Three Phase Wiring Questions

[George Bregar]

I am pretty much done converting my shop to vintage machinery of which almost all is three phase. I will be running a 20HP RPC, with the three phase output feeding a load center. I wired the existing shop...installed the meter pedestal, load center, branch circuits, etc. I will be doing this work also.

I will be running THWN/THHN in surface mounted EMT.


Questions I have that I would like confirmed:

1. Are conduit fill rules the same for 3 phase?
2. Are ampacity ratings the same also?
3. Black red blue wire with 3 phase?

My machines:

Machine	HP	Amps @ 220V
Oliver 88-DX	5	13
Woods Jointer	7.5	21
Oliver 399 Planer	3	8.6
Greenlee Mortiser	1.5	4.2
Fay & Egan 345	5	14.2
State OSS	1/2	2.2
Delta 12' Disc Sander	?	?
Blount Lathe	2	?

So just the Woods jointer needs #10 AWG, the rest 12. I was thinking of running the the bigger machines (jointer, Oliver 88, and F&E 345) off a 30A circuit, and the rest off a 20A circuit. My 3 phase load center is 125A and has four curcuits, so I will have some expansion if needed.

Thanks1

[Julie Moriarty]

1. Yes
2. Yes
3. Three phase 208v uses Black, Red, Blue for A, B & C phase. Around here for 480v we use Brown, Orange & Yellow for A, B & C. Of course, on 3 Ph motors, you need to get the rotation right too. The colors are used for identification should you need to trace out some problems. I've seen the three hots in a three phase installation that have no color identification. It works, you just don't have the color IDs to make troubleshooting easier. We use the different color schemes so the next person coming along knows if they are working on 208v or 480v. Just an extra added precaution.

General rules of thumb: Figure the load on your breakers at 80% of the stated amperage and match the wire size to the breaker size - #12 AWG for 20A, #10 AWG for 30A. Amperage ratings for wire are affected by the kind of insulation they have and the means by which they are installed. Wire in conduit will have a lower ampacity rating than wires in free air.

[David Kumm]

George, seeing your stuff I would oversize the conduit. I can see you going farther down the old iron spiral. My shop configuration made it easier to run a #8 line all around and then branch off to fusible disconnects at the machines and fuse accordingly. ( More for ease of wiring the plugs and disconnects are cheap on ebay ) Mainly because the air compressor is at the end and sometimes needs to run with the machines. The DC is on a vfd on a separate circuit but the main handles most of the machines. Dave

[George Bregar]

Thanks Julie.

David, so you oversize the circuit to 50A and then use fusible disconnects for each machine for over current protection?

[David Kumm]

Thanks Julie.

David, so you oversize the circuit to 50A and then use fusible disconnects for each machine for over current protection?

George, I oversize the circuit to 40 amps as my Phase perfect runs 30 amps with an overload for startup so a 40 amp breaker won't blow when I start the biggest motor. My 299 planer and compressor together need the #8 if on at the same time. The motor starter provides the machine protection , not the breaker, that is for the wiring. I just prefer to run smaller wire to the L15 plugs I use to make wiring easier and allow me to move machines if I change where they sit. I used to run both 20 and 30 amp twist lock but found it was easier to just use L15 for everything. The fusible disconnects would be redundant with the plugs but I'd need to run #8 right to the machine and hard wire. My shop is a five car garage with a center wall so running multiple circuits is a pain for a one man deal. Doesn't have a nice floor like yours. Dave

[George Bregar]

My DC, compressor, and heater are all single phase, and on their own circuit. So I don't have any potential for "surprise" loads. I can't imagine loads larger than the 7.5 HP motor on the jointer, so 30A should suffice. Most of my stuff can be 20A. I think I will just put the TS, jointer, and planer on the 30A circuit, and the rest on 20A circuit, to keep wire costs down. If i need additional in the future I have two add'l spaces, and I will go larger EMT so I can add wiring if need be.

[George Bregar]

So will a 30A circuit using 10 THHN be good? The run is less that 50'

[Jerome Stanek]

if a motor runs backward you just switch any 2 wires.

[Jeff Duncan]

Match your wire gauge up to your motors amp requirements, and your fuses off your wiring. So #12 wire uses a 20 amp fuse, #10 wire uses a 30 amp fuse. The thing to remember is the fuses are there to protect your wiring, not your machinery. Using oversized fuses does not provide the protection required. In other words, using a 30 amp fuse on your 12 gauge wire is not protecting the wire as it's supposed to be

I don't like to try to overfill conduits as it's generally easier to run another conduit closer to where the machine sits, than to try and get max fill on a conduit…..especially if you have a couple bends in there. Now of course if you have a long run between the panel and several machines then it does make sense to run a single larger conduit and split them closer to machines.

I use both disconnects and plugs w/ receptacles myself, though prefer plugs on smaller equipment as it's less expensive than fusible disconnects. I don't know what it states in the code, but the bigger you go the more likely you'll need the disconnects. In my shop I have disconnects on my dust collector (7-1/2 hp), shaper (7-1/2 hp), bandsaw (only 2hp, but it came with the disconnect so….), and CNC drill. Most of the smaller machines I have plugs on.

good luck,
JeffD

[George Bregar]

Jeff, thanks, but I think saying "Match your wire gauge up to your motors amp requirements" is not really accurate. I believe there are rules for sizing circuits for motor loads...I think it's 80% of the circuit size needs to handle the full load of the motor. So a 30A cirruit is required for 24 amps.

All my three phase machines, listed in my first post, fall into the category of "one at a time". There will never be a time when I have multiple machines in use. My dust collector, shop heater, compressor, are single phase loads. So no surprises. Although I was going to run multiple circuits until I saw the cost of three phse breakers....!

So my plan is to do what David suggested above...just run a single circuit for all my machines. I have a 20HP RPC. My largest load is my 7.5HP 16" Woods jointer. Is a 30A 10AWG circuit prper?

[David Kumm]

George, what is the output of the RPC? 10 sounds fine to me but as I said before my preference is #8 as I can get over 30 amps from either my Kay or Phase Perfect. Even though I can only use one machine at a time I like the wiring to carry my maximum output. THHN will carry 35 amps in conduit I believe. Others correct me. I've also had good luck with NOS three phase panels and breakers on ebay. Dave

[George Bregar]

Not sure, but what I really need to know is if a 30A three phase circuit using 10AWG is correct for a 7.5 HP 220V 21A motor. That's my largest load.

[George Bregar]

Nobody? I remember when an electrical thread couldn't NOT go at three pages.

[Duane Meadows]

George, 10AWG should be fine.

[Jeff Duncan]

Jeff, thanks, but I think saying "Match your wire gauge up to your motors amp requirements" is not really accurate. I believe there are rules for sizing circuits for motor loads...I think it's 80% of the circuit size needs to handle the full load of the motor. So a 30A cirruit is required for 24 amps.

George, maybe my phrasing wasn't as clear as it should be, but if you have a motor thats 24 amps, you'll find you need to go to a #10 wire, which dictates a 30 amp circuit. Now if you want to work the other way and say you need a 30 amp circuit which works with #10 wire, that's fine as well. It's the same point in that you need to use the correct sized wire for the size circuit being used, and they should be sized to your motors amperage requirements. My reason for bringing it up this way is b/c I think sometimes guys get confused and think the circuit breaker is there to protect the machine, and don't get that wire/breaker needs to be matched.

So yes, a 30 amp circuit w/ 10 gauge wire is just fine for your 7-1/2 hp motor. Your 5 hp on the other hand would run fine on a 20 amp circuit. Generally speaking having more capacity than you need isn't a problem except that it cost you more to run it. It's when you try to cheat by using circuits/wire that's too small where you run into problems. Your also fine just using plugs and receptacles in order to save $$$. I have a couple machines in my shop that "share" receptacles. I try to minimize them, but sometimes you have to do what you have to do

good luck,
JeffD