My RPC...

Gonna see if I can post a PDF here...

Hmmm... okay, it doesn't like PDFs of any reasonable size. It does, however, allow ZIP files, so I zipped it (compressing it by a whole 2k).

For anyone that's interested, I made a schematic diagram of my RPC and it's control circuitry, along with a thorough explanation of how each segment works.

Download this one, unzip it (with your favorite unzipping utility) and open the PDF.

Giving ambiguous credit, yet where due- I used ideas from many different machines to make this system work, so aside from putting all the pieces in, testing 'em, and replacing some burnt wires on-the-way, the rest was just natural physics.

In their honor and respect, I hereby bow my head and place one knee on the ground, for not only those who developed the wonderful mathematics that describes how these things work, but also to those that posted to the forums, with their insight and unselfish assistance, and of course, to the railroad, elevator, radio, and military equipment designers from whose machinery which I ever took liberty of design ideas and concepts.

Please be careful when building one of these things, stay protected in connections, tools, testing, and operation. If you die doing it, make it worth giving your life for, but make the choice wisely, as you only get one chance. For all the lesser opportunities, carefully pass them by, and spend another day with your family and friends.

You never, ever, switch the protective ground. You seldom, ever, switch the neutral.

RPCs don't need a neutral as none of the three-phase utilization equipment expects, or requires a neutral.

It's good that you are taking the control transformer power from L1 and L2 and not from L1 and N or L2 and N.

Hmmm...

Thanks for noting that, Peter- Looking at my drawing, and comparing it to my unit... I never actually DID it that way- thanks for pointing that out.

On my machine, I brought it in from the wall plug (a big range plug), and went straight to the cabinet grounding bar and idler frame, also to my LOAD side receptacles (machines are all hooked to the RPC via 3-phase receptacles.)

I purposely used the control transformer to grant isolation and current limitation... also used, but not shown, are fuses in the control-voltage output, as I originally planned to make the start and stop buttons remoteable from the RPC cabinet, either by 110v control branch harness, or using 24v relays and low-voltage remote wiring. I never did make a remote.

I also purposely designed it without need for Neutral, to avoid neutral-return current complications. I believe that when I originally drew this, I was planning on bringing neutral THROUGH that contactor, and in the process of re-drawing, blindly put it as ground. I shall fire my engineering draftsman, simply because I cannot apply 30 lashes to myself with sufficient authority to draw blood.

A fun read Dave!

Re that 3Ph/neutral thing, twice now, I've wished I'd run a neutral with the conductors in my 3Ph shop circuit, this because of on-hand motor starters/relays with 120V coils, heck, just a mounted light. Of course that adds the complication of 5 prong plug/receptacles if the machine is not hard wired. In both cases, I needed motor reversing.

I'm ignorant of any codes that forbid a neutral in a 3Ph conduit run, maybe I'm just ignorant? Just in case that's true, I didn't do it so you Osha types don't need to raid my little home shop, please. In my shop, there is no O in Osha, just little VERY non-profit me, no one "occupational".

Bob

No code issue there...

No code issue about neutral conductors in a 3-phase conduit, Robert- what Peter's referring to, is the fact that I drew my input contactor and input circuit breaker with the GROUND wire going through the breaker and LINE contactor... before going to ground. They SHOULD go DIRECT to the chassis bonding... so that if the contactor drops out, or breaker trips, I'll still have safety grounding.

In reality, I DID it that way, but for some reason, I didn't indicate it as such on my drawing.

One thing to keep in mind with re. to neutrals on three-phase...

3-phase symmetry is not 'pure' here, it's synthesized, hence, the neutral-to-phase voltages wont be symmetrical, they may be close enough to work properly. Instead, I use the control transformer for running coils, etc., ... and if there's another need, I add a 240-120v transformer.