I learned I have 3 phase "high leg" at my new location, and need help using it

Why not? 12 GA is larger than 14 GA.

Yeah but since this is my first 3 phase rewire I feel more comfortable confirming with those smarter than me. The same calculator said I could go as high as 40A for this which sounds like a lot to me on 12AWG. I think the short 50ft run is coming into play more than I would have thought.

Starting from scratch I had already priced out 10AWG but pulling a panel apart that had an emergency light right next to the machine I found the 4 conductor run. Its nearly in a perfect spot.

The panel is a "Square D" A pair of 3 phase breakers were unplugged and sitting in the bottom. One is a 20A and the other is a 30A. I quickly wondered if buying a lottery ticket should be purchased as this machine is hopefully going to fire up tomorrow about a month before I was expecting it.
 
WOW!!!!

Some calculator, it and the code book do not seem to agree on much. #12 wire with THWN/THHN insulation is good for 20 amps. Under continuous load situation (constant load of 4 hours or more)it is rated for 16 amps. Wire is good, of any size, for 80% if its full load rating when the load varies, such as a receptacle circuit. There are lots of other sizing requirements also so error on the generous side of things.

There is a little book out there for about $16 that is a short read on a lot of the basics of wiring. It is called
UGLY'S ELECTRICAL REFERENCES by Geo. V. Hart. Well worth the money, makes things easier to understand, solves problems, has the answers to everyday problems and fits in your tool box so is always there. It is not very thick, 3/8" or so , so it is not real intimidating!
 
Yeah but since this is my first 3 phase rewire I feel more comfortable confirming with those smarter than me. The same calculator said I could go as high as 40A for this which sounds like a lot to me on 12AWG. I think the short 50ft run is coming into play more than I would have thought.
Just get a clamp on ammeter, HF sells them, Lowes, Home Depot etc.

Connect the thing up and measure the current(s), I think you'll be surprised with how good the margins are with what you have now. This stuff is not really that complicated, the ammeter will give you confidence and save you money.

edit: Search the sites I mentioned for "clamp meter".
 
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Table 430.250 minimum circuit size for 5HP 230v motor is 15.2 amps. So the short run of 12AWG would be OK, assuming there are no other adjustment factors to wire size, such as more than 3 current carrying conductors in the conduit. I would probably use #10 in a new installation since the cost difference would be minimal and allow future upgrades of equipment.
If the breaker is only for short circuit protection of the circuit then he could use the 40 amp breaker. See Table 430.52.
Notes to Table 310.16 refer to section 240.4(D) which limits small conductor to the commonly required overcurrent protection. However, it also refers to Table 240.4(G) which then allows other sections of the code to adjust overcurrent protection based on use of the circuit. Motors are specifically listed in Table 240.4(G). That allows the higher ratings in Table 430.52. Too small of breaker may cause nuisance tripping on motor start-up.
As long as there is proper overload protection at the motor he should be OK with the circuit.
 
I will second the recommendation of "Ugly's", it's very useful.

You have to be careful with those online calculators, and be sure you understand what they are giving you. There is a big difference between what a wire will handle in free air (like an extension cord), and what it will handle packed into a conduit with a bunch of other wires.
 
Its just the four 12AWG wires in a 1/2 or 3/4" conduit. Nothing else is shared on this conduit. I am going to power it up as is just to test the machine and change to 10AWG when we tear the machine down for its upcoming mild refurb. I need to go through it before it gets serious service.
 
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