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[Brian Adams]

I could use some more worldly opinions on this situation. The small shop I've owned for about 2.5 years has a 200A 3-phase Delta service. Obviously it would be better if it had Wye service, but it is what it is, and it would cost me about $8-10k for the city to install a new main transformer installed so that's not gonna happen unless I had a damn good reason. I can find a Delta-to-Wye transformer for about $2k, which is a lot more palatable and would keep the city out of the equation, but I'm not sure that would be the most efficient way to do it.

I'm glad to have two 200A legs for my welders and other tools, but I don't currently use the high leg for anything nor do I have any expectation that I'll ever need to. The Delta service costs me an extra $10 every month, just because it's 3-phase. Not a huge cost, but it's still unnecessary. I can have an electrician swap out the meter, or maybe reconfigure the existing meter to be single phase, which would be a minimal cost and save me $10 a month.

For reference, my shop is roughly 24x36' with the ceiling just over 8'. It's not a huge space, and I use it mostly for storage but I do some wood and metalworking there as well. I doubt I'll ever run anything that needs more than 30A of 240 though. If it was a larger shop it would be a different story, but there's not enough room on the lot to make it bigger (other than going taller or digging out a basement, so not super practical).

If I keep my service the way it is, what potential use might I have for the third leg in the future? I don't own any 3-phase hoists, but if I ever did, I'd want normal 208V motors, so I still couldn't use my high leg. Are there other things I might want to use this existing service for? I guess my question is, should I just get rid of it and change it to single-phase 240, or should I keep it as-is, just in case?

[Don T. Williams]

I was actually able to use my CM 3 phase chain hoists on 3-phase Delta at a venue here.  The city electricians called it 3-phase "wild leg" but it measured out to be 3-phase delta.  It also worked with my 3-phase table saw.  Of course I never hooked my audio distro to that system and always supervised the licensed electrians when the city hired my company.

[Russell Ault]

{...} If I keep my service the way it is, what potential use might I have for the third leg in the future? I don't own any 3-phase hoists, but if I ever did, I'd want normal 208V motors, so I still couldn't use my high leg. Are there other things I might want to use this existing service for? I guess my question is, should I just get rid of it and change it to single-phase 240, or should I keep it as-is, just in case?

My understanding is that a lot of devices wired for three-hots-plus-a-ground (although not all) are rated to handle a phase-to-phase voltage from 208 to 240, which means they should work just fine on a high-leg delta system.

-Russ

[Steve-White]

You already have the best of both worlds.  A 208 system is fine, any single phase equipment will run properly on it.

Save your money and don't do anything.  I'd like to have a Delta system in my shop for an additional $10 a month. 

The 10HP single phase compressor I'm installing recommends a 60A breaker, probably going to test on a 50A.  10HP on a Delta would pull ~25 amps.

EDIT:  Corrected, not 277.

[Geoff Doane]

You already have the best of both worlds.  A 277 system is fine, any 2 phase equipment will run properly on it.

Umm... Where are you getting 277V from?  277 is the phase voltage if you have a 480V 3 phase, 4-wire system.

To Brian:  Is your system an open or closed delta system?  Open delta will only have 2 transformers on the pole, probably a big one for the 120-0-120 phases, and then a smaller one, to give you the "wild" phase.  A "closed" delta, has a third transformer to close that third phase to the other side of the big transformer.  The systems will measure the same, but an open delta is notorious for being unbalanced if there is a heavy load.  Utilities like them because they can save a transformer, and only need to string two high voltage wires, but they can be unstable.  So much so that transmitter manufacturers will not warranty a transmitter that is powered from an open delta system.  It's really only suitable for motors.

Still, being able to test the odd 3 phase device that comes along might be worth it for an extra $10/month.  You might also find that changing the service requires you to do all sorts of other upgrades to be inspected again.  Your electrician would have the answers to that.

GTD

[Jeff Bankston]

I always called it the "kicker" leg. I say keep it. Also I rewired a friends small building that had 2 separate services. A single phase 120/120/N/G residential and a 240/240/240/G 3Ph 4W service for his compressors. That part of the town of Pomona Ca is wired like that as are some other places here in socal. 277 is one leg of 480 with a neutral and used for lighting panels only and a few times I wired a 277 "instahot" made for 277.

[Brian Adams]

Thanks everyone, your advice is very helpful!

I don't know for sure if I have an open or closed system, and I had no idea there was a difference until now. We don't have any overhead power lines in town, and the transformer that feeds my building is in an enclosure just across the alley. It's a single enclosure, with no others in the immediate area, but I don't know exactly what's inside that box. I'll check with the city power guys and see what they say. I'm super curious now.

It's very interesting that CM motors will run on a delta system. If that's the case, that fact alone is worth keeping my service as-is. I doubt I'll ever install a 3-phase table saw or other tool, but you never know. I'd love to have an ironworker, but that's a long shot. I just don't have enough space to have huge tools in this shop and still have any sort of workspace left over. A larger air compressor would be nice someday, and I could find room for that.

Fortunately, if I ever need large tools, a good friend has plenty. A 48" rotary sawmill, a 16" table saw, a 36" planer, a CNC router, a couple large bandsaws. All kinds of goodies. The ironic part is that he has a 100A single phase service and has to use a phase converter to run his 3-phase machines. His sawmill runs on a big CAT diesel engine and the 36" planer has a 4 cylinder gas engine because he doesn't have enough electric power to run them. I don't have space for big machines in my little shop, yet I have more power capacity than I'll ever need. It's weird how things turn out sometimes.

In any case, I'm convinced, the Delta system stays. $10 a month is a small price to pay for what it is. Thanks so much guys!

[Steve-White]

Umm... Where are you getting 277V from?  277 is the phase voltage if you have a 480V 3 phase, 4-wire system.

To Brian:  Is your system an open or closed delta system?  Open delta will only have 2 transformers on the pole, probably a big one for the 120-0-120 phases, and then a smaller one, to give you the "wild" phase.  A "closed" delta, has a third transformer to close that third phase to the other side of the big transformer.  The systems will measure the same, but an open delta is notorious for being unbalanced if there is a heavy load.  Utilities like them because they can save a transformer, and only need to string two high voltage wires, but they can be unstable.  So much so that transmitter manufacturers will not warranty a transmitter that is powered from an open delta system.  It's really only suitable for motors.

Still, being able to test the odd 3 phase device that comes along might be worth it for an extra $10/month.  You might also find that changing the service requires you to do all sorts of other upgrades to be inspected again.  Your electrician would have the answers to that.

GTD

Right you are, thanks.  I don't know what I was thinking - somehow it made sense - but, not 277 to the stinger, 208.  Corrected my post.

[Kevin Graf]

Wild Leg, Red Leg or High Leg Delta, is deriving 120V single phase from a 3 leg Delta system. Jim Brown has a page on the grounding problem of this system.

"Power and Grounding For Audio and Audio/Video Systems"
 'A White Paper for the Real World'
http://www.audiosystemsgroup.com/SurgeXPowerGround.pdf

[Stephen Swaffer]

In any case, I'm convinced, the Delta system stays. $10 a month is a small price to pay for what it is. Thanks so much guys!

Probably a smart choice.  A wild leg delta is designed to run any (properly sized) 3 phase load.  The "wild leg" can only be used for 3 phase loads (or phase to phase single phase loads (208-240 volt)-and that is the only reason it exists.  Where it becomes a problem, is when you feed a 3 phase panel and then hook up single phase to that panel.  If you hook up single phase, phase to neutral (115 VAC) loads to the wild leg bad things will happen.

[ProSoundWeb Community]