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  • #16
    Originally posted by Abaker
    Agree with lakeside about having a breaker between the meter and the RPC. Not a code expert, but that won't pass.

    I have a question about disconnects at the machines: Do mag starters with thermal overloads count as fused disconnects? What about VFDs with thermal overload protection?

    No.... the overload contactors are just for the motor(s) -the fused disconnect kills and limits all power to the machine.

    For example, your RPC may put out 60 amps. You wire 6awg to the various disconnects that can be fused as small as requried for each machine. No way shoud you wire a high power souce to a lower power machine wiithout the appropriate limiting device.


    VFD's require breakers or fusing also. Sure, they have electronic means to limit current, but by code you need to protect against VFD failure. The VFD manfs list the fuse or breaker size required.
    Last edited by lakeside53; 02-22-2012, 01:21 AM.

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    • #17
      Originally posted by lakeside53
      VFD's require breakers or fusing also. Sure, they have electronic means to limit current, but by code you need to protect against VFD failure. The VFD manfs list the fuse or breaker size requried.
      And, if you actually FOLLOW the recommendations, you will be buying some expensive "semiconductor type" fuses in some cases. Others spec a more reasonable fuse, but it isn't that unusual to find the fuses for some VFDs cost $25 each.

      The RPC arrangement shown is quite standard, so long as you protect the RPC with an appropriate starter and overload.

      For US readers, the NEC has a section covering RPCs, giving the required protective stuff.

      It's a bit more common to wire the RPC "to the side", i.e. using it to supply the 3rd wire, and running the others from the 'source" as opposed to going through the RPC protection.

      If you go to ARCO electric's site, or some of the other makers, you will see the various wiring options actually shown as drawings you can download.
      CNC machines only go through the motions.

      Ideas expressed may be mine, or from anyone else in the universe.
      Not responsible for clerical errors. Or those made by lay people either.
      Number formats and units may be chosen at random depending on what day it is.
      I reserve the right to use a number system with any integer base without prior notice.
      Generalizations are understood to be "often" true, but not true in every case.

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      • #18
        It should be a good idea to check all the various options. 5 VFDs at $125 each may be more economical than 1 PC with several sub panels, conduits, breakers, etc. Like someone said, the VFD use power only when in use, the RPC will use power whenever it's running.

        Another thing to look at is the programs we have that provide low cost 3 phase to homes in residential neighborhoods for use with electric cars.

        Dan
        At the end of the project, there is a profound difference between spare parts and left over parts.

        Location: SF East Bay.

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        • #19
          Links to the ARCo electric (Roto-Phase maker) information. Better than advice from armchair hobby electricians.

          Wiring drawing
          http://www.arco-electric.com/PDFs/Ro...am11112005.pdf


          Installation info, including protection required etc. While this applies to their products, you can use it as a general guide to a similar item that you build, or get elsewhere. if it is for the same size load motor, it will as a rule be reasonably similar in its load requirenments
          http://www.arco-electric.com/InstallationGuide.aspx


          A general FAQ page about RPCs
          http://www.arco-electric.com/FAQ.aspx


          Phase-A-matic RPC info, for another source.

          Application notes page
          http://www.phase-a-matic.com/RotaryApplicationNotes.htm

          Brochure with some wiring info
          http://www.phase-a-matic.com/PDF/RPL.pdf

          More P-A-M notes
          http://www.phase-a-matic.com/PDF/RTN.pdf
          CNC machines only go through the motions.

          Ideas expressed may be mine, or from anyone else in the universe.
          Not responsible for clerical errors. Or those made by lay people either.
          Number formats and units may be chosen at random depending on what day it is.
          I reserve the right to use a number system with any integer base without prior notice.
          Generalizations are understood to be "often" true, but not true in every case.

          Comment


          • #20
            Originally posted by J Tiers
            Links to the ARCo electric (Roto-Phase maker) information. Better than advice from armchair hobby electricians.

            Boy, you sure know how to take the fun out of it. Facts. Bah!



            Dan
            At the end of the project, there is a profound difference between spare parts and left over parts.

            Location: SF East Bay.

            Comment


            • #21
              Wandering slightly OT... Home-built rpcs usually ignore idler motor protection, but it's required by code and easy to implement.


              If someone tells me how to post a pdf to this site (without just jpg conversion)... I'll upload a better quality schematic.

              Here's the JPG version of a pony start RPC. The pony run time is adjusted by the time delay relay. One future "enhancement" would be to detect the idler shaft speed and inhibit the main contactor operation if the idler couldn't spin up for some reason (like bad belt or whatever). As it is designed, the motor starter overload will protect the motor in this case. Why "pony" - I didn't want the big surge that results with dropping a 15hp motor across the 240 - you may not have this issue and can use the "other" approach; a potential relay, start caps (large in my case) and control contactor. Cpf and Cbx capacitors are for power factor and balance. Use Fitch's method to determine values. The overload section on the motor starter needs access between it and the main contacts - not all starters make provision for this so choose one carefully, and verify you can connect heavy wire at that point (6awg in my case) for T1 and T2.


              As most "affordable" rpcs (including all home built) are not typically UL listed, to get Electrical Inspector sign-off in this area you have to apply for "Special Permission" - difficult at best. Phase Perfect devices are UL approved so no issues if installed as per their listing and the NEC. I don't see many rpc in permitted situations.

              Last edited by lakeside53; 02-23-2012, 02:38 AM.

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              • #22
                I am a one-man shop. I have varying numbers of 3-phase machines. I have one RPC whose output is simply wired via conduit to six 3-phase disconnect boxes each of which is fused appropriately for its machine (if any). If I ever turned on too many machines I'm sure the 3rd leg would sag badly and eventually pop the breaker that feeds the RPC. So I don't.

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