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  • Another Noob 240V Question or two --

    Hi, all --

    New owner of a Miller 211. I have 240V in my garage with a 5-20r receptacle (currently used for my air compressor). I believe it necessarily is single-phase.

    The 211 and my 25-ft extension cord have 6-50p plug ends and a 6-50r receptacle on the cord.

    Two questions:

    1. After a lot of web surfing, I've concluded I can simply make up a cable with a male 5-20p end and a female 6-50r end, and plug straight into the 240V wall socket.

    Is this correct, or is there a better way to do this?

    2. I need to double-check my panel, but I believe I have 20 amp breakers feeding the 240V wall socket.

    Can/should I replace/upgrade the 20 amp breakers to 30 amp breakers?

    EDIT: If I do upgrade to 30 amp breakers, do I need to also upgrade the 5-20r wall socket?

    Thanks for the help!
    Mark
    Last edited by mneblett; 04-17-2013, 09:36 AM.

  • #2
    You can make the cord and t should work okay. I wouldn't upgrade teh breaker until you know what wire size you have in the wall. Breaker is to protect the wire and should be appropriately sized for the wire, not the load.

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    • #3
      A 5-20R is for 120 Volt, 20 Amps. ???
      Miller stuff:
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      • #4
        Originally posted by USMCPOP View Post
        A 5-20R is for 120 Volt, 20 Amps. ???
        240V, 20A. My wall socket meters at 248V across the hots with a cheap Sears voltmeter.

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        • #5
          Sorry, but a 5-20 is a NEMA rated 125 volt 20 amp receptacle. A 6-20 is a 250 volt 20 amp. rated receptacle. If you have a 5-20R with 248 volts across it, you need to change it,
          JIM

          Owner Operator of JNT Mobile Welding & Repair LLC
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          • #6
            Originally posted by jpence38 View Post
            Sorry, but a 5-20 is a NEMA rated 125 volt 20 amp receptacle. A 6-20 is a 250 volt 20 amp. rated receptacle. If you have a 5-20R with 248 volts across it, you need to change it,
            I'll double-check -- it is likely a 6-20r -- I saw a pic of a 5-20r with the same slot pattern on the face and jumped to conclusions. The socket was installed by an older licensed electrician, and based on what I saw I believe he did it "by the book."
            Last edited by mneblett; 04-17-2013, 03:46 PM.

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            • #7
              There are a few things you need to take into consideration. First is the load other words how many amps. The second is the distance to the fuse panel, the longer the distance, the thicker the wire you're going to need.
              For example if your plug is only 10 feet from the panel you could probably get away with 10 gauge wire, but like in my shop it over 100 feet away so I used 8 gauge and I have no problems(going on 3 years now).

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              • #8
                Forgot, I am running my mm211 on a 30 amp 240volt breaker. Hope this helps

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                • #9
                  Thanks for the additional input.

                  The wall socket is ~8 feet from the sub-panel. (After killing power) I'm going to pull the 6-20R socket to see whether I can determine what gauge is between the panel and the socket.

                  Depending on what I find, I've decided to skip making up a 6-20p/6-50R extension cord, and instead will see whether there is large enough wire in the wall to let me install a 30A breaker and replace the 6-20R socket with a 6-50r socket (and add a label indicating the 30 amp limit if the wall wire won't support 50A).

                  I expect to be in the house for a long time (already been here 17 years), so I expect that if the wire size is limiting, I'll get around to upgrading it sometime. In the meantime, I don't expect to ever have anything that pulls as much as the welder, and 30A will take care of that.

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                  • #10
                    Originally posted by mneblett View Post
                    Thanks for the additional input.

                    The wall socket is ~8 feet from the sub-panel. (After killing power) I'm going to pull the 6-20R socket to see whether I can determine what gauge is between the panel and the socket.

                    Depending on what I find, I've decided to skip making up a 6-20p/6-50R extension cord, and instead will see whether there is large enough wire in the wall to let me install a 30A breaker and replace the 6-20R socket with a 6-50r socket (and add a label indicating the 30 amp limit if the wall wire won't support 50A).

                    I expect to be in the house for a long time (already been here 17 years), so I expect that if the wire size is limiting, I'll get around to upgrading it sometime. In the meantime, I don't expect to ever have anything that pulls as much as the welder, and 30A will take care of that.
                    Famous last words... If you are in the wiring and have the money might as well bump it up to a 50amp circuit. Who knows what you will get next. Then you will be set and won't have to do it again!
                    MillerMatic 251
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                    • #11
                      Why not just install an l6-30r, 30 amp plug? That's what I use for my gear.

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                      • #12
                        Originally posted by Cgotto6 View Post
                        Why not just install an l6-30r, 30 amp plug? That's what I use for my gear.
                        The MM211 comes with the MVP so changing out the plug to 30amp connector would make the system useless as well as voiding the warranty once you cut off the MVP connector on the power cord.
                        Ed Conley
                        http://www.screamingbroccoli.net/
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                        • #13
                          Originally posted by Broccoli1 View Post
                          Originally posted by Cgotto6 View Post
                          Why not just install an l6-30r, 30 amp plug? That's what I use for my gear.
                          The MM211 comes with the MVP so changing out the plug to 30amp connector would make the system useless as well as voiding the warranty once you cut off the MVP connector on the power cord.
                          I see. I have a 180 and have never seen the MVP plug. Sorry for the bad advise. Learn something new everyday.

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                          • #14
                            I remember the days when a 6-50r was just called a "welder plug". If you had a welder this is what you used. Life was simpler.
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                            • #15
                              Follow-up --

                              First, thanks to all for the helpful info!

                              Between what I found here, a lot of searching/education, and dredging up old memories from EE 101, I finally decided to stop trying to figure out "make do" alternatives, and just "do it right." I've installed a dedicated 50A circuit breaker in the garage sub-panel and a completely new/separate 6-50R wall socket less than a foot away from the panel.

                              Next stops: pick up a 75/25 cylinder, and prepare a "safe" area in the garage to ensure I don't burn the place down!

                              Mark

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