Wiring a three phase circuit

[Frank Keeney]

I am hoping someone can give me some advice on running a 3 phase circuit. Basically, I have 5 machines that need electrical supply. I have a 20Hp RPC powered by single phase 200A load center with 100amp double pole breaker pushing out three phase from the converter panel into a 100amp disconnect. From the bottom lugs of that disconnect I was hoping that I could run #6 wire to the first machine contactor then somehow carry on that supply to the next machine's contactor without the need to buy a three phase panel and breakers($$$$). I was also hoping that I could run a second "circuit" to essentially daisy chain to the other three machines.

1st supply line: disconnect to Table saw 5hp to Planer 9hp,
2nd supply line: disconnect to Shaper 7.5hp to Radial Arm Saw 5hp to Jointer 3hp
With both of these originating at the bottom lugs of the disconnect

Only one machine will ever be powered on at a time. I assumed that the contactors, with their voltage overload protection, would allow it to be done. I don't know if this setup would require some sort of junction box to be able to "y" off to each machine at that point or if the power would be run from contactor to contactor? Please advise lol
Thanks in advance
Frank

[Phillip Mitchell]

I am not an electrician, but have done plenty of wiring including 3 phase, so grain of salt, etc...I'm sure some more qualified than me in electrical work will chime in.

Why would you not just get a reasonably priced MLO interior sub panel (used ones often have existing breakers already in them) and have proper circuits with receptacles? Breakers and receptacles and plugs exist for a reason. We are talking about a few hundred dollars for used equipment and not that much more for all new materials.

What you're describing sounds kooky.

[Frank Keeney]

The machines were previously hard wired and I assume they probably had dedicated electrical supply lines. I have found mixed information about how it can be accomplished otherwise, the main basis is cost. Adding a panel, breakers, plugs, outlets, outlet boxes, more wire, etc. It may be that in the end I am forced to do it that way, before I do I just wanted to see other opinions of it before I make a mistake lol

[Jason Roehl]

If you’re using contactors for each machine (I’m assuming a contactor on each machine), the way to “daisy chain” supply to each machine is to have some really large wire nuts on the hot (line) side of the contactor. Each of the 3 phases comes into the box containing the contactor and into a wire nut. From that nut, there would be two more wires—one to the contactor, and one to the next machine. You just need to go to an electrical supply house and get wire nuts that are rated for at least 3 #6 wires. I believe they’ll be blue.

[Frank Keeney]

I was told that with the rotary phase converter to never put the L3 or manufactured leg on L1 or L2, would this be an issue?

[John Pendery]

Like Phillip, I’m not an electrician, but have done my share of it. I think the only mistake you are in danger of making is foregoing a three phase panel with properly sized breakers/circuits between your rotary phase converter and your three phase machines. What you are describing sounds like a way to potentially damage machines and possibly your RPC. I would bite the bullet and purchase a small three phase load center and a couple properly sized breakers. All of my three phase machines have dedicated home run circuits back to the panel, but you might be able to get away with a couple of branch circuits, although I don’t feel comfortable giving wiring advice not knowing code and such in your area. I think trying to skimp on this stuff will come back to cause problems significantly more expensive than doing this correctly up front. A small three phase load center, breakers, and wire/conduit shouldn’t be too expensive. Good luck!

[John Pendery]

I was told that with the rotary phase converter to never put the L3 or manufactured leg on L1 or L2, would this be an issue?

You need to keep the manufactured/high leg off of sensitive electronics/controls. Check with a multimeter when getting your machines up and running.

[Frank Keeney]

This is just for hobby use and in my area it does not require code or inspection. I want to do it safely but also as cheap as I can. It seemed to me, in my most basic understanding, that due to the fact that only one motor would ever be running at once and the contactors having voltage overload protection at each machine that there would be a safe way to run the branches. I’m still undecided as to the pitfalls of doing what Jason has suggested with the wire nuts. What is wrong with that approach in my situation?

[Brian Holcombe]

Wiring it properly and by NEC code helps to avoid the potential disaster caused by unknown unknowns, the things you don't know that you don't know can certainly crop up and cause you a whole heck of a lot of grief, often more than the couple hundred or couple thousand saved.

[John Pendery]

Frank, I’m not sure other than knowing it wouldn’t work in my situation, and it sounds like an unusual approach to me. Hopefully some more folks will add to the discussion. I definitely understand where you are coming from though. Have you tried reaching out to the manufacturer of your rotary phase converter? They might be able to offer more specific guidance to the equipment you are working with.

[John Pendery]

Wiring it properly and by NEC code helps to avoid the potential disaster caused by unknown unknowns, the things you don't know that you don't know can certainly crop up and cause you a whole heck of a lot of grief, often more than the couple hundred or couple thousand saved.

Well said.

[Jim Becker]

Firstly, following the NEC/code is not something to avoid...not only for your own physical safety but to insure that if there is ever an issue and a loss, you'll not get hit with negligence and a "yuge" financial liability. Brian's comments are spot on.

"Daisy chaining" is not really a good practice in almost any application like this, especially with larger conductors. While my general machine circuit is not 3 phase, it does support multiple machines on the same circuit. All branching is done in two very large J-boxes where there is the room to work with the conductors with plenty of air space. A single run from there goes to each machine location and services a single machine termination. I would personally never "daisy chain" machines. I don't do that with any 240v receptacles. Do note that if you are going to do a shared circuit you need to size things for your largest load.

[Paul F Franklin]

Also not an electrician... The overloads in the motor starters protect the motors, but not the wiring. The overloads do nothing for you if you get a short in a junction box due to vibration or whatever. You need overcurrent protection for the wires. If the RPC disconnect has fuses or breakers that will do it, but the #6 wire isn't big enough to use with 100 amp fuse or breaker. If you run the feed from the RPC to a 3 phase panel, then the individual circuits can use smaller breakers and wires. You can still split a circuit to multiple motors as long as the wire is sized properly and the overcurrent protection is sized to protect the wire.

BTW, You can't put multiple large (like your #6) wires into a single lug in the disconnect. You would have to use a split bolt or polaris connector to split the feeds and the wire gauge from the disconnect to the split bolt or polaris need to be correct based on the overcurrent protection in the disconnect.

[Paul F Franklin]

Also, if the RPC has 60 amp fuses or breaker, or can be changed to 60 amp, you can use #6. Still need to use split bolts or polaris connectors to split the feeds.

[Frank Keeney]

I definitely plan on getting advice from the guy who manufactured the converter panel. The wire going from my 200amp single phase load center 100amp double pole breaker is two #2 conductors into the two single phase lugs of the converter panel then its #6 from the panel to the motor and from the converter to the fused disconnect. I respect electrical/electrical code and its not that I don't see the reasons for it being in place, but normally with these types of machines they are in a factory and being operated most of the time while other machines are also powered on. This made me think that maybe it could be done differently if only one machine is on at a time. I think some of the machines have a junction box already mounted on the machine in addition to the contactor/starter.

I did do some research on three phase sub panels, I wasn't sure about the recommendation for a "MLO" or main lug only and what that meant exactly. I assumed if I needed to get a sub panel (indoor) that I wouldn't need that many spaces. I think for the amperage of my largest machine I could likely get away with #10 at that point. Voltage drop doesn't seem to be an issue because no individual run would exceed about 35ft from the panel.

The split bolt or polaris connector to split the feeds is something I will definitely check out. I am open to any and all suggestions and advice.

Thank you all for your help!