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Thread: RPC question

  1. #11
    Join Date
    Jan 2004
    Location
    Missouri
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    16,738

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    Quote Originally Posted by gearhead
    Very good information here. Right now I just have the one 3 phase machine. Can I just put on a female 3 phase plug on RPC 3 phase out end and then plug in the different machines as I get them.
    I see no reason why you could not do that.

    The machine needs a local motor starter with overload protection, but that would be the case even with a panel.

    To simplify everything, you can just leave the VFD on the DP... it functions as motor overload protection, and it offers some distinct operational advantages.

  2. #12
    Join Date
    Jul 2001
    Location
    Green Bay, WI
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    2,519

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    All my rotary phase convertors (RPC) have plugs on them

    I use a standard 240 V -30 amp plug for the inlet and a 240-20 Amp recepticle on the outlet of the RPC. this prevents plugging in a 3 phase motor into the single phase wall supply, as all outlets are 30 amp (twistlock).

    It also allows flipping RPCs for tests
    RPCs also are on small skids for easy moving with a hand truck

    Rich

  3. #13
    Join Date
    Jan 2006
    Location
    Kansas City Mo
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    142

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    A change in the program, I came across a guy who has a 30 circuit 3-phase panelboard at a just about give it way price. The circuit breakers will be $5.00 for each one I need. This project is really starting to come together.
    The panelboard is really much bigger than I would ever use, but its avail.

    J Tiers mention I would still need somekind of overload protection even with a panel. Don't the breakers work as the overload protection? I realize some of the questions are painfully stupid, but I'm new to the RPC world and I'm expanding my shop so I'll take all the advice I can get. gear
    Last edited by gearhead; 05-18-2009 at 04:05 PM.

  4. #14
    Join Date
    Jan 2006
    Location
    Kansas City Mo
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    142

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    Just about ready to pass on the panelboard it's 34 inches long, 21 wide and 5.3/4 deep. WAY to big for my needs...Back to the plug ins I guess...
    Last edited by gearhead; 05-18-2009 at 06:23 PM.

  5. #15
    Join Date
    May 2005
    Location
    Salisbury, MD
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    431

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    I took the output of my RPC to two banks of fuse holders. By output I mean after the balancing caps but inside the box that houses most everything.

    Each bank of fuse holders houses three 10 amp fuses, one for each leg of the output.

    I used 10-3 (with ground) solid copper from the output of each fuse bank to an outlet. One outlet is behind the mill the second behind the lathe. The plug/outlet acts as the disconnect.

    Also, in my small shop when I am standing at the lathe I can reach the breaker panel; so I could shut off the entire building if necessary.

    My RPC is "permanently" installed. The idler is on a shelf near the ceiling, out of the way. The panel box housing the caps is mounted near the shelf as is the motor controller.

    Don't know how "right" that is but it seems to work.

  6. #16
    Join Date
    Jul 2008
    Location
    San Diego
    Posts
    102

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    I have a 7.5 hp homebuilt RPC running a 3 hp mill and 3 hp lathe. The RPC output is a branch with three plug in outlets, no panel. I guess I need to buy another 3 ph machine...

    Jim

  7. #17
    Join Date
    Jun 2005
    Location
    Mapleton, IL
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    In answer to one of your recent questions....circuit breakers are not available (typically) in very small increments. They are used to protect the *wiring* from exceeding its rated values. Since there are very few wire sizes, with some pretty standard current carrying ratings, the breakers for standard panels are to match those circuit values.

    Motor protection, on the other hand, is usually accomplished either with fuses (in a fuse block, often in a fused disconnect) for each unit. A given circuit can theoretically serve more than one motor...which is another reason the circuit breakers in a panel are not used to protect the motor. You would then need to size the circuit (and circuit breaker and wire) to serve two motors. By the time one drew enough current to trip the breaker feeding both motors, the motor would be toast....but I digress

    The more common means of protecting motors today is with heater-based overload protection. Often this is an item that attaches directly to a magnetic motor starter (self-latching relay). The heaters heat some low-temp alloy that melts and allows a spring loaded mechanism to disconnect the load. The heaters are available in tiny increments so that you can properly protect any motor. The heaters are specific to a given vendor of the motor protector...and often to a given series of that protector. Charts show you which heaters to use with a given current load...for single, three phase, etc.

    When these heated protectors do their job, they are resettable by pushing a button that sort of rewinds the spring mechanism...which is then held back in its operating position by the low-temp alloy that has re-hardened.

    More than you wanted to know...but lots of folks never see this stuff so thought I ought to describe it so you will know what you are looking for.

    Paul
    Paul Carpenter
    Mapleton, IL

  8. #18
    Join Date
    Jan 2006
    Location
    Kansas City Mo
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    I'm talking all the advice and information available. Never to much information. I have had some really great individuals in this forum reach out to me regarding the fusing systems they use. I'm very new to the RPC way of doing things, but I'm learning with each new post. Thanks again for the info........Gearhead

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