15 December, 2013

120v

Was thinking that I need a 120v outlet near my air compressor, which is on 240v. Since the circuit is right nearby, any chance of problems if I just use one of the "hots", neutral, and ground to add a nearby 120v outlet. After looking around, I learned — (My answer is based on your wording that implies you have a 4 wire outlet, with two hots, a white and a legal equipment grounding wire or method. ) I think the determining feature is if your compressor hard wired, or cord connected? If it is cord connected then wire size, breaker size and receptacle size should all match, and adding a 120v outlet would be unusual, but I think it would just qualify as extending a multiwre branch circuit. I can't think of a NEC section that would prohibit it, but if somebody could quote one I would certainly vote for them as best answer, it's a big book, little hard to read sometimes. I do think you would have to leave it on a 2 pole breaker, two pole breakers are "common trip" so if one leg is cut and goes to ground it will open the whole circuit. And a GFCI would probably be required depending on location. Back when I was an apprentice I was told you could not use one leg of a two pole breaker, but the recent requirement to use handle ties or multiple pole breakers on multiwire branch circuits seems to contradict that. And it is normal to install multiple receptacles on a branch circuit that the use of all at once would overload and trip the circuit. If it is hard wired, then you have to treat the circuit as a motor circuit, it becomes fixed in place, the wire size may not match the breaker size. (For motors you are required to use wire sized only 125%, and allowed breakers 250-400% under certain conditions, which means you may have #14 wire, and a 50 amp breaker. ) It would not longer provide legal overcurrent protection in case of overload on an added receptacle. Whole host of problems.


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3 Comments

  1. Florida Smith December 12, 2013 at 11:47 pm #
    If the breaker trip you will not be using either one. Good luck
  2. Randi December 12, 2013 at 11:51 pm #
    Yes, if anything shorted in the compressor it would not trip a breaker until after your garage burns down. Other than that, it will workThey do make 14/3 ext cords and I use splitters in my garage. Spend the few dollars and sleep better knowing you're safe. Been doing electrical for over 20 years
  3. Harpy Birdman December 12, 2013 at 11:55 pm #
    You would have to provide a neutral all the way to the panel. Since you would be going through all that work you should just do the job properly and run a whole new cct to that location. 12/2 from panel to your new outlet and put it under a new breaker.