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Thread: breaker, receptacle, plug for 3 hp dust collector

  1. #16
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    Hi Art - can you translate? I’m frozen. It seems I have the one machine in existence that cannot be safely plugged in without catastrophic failure of some sort or another...

    In other words .... what would you have me do at this point? I read all these threads that go way above most of our heads, and I think in the end most just plug it in and hope for the best.
    Last edited by Bob Riefer; 01-01-2020 at 5:48 PM.
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  2. #17
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    Jim is correct. And there is NOTHING wrong with a 20 amp on a 30 amp circuit. Nothing at all. The breaker on the wall is there to protect the wiring and the house/shop from fire. NOT to protect a motor or an appliance if it happens to draw more current than it should. If this was the case, you would have to size every piece of equipment in your home to exactly what is on the wall as a breaker. If you limit what you can plug into the 20 amp outlet (on the 30 amp breaker) to what is 20 amps or under, you are totally within NEC. If you plug a 30 amp load with a 20 amp plug and 20 amp outlet together, you are looking for issues. Keep your load below the rating on the plugs/outlets and you are FINE
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  3. #18
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    Quote Originally Posted by John Lifer View Post
    Jim is correct. And there is NOTHING wrong with a 20 amp on a 30 amp circuit. Nothing at all. The breaker on the wall is there to protect the wiring and the house/shop from fire. NOT to protect a motor or an appliance if it happens to draw more current than it should. If this was the case, you would have to size every piece of equipment in your home to exactly what is on the wall as a breaker. If you limit what you can plug into the 20 amp outlet (on the 30 amp breaker) to what is 20 amps or under, you are totally within NEC. If you plug a 30 amp load with a 20 amp plug and 20 amp outlet together, you are looking for issues. Keep your load below the rating on the plugs/outlets and you are FINE
    This post is 100% wrong.

    NFPA 70 (2017) article 210.21(B)(1)reads as follows;

    (1) Single receptacle on a branch circuit. A single receptacle installed on an individual branch circuit shall have an ampere rating not less than that of the branch circuit.
    Last edited by John Lanciani; 01-02-2020 at 12:56 PM. Reason: clarity of what was wrong

  4. #19
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    Quote Originally Posted by Bob Riefer View Post
    Hi Art - can you translate? I’m frozen. It seems I have the one machine in existence that cannot be safely plugged in without catastrophic failure of some sort or another...

    In other words .... what would you have me do at this point? I read all these threads that go way above most of our heads, and I think in the end most just plug it in and hope for the best.
    Bob

    You're wrapping yourself around the axle here. Plug your machines in and enjoy them. All the theoretical's here are just that, theoretical.
    You have the correct sized breaker, the correct sized conductors, your receptacle does not exceed either breaker, or conductor ratings. it was installed by a license and inspected. That's a huge step forward over most of the questions like this that are asked here.
    Neither the 3 HP motor, or the remote, is going to challenge the electrical installation as you have detailed it.
    If it worries you to leave them plugged in when not in use, unplug them when not in use. Many,many, people do. Many also have "whole shop disconnects" to secure power to all the machines, and receptacles, when not in use.Leaving only lighting.
    Enjoy your shop. You're on good solid "ground".
    Last edited by Mike Cutler; 01-02-2020 at 10:01 AM.
    "The first thing you need to know, will likely be the last thing you learn." (Unknown)

  5. #20
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    Quote Originally Posted by Mike Cutler View Post
    Bob

    You're wrapping yourself around the axle here. Plug your machines in and enjoy them. All the theoretical's here are just that, theoretical.
    You have the correct sized breaker, the correct sized conductors, your receptacle does not exceed either breaker, or conductor ratings. it was installed by a license and inspected. That's a huge step forward over most of the questions like this that are asked here.
    Neither the 3 HP motor, or the remote, is going to challenge the electrical installation as you have detailed it.
    If it worries you to leave them plugged in when not in use, unplug them when not in use. Many,many, people do. Many also have "whole shop disconnects" to secure power to all the machines, and receptacles, when not in use.Leaving only lighting.
    Enjoy your shop. You're on good solid "ground".
    Happy New Year Mike.

    Maybe I missed something however I was under the impression that the OP has a 20 ampere receptacle on a 30 ampere circuit?

    Regards, Rod

  6. #21
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    Quote Originally Posted by John Lanciani View Post
    This is 100% wrong. NFPA 70 (2017) article 210.21(B)(1)reads as follows;
    (1) Single receptacle on a branch circuit. A single receptacle installed on an individual branch circuit shall have an ampere rating not less than that of the branch circuit.
    I think you have it backwards, my reading of that is don't wire a 15A socket (receptacle) in to a branch that's rated or supplied by a higher rated breaker, such as 20A or 30A.

  7. #22
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    Quote Originally Posted by ChrisA Edwards View Post
    I think you have it backwards, my reading of that is don't wire a 15A socket (receptacle) in to a branch that's rated or supplied by a 20A breaker.
    OP has a 20 amp receptacle on a 30 amp circuit. The receptacle has an ampere rating (20a) less than the branch circuit rating (30a) and thus is disallowed.

    The receptacle is part of the branch circuit and must be sized accordingly.
    Last edited by John Lanciani; 01-02-2020 at 12:39 PM.

  8. #23
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    Quote Originally Posted by John Lanciani View Post
    OP has a 20 amp receptacle on a 30 amp circuit. The receptacle has an ampere rating (20a) less than the branch circuit rating (30a) and thus is disallowed.

    The receptacle is part of the branch circuit and must be sized accordingly.
    I agree with you here, but my response was to your response where you quoted John Lifer and started out by stating "This is 100% wrong".

    Originally Posted by John LiferJim is correct. And there is NOTHING wrong with a 20 amp on a 30 amp circuit. Nothing at all. The breaker on the wall is there to protect the wiring and the house/shop from fire. NOT to protect a motor or an appliance if it happens to draw more current than it should. If this was the case, you would have to size every piece of equipment in your home to exactly what is on the wall as a breaker. If you limit what you can plug into the 20 amp outlet (on the 30 amp breaker) to what is 20 amps or under, you are totally within NEC. If you plug a 30 amp load with a 20 amp plug and 20 amp outlet together, you are looking for issues. Keep your load below the rating on the plugs/outlets and you are FINE





    This is 100% wrong. NFPA 70 (2017) article 210.21(B)(1)reads as follows;
    (1) Single receptacle on a branch circuit. A single receptacle installed on an individual branch circuit shall have an ampere rating not less than that of the branch circuit.
    All's good.

  9. #24
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    Quote Originally Posted by ChrisA Edwards View Post
    I agree with you here, but my response was to your response where you quoted John Lifer and started out by stating "This is 100% wrong".



    All's good.

    Gotcha. I was referring to the poster I quoted saying what he wrote was incorrect.

  10. #25
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    Quote Originally Posted by Bob Riefer View Post
    I talked to another electrician last night at a new years party. He thought that swapping out the breakers for 2-pole 20 amp breakers was the best bet at this time.

    His reasoning was that if both tools (previous to me owning them) were happily working with 20 amp plugs on 20 amp receptacles, then let's match the breaker to that setup. If the breakers start tripping, we'll quickly learn that upgrading to 30 amp breaker, receptacle, and plug are in order.
    I agree with this, for the reasons Art mentioned. FWIW, I had both a 3hp saw and dust collector on the same circuit for years without an issue. They're actually never starting at the same time anyway.

  11. #26
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    :-) Thanks everyone for helping me.

    Here's my final plan of attack:

    Step 1: I emailed Woodtek (maker of my dust collector) and asked a very clear/direct question... Given that 10 gauge wire has been run to a dedicated location for just this piece of equipment.... do you recommend 20 amp 2-pole breaker with 20 amp receptacle and 20 amp plug? or 30 amp 2-pole breaker with 30 amp recept and plug?

    Step 2: Sent same question to Grizzly (maker of my table saw).

    Step 2: Based on their replies, I'll do make any needed adjustments and be DONE! LOL
    - Bob R.
    Collegeville PA (30 minutes west of Philly)

  12. #27
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    The only problem I see with your installation is that a 30A circuit should always be paired with a 30A wall outlet. If it isn't, you introduce the possibility that someone will run 30A through the 20A receptacle and cause it to overheat. As long as you don't do that, you are fine (if not strictly code compliant). I have seen instances where somebody used a 3 for one adapter rated for 5 or 10 amps to power a 15 or 20 amp tool and the adapter melted. It is the same sort of problem that could happen here.

    I went through the explanation about motors with various faults because people need to know that a breaker is not designed to protect anything beyond the wall plug. If you stall a motor rated for say 16 full load amps, the motor will either be protected by its own internal thermal overload breaker or the motor will probably burn up regardless of the breaker size.

    Quote Originally Posted by Bob Riefer View Post
    Hi Art - can you translate? I’m frozen. It seems I have the one machine in existence that cannot be safely plugged in without catastrophic failure of some sort or another...

    In other words .... what would you have me do at this point? I read all these threads that go way above most of our heads, and I think in the end most just plug it in and hope for the best.

  13. #28
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    Quote Originally Posted by Rod Sheridan View Post
    Happy New Year Mike.

    Maybe I missed something however I was under the impression that the OP has a 20 ampere receptacle on a 30 ampere circuit?

    Regards, Rod
    Rod

    I believe that is correct.
    We do not know the total picture, What version of the code he was inspected to, or had to adhere to? Were there any exceptions?
    He had his installation done by a licensed electrician. It was inspected. He should be good to go.

    The discussion about having a 20 amp receptacle on a 30 amp breaker is somewhat academic. I'll agree to the single receptacle requirement, but there is not one thing wrong with having a receptacle installed on a circuit with a lower rating than the breaker. There are millions of them installed that way in the US. I installed hundred and hundreds of 120 vac, 15 amp duplex receptacles, on 20 amp breakers with 12/2 wire, while I was working toward my license in the 80's. Every one of them passed inspection.
    If you have a 240/30 amp breaker, and in some hypothetical scenario, the 240/20 amp load plugged into a 240/20 amp receptacle, on that 240/30 amp circuit, somehow sees more than 20 amps, but less than 30 amps, there is not one single difference electrically if it's plugged into a 30 amp receptacle, or a 20 amp receptacle at that point. I absolutely guarantee that a 240/20 amp duplex receptacle can take 30 amps for a given period of time. How it can be postulated for the theoretical value greater than 20amps but less than 30amps is a stretch. No breaker/receptacle combination is designed to protect against that fault scenario.
    The point about code compliance for a single receptacle on a branch circuit is valid, but that is all. For what ever reason though, he passed inspection. Let's all stop scaring the poor guy with hypothetical scenarios that are improbable, and let him enjoy his time and machines.
    Last edited by Mike Cutler; 01-03-2020 at 10:38 AM.
    "The first thing you need to know, will likely be the last thing you learn." (Unknown)

  14. #29
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    So, what you are saying is that a 20A wall plug is functionally identical to a 30A wall plug and that either should handle a 30A load on a regular basis. That is just ridiculous. Perhaps you are saying that everyone who uses a 20A wall outlet will verify that the load is not greater than 20A. That is also ridiculous. You seem to think that load currents in the range of 20 to 30 amps is unusual but in my observation, that is the norm in most advanced hobby and professional woodshops with 240VAC equipment. There is a reason why the National Electrical Code requires wall outlets to be sized according to the capacity of the breaker in the circuit. Someone has already referenced the applicable paragraph in this thread. The code was created under the assumption that people buy and sell homes and new owners may not be aware of any usage restrictions on existing wall outlets.

    You can guarantee that a 20A circuit will take 30A "for a given period of time" and I wouldn't disagree, but what we are talking about is continuous usage. Perhaps what you should do is rig up a 30A circuit and load it to 30A through a 20A outlet in a safe environment and see what happens. You will need minutes, not seconds, to see the outcome. Actually, with all your experience, I am surprised that you haven't already encountered melted plastic from overloaded outlets.

  15. #30
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    Art
    I respectfully disagree. The lugs in that 20 amp receptacle will take more than the current carrying capability of the conductors. Pass and Seymour, Crouse Hinds and Seimens will back that info up. The plastic insulator material is no different.
    And I have done some informal, and formal, destructive testing on breakers, and receptacles as part of receipt inspection for electrical components used in nuclear qualified environments. I used to test fuses up to 5000amps. I've blown up breakers, melted them in place, started fires with them. All in a lab. Sometimes for fun, just to see how much something would take, but generally not. I don't do it any longer.
    "So, what you are saying is that a 20A wall plug is functionally identical to a 30A wall plug and that either should handle a 30A load on a regular basis."

    No, what I am saying is that in this given instance, with the given variables involved, there is no electrical difference.


    The discussion wasn't centered around a load that was "expected" to be greater than 20 amps nominally, but some type of a failure/fault that would result in a condition greater than 240/20amps, but less than 240/30amps, with a 3HP motor. That is what I am referring to. If you know that your nominal amperage under load with no faults will be greater than 20 amps, then yes, there should be a 30 amp plug and receptacle. That isn't the case with this discussion.
    The original question was whether or not to plug in a remote DC starter, rated at 20 amps, into a 20 amp receptacle, on a 30 amp breaker protected circuit.

    Debate is always welcome and there is an opportunity for everyone to learn. In this instance though, the installation was installed by a licensed electrician. The work was inspected and signed off, and a 3HP motor under nominal loads, with no internal faults, is not going to challenge that breaker, the conductors, or the receptacle.

    I am not trying to be intentionally obtuse, or argumentetive.simply for arguments sake. I have been doing this type of work my entire working life,over 43 years.
    In that time I have never seen a receptacle catch fire, or melt, in and of itself. They are robust pieces of equipment. Faults in them, and switches, are usually traced back to poor initial installation, dirt dust, debris ,and grease, that gather inside, inferior materials, and oxidation.
    If you were to search back through all my posts dealing with shop electrical questions, I am conservative in my responses, and almost always advise a person to get a licensed electrician, and an inspection done. My personal belief is that most homeowners have no business going beyond resetting a breaker in the panel.
    The code exists for some pretty damn good reasons.It's not all about Seimens and Pass Seymour trying to gain market share through code requirement changes.
    Knowingly violating the NEC is stupid beyond reckless.
    Last edited by Mike Cutler; 01-03-2020 at 8:41 PM.
    "The first thing you need to know, will likely be the last thing you learn." (Unknown)

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