Page 1 of 2 12 LastLast
Results 1 to 15 of 19

Thread: Is 20 amp outlet on 30 amp circuit legal?

  1. #1
    Join Date
    Oct 2006
    Location
    Minneapolis, MN
    Posts
    5,426

    Is 20 amp outlet on 30 amp circuit legal?

    I would like to install another 220 volt circuit for an air compressor. The air compressor needs a 20 amp plug at best. Can I put a 20 amp receptacle on a 30 amp circuit and be legal?

    The code folks would probably be concerned about the 5 or 6 feet of 20 amp cable from the compressor to the receptacle not being protected.

  2. #2
    Join Date
    Nov 2007
    Location
    Near Charlotte, NC
    Posts
    1,056
    I don't know anything about what's legal, but this sounds like a serious fire hazard. Why not just use a 30 amp receptacle with the same prong configuration as the plug you need? There should be something you can find somewhere.

  3. #3
    Join Date
    Jun 2006
    Location
    Independence, MO, USA.
    Posts
    2,472
    Are you talking 220v 20 amp, or 110v 20 amp coming off the 220v 30 amp?

    You could add a fused disconnect box between it (dropping the amps).

    I don't know (availabilty or legality), but would a ground fault outlet work? (thinking out loud here)

  4. #4
    Quote Originally Posted by Brian Elfert View Post
    I would like to install another 220 volt circuit for an air compressor. The air compressor needs a 20 amp plug at best. Can I put a 20 amp receptacle on a 30 amp circuit and be legal?

    The code folks would probably be concerned about the 5 or 6 feet of 20 amp cable from the compressor to the receptacle not being protected.

    I can't speak to the code, but the physics say you'll be fine. However, if you're going to run thick enough wire for 30A, and install a 30A breaker, why not just go ahead and put in the 30A receptacle? It's easy to change the plug on the other end, and the receptacle price difference is minimal.

    That's what I did in my (future) shop. I just put all 30A receptacles in everywhere and will change out plugs as necessary.

    I'm not sure what you mean about the cable "not being protected." Maybe you can explain that a little more?

    Ben

  5. #5
    Join Date
    Oct 2006
    Location
    Minneapolis, MN
    Posts
    5,426
    This is 220 volt. I don't want to do a 30 amp receptacle because I already have the 20 amp plug and receptacle besides 30 amp is way overkill for the compressor. I am still looking for a deal on a larger compressor so I might need the 30 amp someday. I suppose I can put in a 20 amp breaker for now, but I might already have a 30 amp breaker.

    Circuit breakers are to protect the wiring, not the item powered by the circuit. The cable rated for 20 amps from the receptacle to the compressor won't be protected because the breaker is 30 amps.

    I've thought about it a bit and this should be okay as it is done all the time for bathrooms and kitchens. Code requires 20 amp circuits there, but nothing plugged in ever has a cord rated for 20 amps.

  6. #6
    Join Date
    Feb 2003
    Location
    Lafayette, IN
    Posts
    4,563
    Quote Originally Posted by Brian Elfert View Post
    I've thought about it a bit and this should be okay as it is done all the time for bathrooms and kitchens. Code requires 20 amp circuits there, but nothing plugged in ever has a cord rated for 20 amps.
    Bingo. Circuit breakers are there to protect hard wiring--closed up in walls or conduit--nothing more. You can even run a bunch of 15A 120V receptacles on a 20A circuit (must be more than one on the circuit, and a duplex receptacle does count as 2).
    Jason

    "Don't get stuck on stupid." --Lt. Gen. Russel Honore


  7. #7
    The only thing you have to make sure is that your 15A or 20A receptacle has a PASSTHROUGH rating of 30A. Most 15A outlets from the BORGs have a 20A pass thru rating. You can still fry the receptacle if excessive current is flowing in the rest of the circuit.

    On 20A circuits, I prefer to only put 20A receptacles where I know I'll need them. I put 15A receptacles on the rest (properly rated) as a way to limit loading with a bunch of high-amp devices. One thing I'd recommend if yr gonna mix and match amperage on yr receptacles for a single circuit: label the inside of the faceplate of each receptacle so you don't forget the actual rating of the ckt.

  8. #8
    Join Date
    Nov 2007
    Location
    Fort Pierce, Florida
    Posts
    3,498
    The issue concerning the breaker protecting the wire, concerns the wire in the wall, not the equipment cord. The equipment cord should match or exceed the equipment requirements.

    If the wire in the wall matches the breaker, there is no problem with a lower amperage receptacle since that limits the equipment that can be plugged in. In your situation, you can always replace the receptacle with a higher rated one if your equipment needs change.

    That assumes that you do not put a 20 amp cord/plug/recepticle on a piece of equipment that is going to draw 30 amps. If you did that, then the cord and receptacle could burn out before the breaker trips.

  9. #9
    Join Date
    Feb 2003
    Location
    South Windsor, CT
    Posts
    3,304
    Back to the original question - per the NEC (210.21 is the section), you can only have 30-amp receptacles on a 30-amp circuit.

    You can certainly have a 20-amp breaker protecting #10 conductors and use 15 and 20 amp receptacles on the circuit (the 15 amp receptacles are OK providing it's a multi-outlet circuit).

  10. #10
    Join Date
    Mar 2003
    Location
    Monroe, MI
    Posts
    11,896
    As anecdotal evidence, a guy I knew wired his whole addition with 12ga wire and put in 20A breakers. But he used 15A receptacles and the building inspector made him change them all out. He actually had a choice IIRC, change out the breakers or change out the receptacles, but they had to match.


  11. #11
    Join Date
    Jan 2007
    Location
    New Hampshire
    Posts
    2,796
    Not to beat a dead horse, but for weeks I've been trying to remember the other reason for not daisy chaining electrical outlets and you've found it.

  12. #12
    Join Date
    Feb 2003
    Location
    Lafayette, IN
    Posts
    4,563
    Quote Originally Posted by Matt Meiser View Post
    As anecdotal evidence, a guy I knew wired his whole addition with 12ga wire and put in 20A breakers. But he used 15A receptacles and the building inspector made him change them all out. He actually had a choice IIRC, change out the breakers or change out the receptacles, but they had to match.
    Matt, that's an inspector who doesn't know the NEC, then, or your friend's locale has some additional code. It's been a while, but that debate got hashed out here until someone found the appropriate section of the NEC that said you can have 15A receps on a 20A circuit (breaker and #12 wire), as long as there is more than one. I'm with Anthony, though--I would definitely pigtail the receps, not daisy-chain them at that point.
    Jason

    "Don't get stuck on stupid." --Lt. Gen. Russel Honore


  13. #13
    Join Date
    Nov 2007
    Location
    Near Charlotte, NC
    Posts
    1,056
    OK, for you guys in the know - what I would be worried about is someone checking the circuit, seeing it was 30amps, and plugging in a 30amp machine into the 20amp receptacle. Doesn't the receptacle itself have some level of wiring that could be in danger here? Or is the thought that someone would have to be so dumb to do this, it's not a worry?

  14. #14
    Join Date
    Mar 2003
    Location
    Monroe, MI
    Posts
    11,896
    I hadn't seen that Jason. I wouldn't doubt either scenario--he was in the City of Ann Arbor which is like Michigan's Little California. Maybe he was just being punished for killing beautiful living trees to shelter humans.

    On the original question, why not just install the 30A receptacle and put a 30A plug on the compressor? Or make a 1' cord with 30A plug on one end and a 20A receptacle on the other if you need to be able to move it to a 20A receptacle easily? As stated above, the breaker is protecting the fixed wiring. If you think about that lamp with a 16 or 18ga cord on a 15A circuit, its no different.


  15. #15
    Join Date
    Feb 2003
    Location
    Lafayette, IN
    Posts
    4,563
    Quote Originally Posted by Peter Quadarella View Post
    OK, for you guys in the know - what I would be worried about is someone checking the circuit, seeing it was 30amps, and plugging in a 30amp machine into the 20amp receptacle. Doesn't the receptacle itself have some level of wiring that could be in danger here? Or is the thought that someone would have to be so dumb to do this, it's not a worry?
    Receptacles and plugs are different configurations for that very reason. A 30A plug will not fit into a 20A receptacle:

    http://www.frentzandsons.com/Hardwar...nfiguratio.htm
    Jason

    "Don't get stuck on stupid." --Lt. Gen. Russel Honore


Similar Threads

  1. Using 3-wire 220V dryer outlet for tablesaw
    By Tom Henderson2 in forum WorkShops
    Replies: 9
    Last Post: 05-13-2008, 7:51 PM
  2. Amperage for Circuit to Run 3250B
    By Jesse Bushman in forum Turner's Forum
    Replies: 10
    Last Post: 03-03-2008, 10:59 PM
  3. Running a 220V saw from a dryer outlet
    By Tom Henderson2 in forum General Woodworking and Power Tools
    Replies: 9
    Last Post: 06-03-2007, 12:13 PM
  4. 120v Off of 240v Circuit?
    By Russ Filtz in forum General Woodworking and Power Tools
    Replies: 29
    Last Post: 01-02-2007, 2:06 PM
  5. Is there such thing as a 240V branch circuit?
    By Tom Jones III in forum General Woodworking and Power Tools
    Replies: 5
    Last Post: 07-18-2006, 4:49 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •