Wiring three phase: Oxtools/BarZ approach

I think the real bonus for Tom is that, if he ever gets 3Ph from PG&E, his panels are all set up. Pull new 200A conductors from the disconnect (behind the meter) to the load center (shop) and Bob's your Uncle.

I also watched three Bar Z's tutorials on conduit bending (as recommended by Tom). What a joy.
I've bent a little conduit and watching a Pro explain a few things was a lot of fun.
 
I think the real bonus for Tom is that, if he ever gets 3Ph from PG&E, his panels are all set up. Pull new 200A conductors from the disconnect (behind the meter) to the load center (shop) and Bob's your Uncle.

I also watched three Bar Z's tutorials on conduit bending (as recommended by Tom). What a joy.
I've bent a little conduit and watching a Pro explain a few things was a lot of fun.
I’d also guess Tom has been around enough industrial settings to know enough not to het in trouble.

watching those conduit videos is on my list, if I can remember his channel name, as I intend to use metal conduit for my few 3 phase drops.
 
To answer the original question: it depends. Every wiring style has its trade-offs. I wired my shop single phase, and used VFDs for years. Now that I have a phase converter, I'm not about to rewire everything. I currently run a 3PH extension cord to my 3PH machines.

I'll be putting a small pony 3PH panel suitable for the smallest number of breakers I can find. The 3PH plugs will be different from the rest - probably I'll choose 40A Hubble in Orange, to differentiate from my plethora of other plug styles
 
Did this one for the kid back in 2014.

A load center really makes it easy to add more equipment as needed.

Also did this one:
 
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@Karl_T Yep, that’s my plan when I get to the three phase part of my shop build, extend my RPC from a simple 20HP idler to a dual 10+20 idler configured to run as 10, 20, or 30 HP worth of idler. I’m also going to interface the lights so that if they get turned off the RPC cuts out a minute or so later as long as there is no load on the generated leg. With an isolated motor I will otherwise forget to cut it and the compressor off.
 
To answer the original question: it depends. Every wiring style has its trade-offs. I wired my shop single phase, and used VFDs for years. Now that I have a phase converter, I'm not about to rewire everything. I currently run a 3PH extension cord to my 3PH machines.

I'll be putting a small pony 3PH panel suitable for the smallest number of breakers I can find. The 3PH plugs will be different from the rest - probably I'll choose 40A Hubble in Orange, to differentiate from my plethora of other plug styles
Siemens makes a panel which I am using that holds four three phase breakers.
 
That's all an RPC really does. The other two legs are just passed through from the single phase.

I guess in the end it is just a question of how many single phase (120/240) vs 3 phase breakers you use, since you don't want to pull single phase power off the generated leg with an RPC, but no reason not to (in fact it's better for load balancing) if you have utility line 3 phase.
I don't get that...
3 phase feeds are 120 degrees apart. If you just add the 3rd leg, existing 2 phase are 180 degrees apart.
As far as I know, 3 phase motors rely on the 120 degree phase difference between the feeds for starting the motors and getting good torque and efficiency. What am I missing?
 
I don't get that...
3 phase feeds are 120 degrees apart. If you just add the 3rd leg, existing 2 phase are 180 degrees apart.
As far as I know, 3 phase motors rely on the 120 degree phase difference between the feeds for starting the motors and getting good torque and efficiency. What am I missing?
What you are considering is where the neutral is referenced to. In standard three phase, the neutral is often considered to be the center of the triangle. So 120 degrees between legs relative to neutral. In high leg delta 3 phase (google it for pictures), the neutral is the center of one side of the triangle. So two legs are 180 and one is 90 from neutral, but it is still an equal lateral triangle, 240 volts between any two legs. 3 phase motors don’t use neutral, so they don’t care what neutral is referenced to. RPCs produce 3 leg delta (correction, high leg delta) which is why you measure line to line voltage but get funky results for line to neutral.

Three leg delta is also fairly common in industrial use. It delivers the classic 3 phase, plus 240v and 120v single phase. Otherwise you get 3 phase with 208V leg to leg and 120V leg to center of the triangle neutral. A 240V 3 phase center to neutral would give something odd like 138V. At least I think that’s right, I’m doing geometry in my head so my math is not guaranteed.
 
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@rabler

You remember that I've already admitted to being electrically (and electronically) challenged, so excuse me.

IIRC, a very long time ago, I learned that single phase service is actually 120° (not 180°). Is that correct?

It made sense (at the time) related to pulling 1Ph off of 3Ph service and also generating 3Ph using an RPC.
 
@rabler

You remember that I've already admitted to being electrically (and electronically) challenged, so excuse me.

IIRC, a very long time ago, I learned that single phase service is actually 120° (not 180°). Is that correct?

It made sense (at the time) related to pulling 1Ph off of 3Ph service and also generating 3Ph using an RPC.
It’s a vector problem. You really can’t define an angle without two phases, two different sine waves. You measure a voltage between 2 points.
voltage=Vrms*sqrt(2)*cos(angle+2*pi*f*t), where f = 60Hz for US power. Angle is the the angle at t=0, but what defines t=0? (who cares? no one) So unless you’re dealing with more than single phase, angle is arbitrary.

In a 3 phase center neutral configuration, you have angles of 0, 120, and 240 from neutral to the three legs. But running three phases plus a neutral is 4 wires on the power line. The power company doesn’t run a high voltage neutral. Less wire is easier. They use transformers between any two legs to pull off single phase. Those two legs are at 120 degrees relative to the third leg, but without the third leg that angle becames meaningless. (They actually try to rotate which two legs to balance the loads). This produces one sine wave (cos wave) but since t=0 is arbitrary it doesnt really have an angle. Your 3phase motor will run fine off this config.

Since the transformer isolates the low voltage side, Neutral is determined by where the ground rod is attached. In a pure three phase only system, you could ground one of the legs. (IIRC this is called a corner ground system). The vector triangle is the same shape, it just shifts where relative to the origin it is placed. As long as your triangle maintains that shape, your three phase motor runs fine. Rotation and translation of that triangle don’t impact the motor.

The big fallacy, common even among EE’s, is there is some magical definition of a zero voltage point called ground. That is typically choosen as the local electrical potential of the earth. But an experiment on my old campus in the early days of networking showed a difference of up to 90V between two such rods less than a mile apart, and don’t ask what it is if a lightning strike occurs nearby. This has some nasty implications for attempting to send low voltage Ethernet signals between remote buildings.
 
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