally Posted by Leo Graywacz View Post
    Could be an inefficient motor. Could be locked rotor current. 3.7A x 746W/A divided by 220v is about 12.5 amp. But that is at 100% efficiency. Figure 82% efficiency and you're at 15.3 amps. 77.5% efficiency would get you 16.2 amps. Plus there are power factors in induction motors that affect the current draw.

  12. #27
    Quote Originally Posted by Art Mann View Post
    If the NEC requirements for wire and breaker sizing are followed, then the circuit will not get hot enough to cause any problems, no matter what you plug into it. That is why the NEC specified current limits and wire sizes in the first place. Furthermore, there is a certain level of safety margin built into the code requirements. The reason I know this is I have been in charge of a lab that did over-current failure testing for the automotive industry. I can guarantee you that a 12 gauge wire will sustain much more than a 20A current indefinitely, unless it is in a conduit or bundle with other wires that provide additional heat or thermal insulation. If the original poster plugs his compressor into the 20A outlet, the absolute worst that can happen is the breaker will open up. That is true even if it is a 50 horsepower screw compressor - or a dead short for that matter.
    Agree. that's what I said in post #21

  13. #28
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    Unless it's a Federal Pacific panel....
    Comments made here are my own and, according to my children, do not reflect the opinions of any other person... anywhere, anytime.

  14. #29
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    The quote feature didn't work like I expected. I was referring to post #24 in which Mike Cutler talked about what looked like contradictory information. The truth is the differences he pointed out don't amount to anything at all.
    Quote Originally Posted by Leo Graywacz View Post
    Agree. that's what I said in post #21

  15. #30
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    Quote Originally Posted by Art Mann View Post
    The quote feature didn't work like I expected. I was referring to post #24 in which Mike Cutler talked about what looked like contradictory information. The truth is the differences he pointed out don't amount to anything at all.
    Art
    I will have to respectively disagree with you on that point.
    I firmly believe that Derek was fine with his original setup. What I was attempting to answer was why there could be differences in the answers received.
    If I were to refer to Article 430 of the NEC, I will get a different breaker and conductor value, than using the manufacturers rated amperage, as specified in Derek's owners manual.
    The difference is that Derek is plugging his compressor into a receptacle and not hard wiring it per the NEC. The NEC stops at the receptacle, as long as power is going out. Coming in is a different story. The NEC most assuredly covers generators.
    I have a 5HP air compressor on 30 amp breaker with, 10/2 AWG ,SOOW cord. It plugs into a receptacle on the wall. I haven't violated the NEC, but the manufacturers warranty was void the moment I plugged that compressor in to the receptacle. The manufacturer spec's that the compressor be hardwired per the NEC. I also plug a 5HP, 35lb, commercial washing machine into the same receptacle, swapping plugs of course, without ever having had an issue.
    The NEC exists to protect the integrity of the conductors. What a person plugs into a receptacle is up to using their own common sense.
    "The first thing you need to know, will likely be the last thing you learn." (Unknown)

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