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Sanity check- rotary phase converter hookup

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  • Sanity check- rotary phase converter hookup

    Finally got around to picking up a rotary phase converter for the Abene I’ve been rebuilding for an embarrassing number of years.

    The RPC is 10hp 240v and from North American Rotary. Randomly checked Ebay the other day and it was only 20 minutes away from me and used under 24 hours total. Not a gloat-worthy deal, but 20% off list isn’t bad for near-new.

    Panel says 50a FLA, motor says 27a @ 240v.

    Sanity Check:

    I’m in the middle of reorganizing the workshop, but longest possible electrical run would be 50’ from the breaker box.

    I figure 50a breaker, 6ga copper to the RPC panel and motor, 8ga to the machine. Spindle is 5hp and feed is 2hp.

    Am I in the ballpark? Seems 8ga to the RPC panel might squeak by?

    thx.

  • #2
    Forgot the pics... Is nicely built. And seemingly upside down?
    Attached Files

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    • #3
      Hm. Well, not gloat-worthy at all, as American Rotary just dropped their Ebay price 20% for the 10hp ones, so I saved ~$4. Was ~$850 yesterday, now $679 with free shipping.

      oh well.

      if you’re looking for one, seems now’s the time to buy.

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      • #4
        I've been using an American Rotary 7.5 hp for 10 years or so. Couldn't be happier. It's well made and on mine, at least, the idler and even the capacitors are US made.
        Southwest Utah

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        • #5
          Been casually watching 10hp RPC for years, so jumped at a low hour commercial one for 20% less than retail.

          disappointed I now paid full retail, but the guy did add in a relay to cut power if a feed leg is lost, so I suppose decent deal. Not going to come back to him saying it’s worth less due to price drop. Will see if he can get the warranty transferred though.

          In any event, seems I have a 50a breaker handy and roll of 6ga copper...

          Is it proper to tie neutral to ground in the RPC panel? Seems that way to me. Also feed a ground to the idler, which was seemingly omitted previously (in spite of plastic conduit).
          Attached Files

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          • #6
            As far as your single phase input 8ga on a 50 amp breaker sounds about right. I'm running my 10 HP American Rotary on a 30 amp breaker but I don't push it hard. Do NOT tie the neutral to ground. In fact normally you don't even have a neutral in play for 3 phase. As far as feed from the RPC to the machine 10 ga is acceptable.
            Mike
            Central Ohio, USA

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            • #7
              Well, that is specifically what concerns me.

              Idler has a ground which was seemingly not used.

              Panel box had a ground, which seemingly went back to the breaker since there were snipped wires.

              Idler running ungrounded leaves me unsettled, as otherwise I have two hot legs coming in, and nowhere to connect Neutral. Judging by what was snipped, there were only 2 hot legs and no neutral. Ground was 14ga.

              Would prefer not dying in a fire is all.

              edit: to clarify, I saw no evidence of more than 3 conductors coming into the 3phase panel. Only see 3wires to the idler, so hot, hot, neutral.

              seems to me this should all be grounded. I see no evidence of this being done, and now doubting “professional electrician”.


              Last edited by AWS; 05-15-2020, 12:09 AM.

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              • #8
                You only need a neutral if you will be running something on 120 VAC on one leg of the 240 VAC line. But you should always have a safety ground connected back to the service entrance and (possibly) also to a ground rod, water pipe, or steel building frame. It might be a good idea to connect a resistor of 50k or so from one of the 3 phase lines to ground to bleed off static voltage build-up if the supply is totally floating. But I don't know if those suggestions are approved by code, so verify that before putting your installation into service.
                http://pauleschoen.com/pix/PM08_P76_P54.png
                Paul , P S Technology, Inc. and MrTibbs
                USA Maryland 21030

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                • #9
                  Originally posted by AWS View Post
                  Well, that is specifically what concerns me.

                  Idler has a ground which was seemingly not used.

                  Panel box had a ground, which seemingly went back to the breaker since there were snipped wires.

                  Idler running ungrounded leaves me unsettled, as otherwise I have two hot legs coming in, and nowhere to connect Neutral. Judging by what was snipped, there were only 2 hot legs and no neutral. Ground was 14ga.

                  Would prefer not dying in a fire is all.

                  edit: to clarify, I saw no evidence of more than 3 conductors coming into the 3phase panel. Only see 3wires to the idler, so hot, hot, neutral.

                  seems to me this should all be grounded. I see no evidence of this being done, and now doubting “professional electrician”.

                  I installed a 5hp earlier this year. Four wires between the idler and rpc panel, one of them ground. Three wires from the breaker box to the rpc panel. I just followed the instructions that came with it. If you don't have them you can download them from their site,
                  Tom - Spotsylvania, VA

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                  • #10
                    Here is a picture of the wiring in my 5hp North American cabinet. As you can see, the ground from the idler (black), the 240v inlet (bare) and the outlet to the load (green) are all terminated at the grounding lug at the bottom of the cabinet. This is per the instructions that came with it.

                    P.S. I just realized that the wiring in the picture is not complete. The three wires from the idler and the three wires to the load all connect to the terminal block above the T1 T2 T3 label. If I recall the idler connects to the larger bottom lugs and the load to the upper lugs.

                    Click image for larger version  Name:	rpc.jpg Views:	0 Size:	159.9 KB ID:	1875115
                    Last edited by flathead4; 05-15-2020, 08:08 AM.
                    Tom - Spotsylvania, VA

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                    • #11
                      Ah. Somehow did not see the downloads section of their site, so missed the install document.

                      looks like they spec 6ga single phase, 30-50a breaker, 2 conductor plus ground, and 10ga on the 3 phase side, 3 conductor plus ground.

                      Thanks all!

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