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How do I know if its 1 or 3 phase?

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  • How do I know if its 1 or 3 phase?

    The local grain elevator will let me plug in to do some welding. I know they use 440 to run the augers, legs and belts. How will I know what Im plugging into? What happens if you plug a single phase machine into a 3 phase outlet? Am I correct that a 220 outlet may not be compatible with my machine?
    Who do you call when the lawmakers ignore the law?

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  • #2
    Typically 3 phase is not run to an outlet. It may be run to a Hubbell type connector or even to a wall mounted junction box. 3 phase will have 1 ground and 3 hot legs.: Beware it is common for 230 VAC 1 phase to have 1 ground, 1 neutral, and 2 hots. This allows for 230 VAC as well as 115 VAC from the same outlet.

    It is very likely you will ruin a 1 phase machine plugging it in to a 3 phase receptacle.

    It is possible to have a 230VAC outlet receptacle that is not compatible with the plug on your welder.

    The best way to tell what voltage you are working with is to measure it with an analog VOM (Simpson 260 or similar) or Digital multimeter (Fluke 189). These are upper end tools of the trade and a cheap VOM (volt ohm meter) from Radio Shack will work fine.

    If you are not familiar with how to measure and which legs to measure, then please get a knowledgeable plant electrician or other qualified person to help you. 30-60 amps of 208+ 3 phase power can kill you in a literal heartbeat. So can 1 phase 220 VAC.

    Be cautious, careful, and good luck.

    If you can talk to the plant electrician, he can probably help you get wired in quickly.

    If this type work is going to be a regular for you, then perhaps an engine drive unit may be the answer. Most all plants accept LP or Diesel powered units. Gasoline powered welders are not allowed in a lot of plant applications. This may be off subject, but just a thought for the future.

    Good Luck,

    HAWK

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    • #3
      Im going to be doing my own work on my own equipment, just using their electricity. I was looking for a clean level place to work on my semi trailers so I didnt have to make 200 feet of extension cord to work at the house. I may have to make an adapter to match the plugs.

      If the plug has only 3 legs(like a common dryer or stove plug etc.) it for sure is NOT 3 phase? I know some of the newer appliances are using 4 conductors on the plugs but all my stuff is 3 wire.
      Who do you call when the lawmakers ignore the law?

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      • #4
        As Hawk said if you are not sure than you should find an electrician to help you out. This is not a time to be guessing as you can ruin your equipment or even worse be killed. I know that all of us hate to pay someone to do anything because we take pride in being able to do it all. Hopefully you can find someone to show you in person & explain it while helping you hook it up.
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        • #5
          This made me think of something.

          I havea cord for my shp room that is run off of a 1 phase 220 breaker. I split one of the legs off to make 120 outlet on the box as well adn it works fine. Could you not just use two of the hot legs and then the common or ground and get a 220 single phase out of a 3 phase junction box?

          I'm no electrician, just know a few very basic things (like black on brass to save you a$$ on 110 wall sockets and such) But have very little understanding of the rest, so i just wanted to toss this out there too.

          Also, in my searched o learn what i needed to hook up my stuff i learned that the NEW code for homes and shops alike is to have 4 wires for a single phase 220 outlet... 2 hots, one common and one ground. So just because there's 4 wires on something (especially newly built structure) does not mean it's 3 phase
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          • #6
            Originally posted by Flyingpig View Post
            If the plug has only 3 legs(like a common dryer or stove plug etc.) it for sure is NOT 3 phase? I know some of the newer appliances are using 4 conductors on the plugs but all my stuff is 3 wire.
            A 3 phase connector will have 4 or 5 conductors and will look nothing like a normal dryer or stove plug.

            You should just really ask the operator of the elevator... they'll have a plant electrician or a maintenance guy who will know...
            Last edited by bretsk2500; 11-22-2008, 01:53 PM. Reason: spelling
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            • #7
              Originally posted by turboglenn View Post
              Could you not just use two of the hot legs and then the common or ground and get a 220 single phase out of a 3 phase junction box?
              maybe... it really depends on how the the grain elevator's power service is setup... if it's coming off the supply transformer @440V WYE, then you're going to use 1 hot leg and the neutral... if it's supplied @208V WYE, then you use 2 hot legs and the ground. If the elevator is set up with 3 phase delta, call an electrician, seriously.
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              • #8
                Originally posted by turboglenn View Post

                I havea cord for my shp room that is run off of a 1 phase 220 breaker. I split one of the legs off to make 120 outlet on the box as well adn it works fine.
                Is this a 4-wire 120/240v Outlet? = OK


                If this is a 3-wire 120v/240v Outlet this is a very bad idea
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                • #9
                  Originally posted by turboglenn View Post
                  ...Could you not just use two of the hot legs and then the common or ground and get a 220 single phase out of a 3 phase junction box?...
                  You DO NOT purposely use the ground as a current-carrying conductor, as you do with a "common," or "neutral." I repeat, the ground and common are NOT interchangeable!

                  Some three-phase receptacles are 5-wire. This will include a neutral, but you will need to verify what the hot-to-neutral voltage is in that particular three-phase system.

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                  • #10
                    If they're running motors, it's probably 3 phase. Most likely 3 hot legs and a ground. At my work we have 3 phase drops, and our Millermatics and Syncrowaves have the matching plug, but are only using 2 of the hot legs plus the ground. With a meter you would get full voltage across all the hots, and lesser voltage from hot to ground, or hot to neutral.
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                    • #11
                      ame thing I had at my last job. I am a whiz with Automotive electrical and anything to do with it but the most I will do with home/shop electricity is replace a Plug and flip a breaker LOL. Stuff can kill....easily. I had a friend who was a union electrician of many years working in a middle school and the one slightly careless day he had.....zap....no more friend. Be careful. Dave
                      Originally posted by bob_e95482 View Post
                      If they're running motors, it's probably 3 phase. Most likely 3 hot legs and a ground. At my work we have 3 phase drops, and our Millermatics and Syncrowaves have the matching plug, but are only using 2 of the hot legs plus the ground. With a meter you would get full voltage across all the hots, and lesser voltage from hot to ground, or hot to neutral.

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