New shop has 3-phase service! Running single phase circuits?

[Josh Falcon]

Hi all! I've been a member for a while but just a lurker until now. Anyway, I am moving into a new shop space and am in the process of evaluating my power needs. The space is great but is SEVERELY lacking even basic 115v outlets. My plan is to run a few 115v circuits to get started as well as a 220v line for the Unisaw. I also want to run a 3-phase line for the pin router (Rockwell/SCMI) in the near future.
The space has two breaker boxes, one a 200 amp panel and the other, right next to it a 150 amp panel. Now, I've run 115/220v circuits in the past but never from a panel with three phase service. I've attached a few pics below of the panels. As you can see there's plenty of room to add stuff. Looks like most of the breakers were disconnected at some point. The first pic is the 200 amp box and the 2nd the 150 amp. Am I correct in thinking the 150 amp panel is a main as well?
So, what special considerations (if any) do I need to take to run a few 115v circuits and a 220v? Thanks!

200 amp panel, 150 amp panel
221051221052

[Kirk Poore]

I've only done it the other way (put a 3 ph panel in my garage fed by my RPC), but I think you're best off putting in a single phase subpanel. That way you can use single phase breakers as you normally would.

Kirk

[Jamie Buxton]

If your 3-phase is like mine, it is 208 volts. There are three hots. Each one is 115 volts from ground. You see 208 volts from hot to hot. You can run 115 volt lines from any of the phases. You can run most 230-volt machines from 208, although they'll be a little sluggish to start up. One of my 230-volt machines, a cyclone, would run on 208, but would overheat and shut down in an hour or so. The fix is something called a buck-boost transformer. It is routinely used in the HVAC biz to make 230 volts from 208. You can find them online, or at any local outfit selling to commercial electricians (this means the big-box stores are out).

[Josh Falcon]

Jamie, thanks for the info! I guess that makes this a WYE system? When you say I can run 115v from any of the the three phases, how am I accessing the different hots? How would you isolate just one from the hot buss? I was planning on just running the ground and neutral to the ground/neutral buss and installing the new 20a breaker as normal. I guess it would be nice to know which hot I'm pulling from, I guess?

[Rick Christopherson]

There are two types of 3-phase systems that you could run in to: wye and open delta (center tapped delta). There are benefits and drawbacks to each. I don't see any obvious indications from your pictures to exclude one type over the other. So the best way to verify it is with a volt meter.

On the 120/208 wye system, you will have 208 volts phase-to-phase. This means that your single-phase, 240 volt tools will be running below optimal (and possibly below their rated) voltage. However, the benefit to this system is that you can use any of the 3 phases and neutral to acquire your 120 volt circuits.

On the 120/240 open delta (center tapped delta), you will have 240 volts between phases just like a single-phase system, but one of those phases (the B-phase by code) will have 208 volts from neutral-to-phase. This is called the "stinger" or "high leg", and cannot be used for single-phase circuits.

Aside from avoiding the "high leg", if present, wiring in circuits is no different than a single phase panel.

http://www.rts-engineering.com/tempgraphics/SystemTypes-lo.jpg

[Dan Case LR]

The first thing you need to know--before you change nor connect ANYTHING--is what "flavor" of 3-phase service you have. Measure the voltage between each phase and ground and phase-to-phase.

If you have 1 120/208 (Wye) system, you'll measure 120 to ground from each phase and 208 phase-to-phase. If you have 240 Delta service, you'll measure 120 to ground from two of the phases, and the third phase will be substantially more than 120. Phase-to-phase will measure 240.

For 120V circuits, it doesn't get much easier than 120/208 service--any phase to neutral = 120V. It gets messier when you're dealing with equipment that wants 240 single-phase. Don't just assume that you can run your stuff on 208! Check the nameplates on your motors. Some can be easily rewired for 208, others will tolerate the lower voltage but may not be as efficient, others will live a short and unproductive life that ends in smoke and expletives.

If you have a 120/240 service, you can run your 240V equipment from any two phases. WARNING! for 120V circuits, it's critical that you NOT use the HIGH LEG of the 240 delta. Doing so will shorten the life of most electrically-operated items to seconds at best--short, but with a spectacular end. :)

If you have 3-phase power available, your best bet is to use 3-phase motors wherever possible. The whole system will run happier and at optimal efficiency. I've never seen a 3-phase motor in this voltage class that couldn't be rewired for either 208 or 240, so that part will be easier as well.

One important thing to do is to balance your single-phase loads when feeding them from 3-phase service. In an ideal world, the current demand on all three phases should be equal. In the real world there are times when you can't achieve that, but get as well-balanced as possible.

From the color-coding in the pictures, it appears to be 120/208 service, but I never trust others to use the right color coding. Check it with a meter before you start firing stuff up.

Enjoy!

D.

[Josh Falcon]

Thanks so much for all the great info guys!

I broke out the multimeter this afternoon and took some readings. Unfortunately, they don't seem to jive. I measured each incoming leg (black, red and blue) and got 125v to the ground bus from each. I then got 220v between legs. The few outlets already in place (as well as the installed single pole breakers) all read 125v.

Is my meter giving me false readings? What am I missing?

Thanks again!

[Rod Sheridan]

Hi Josh, either your meter is slightly out or the incoming voltage is slightly high.

Nothing to worry about, you do have a 208 volt wye service so just forge ahead and don't forget to have an inspection performed........Rod.

[Rick Christopherson]

Those numbers indicate that you have a standard 3-phase wye system that is running a little high on the voltage. That's not necessarily bad because it does bring your single-phase phase-to-phase voltages closer to what your tools are expecting.

To that extent, your readings are not unexpected, although I assume you are rounding them up or down. With 125 volts phase-to-neutral, the phase-to-phase voltage should be square-root 3 times that, which is 216 volts.