3 phase question

WyoDave

Well-known Member
I'm building a new house, near my shop. It's going to require an electrical upgrade, and my plan is to have the COOP drop a 120/208 3 phase Y, and run this to my shop, and to the new house. That way I can stay with one meter. I see a lot of things like ovens, clothes dryers, air conditioners etc... are able to run either 240 or 208. Will they just have lower output, or is it something you can select, and still get full power out of them? Is this something I'll regret? Obviously the main benefit is having 3 phase in the shop.

David
 
(quoted from post at 11:36:14 10/24/13) I'm building a new house, near my shop. It's going to require an electrical upgrade, and my plan is to have the COOP drop a 120/208 3 phase Y, and run this to my shop, and to the new house. That way I can stay with one meter. I see a lot of things like ovens, clothes dryers, air conditioners etc... are able to run either 240 or 208. Will they just have lower output, or is it something you can select, and still get full power out of them? Is this something I'll regret? Obviously the main benefit is having 3 phase in the shop.

David
efore you spend too much time investigating equipment, you best talk to your co-op to see if they will do what you want & what the cost to you will be. Probably going to be a surprise!
 
It runs right by the shop to an irrigation service anyways. They just have to do the drop. I already talked to them.

David
 
Electric heaters operated on 208 instead of 240 will produce approx 75% of nameplate heat. 208 instead of 220v will drop output to 89% . So the operator of an electric stove or clothes dryer would never notice the difference unless operated continuous at 100%.
Single phase well pumps and AC units will usually slug along ok on 208V as manufactures make some allowances.
Ideally the house AC and well pump would be three phase 208. Motor efficiency will be much improved over the single phase versions of the same capacity .
 
208 is an oddball for a home, just put in the appropriate transformer and run the home on 240/120.
 
Thanks. The only problem I might have is I found a real nice deal on an air conditioner that isn't 3 phase. It is marked 208/230v single phase. Will it work alright? I understand the benefit behind finding a 3 phase unit, but the price is right on the one I found.
David
 
The only thing that should be sized as 208 only is probably the hot water heater. Otherwise you may have to wait some for hot water if it is rated 240 and operated 208. In my area the power company supplies 120/208 and most things work fine [although it is changing amperage ]. The 277/480 from Public Service is really 265/460 volts . They are ripping everyone off a little . All equipment installed is rated for 277/480 and operates normally.If you google search this you can ad alot of confusion from some of the electrical websites where everyone argues about what works and what doesn't..
Allegedly manufacturers are allowing for this in appliances.
 
Any one phase to neutral is 120. It is a 120/208 3 ph service. Single pole breaker taking one position are still 120 output.two pole and 3 pole breakers will put out the 208 voltage.
 
Thanks. Gas hot water heater, so that shouldn't be a concern. I know exactly what you mean about arguing on other sites. I'm going to have a meeting with the COOP and my electrician next week, and go over the plan. Just want to sound like I know what I'm talking about a little bit in the meeting.

David
 
Best way to impress people in those type meetings is to wear a hard hat wrapped in tin foil with some coat hanger or welding rod antennas.They will just assume you are some type of engineer or electrical genius. Please post pics after the meeting Thanks.
 
You may want to look at the rate structure too. The three phase service will likely be a commercial rate and could also include a demand charge. this could make your residential use actually more expensive than a seperate single phase service. Also consider voltage drop loss from your shop to the house and the maintainence cost if it is your wiring.

Also, if you deduct the shop power as a business expense you will have problems with the IRS if the house consumption is not metered by a real electric meter. I did it the other way around and fed my shop from the house service through my own sub meter. I read the meters every Jan 1 and deducted the percentage of use for the shop from my household expense.
 
Just make sure you are either setting down or have something soft to fall on when they give you the price.
 
Cost per kWh is the same. The 3 phase basic charge is more, but I want it for my shop anyways. The only thing is I will be losing the single phase basic charge. It isn't huge, but it adds up. Also, I didn't explain it very well. Both buildings will be fed separately but from the same meter location.

David
 
A 32 volt buck is designed for 208-240 conversion. I'm not sure that I would go with the system you're talking of for a house though. Have you got that much 3 phase equipment? What you will probably get is an open delta system, not Y. VFD's could be cheaper and more beneficial unless you have a lot of equipment.
 
Okay, heres the deal, but this is how it was when I was an electrical power distribution design engineer and things may have since changed so no warranty.

SOME equipment is labeled and designed to operate at EITHER 208 OR 240 while some IS NOT, so the correct engineering answer is IT DEPENDS. That being said, much of equipment will still operate at EITHER even if not so labeled perhaps not as efficient or as much output if operated at a reduced voltage.........

The ONLY time I specified 208 Y 120 volt three phase four wire was for say an office complex (NOT an industrial application) where the majority of the load was 120 volt single phase but the HVAC was operated at 208 volt three phase with compressors and air handlers designed for use at 208 and clearly labeled as such.

The more typical industrial service was 480 Y 277 three phase four wire in which case I specified 277 volt lighting and used a dry transformer to get the needed 120 volt single phase

As some correctly stated, on the 208 Y 120 volt three phase four wires system its 120 volt from any leg to Neutral (3 legs of 120) but 208 from any line to other line since 120 x square root of 3 (1.732) = 208.

The thing is I see ALOT MORE 240 volt three phase equipment then I do 208 since 240 is more the standard then 208 although sure, "much" equipment can still work at reduced voltage

If I had my druthers and I needed a lot of three phase 240 (more typical equipment) instead of 208 plus still some 120 Id opt for maybe the 120/240 volt three phase four wire High/Red leg Delta system.

THE CORRECT ENGINEERIGN AMSWER DEPENDS ON THE LOADS AND USES AND HOW MUCH 3 VERSUS SINGLE PHASE EQUIPMENT YOU WILL USE and that cant be answered without first knowing all that. Sure Billy Bob and Bubba can render an opinion or what worked best for their shop/home but that may or may NOT be best for your individual situation

NOTE I do like the idea of three phase but 208 isn't my first choice of voltage, that would be 240 for small shop/farm use.....

Your money your choice, CHECK WITH THE UTILITY PROVIDER and do a little design and leg work as to your loads and uses and the equipment youre gonna operate is my engineering advice ......

John T
 
John T--in my past experience in working with older Y circuits for bridge power we quite often came across the problem of a HIGH Leg--where one of the legs to neutral was quite higher than 120 V. Would this be of a concern here??
 
Thanks John. I understand exactly what you're saying. I was thinking originally for 2 meters. A standard 120/240 single phase to feed the house, and then a 120/240 delta 3 phase for the shop. Then I thought just go with the 120/208 for both and only have one meter. I'm not too crazy about the idea of a 120/240 high leg 3 phase power in the house since that could confuse some electrician down the road with that high leg. I think they'd be more apt to check for it in a shop building. What are the guidelines behind having a 120/240v 3 phase service and only feeding the two 120v legs to the house? Just not hooking up the wild leg? Is that major violation, or something the provider will be against? Kinda thinking out loud.

David
 
I am NOT an electrician.....But.....I do know that there is a piece of equipment that MUST have 208 3phase at where I work. This machine has it's own transformer to supply 208 off of the 240 VAC supplied.
I think that every machine has to be looked at as an individual system. I would think that 95% of anything you have in your shop or in the house, like a dryer or stove, that needs a higher voltage would be okay to run within 5 or 10% of the 230VAC supplied.
 
Hey there Dave, I see from your response you certainly understand the benefits or pitfalls of the 208 or red leg system, you're NO Billy Bob!!!

Heres my experience. Actually any half A$$ real electrician knows and well understands the red leg system, they have seen it in industrial applications if they have ever done much work at all and aren't confused or dangerous if all is configured and labeled correctly. Our electricians labeled and red taped any high legs in all panels plus clearly labeled the panelboards.

NOTE for the house you don't have any red leg problem, you run 4 wires to it, the two hots (from that center tapped transformer), Neutral, and Equipment Ground. Theres no red leg even ran to the house, its feed is same as all other houses, simply a 120/240 center tapped transformer THATS NO BIG DEAL every other home in the neighborhood is fed from a 120/240 center tapped transformer!!!!!!!


HOWEVER when I specified that system it was in a primarily industrial application where I had a chance to balance the 3 transformers and there was a lot more 240 loads (both single and 3 phase) then the 120 which was for the office to run on. But if you don't use much 240 those other two transformers are just gonna be sittin there wasting heat energy while the one center tapped transformer that feeds your house doin all the work.

This is why I talked about the choice depending on the loads. I'm just not a fan of the 208 Y 120 for a shop or farm where most of the equipment choices are better suited to 240 then 208, although most will still work

Talk to the utility provider and get a good handle on the equipment youre gonna be using and see if 208 or 240 will work and then make the decision. I don't want to discourage your from three phase, its best, but just take a look at your actual loads before making the decision is my best albeit rusty engineering advice. Again, any real electrician isn't confused by that system so I wouldn't worry that much over that, just be sure all is well labeled

John T
 
In the Y system (208 Y 120 volt three phase four wire) theres no higher leg, all are 120 to Neutral or 208 phase to phase. ITS ONLY IN THE DELTA (120/240 volt three phase four wire center tapped DELTA) where two legs are 120 to neutral while the red/high leg is 208 to neutral BUT THATS NEVER USED ANYWAY......

Got it??????? If not post back

John T
 
Thank again, and for the record I am a Billy Bob. Just been around a lot of 3 phase for irrigation purposes, and it's a little of this, or a little of that. We have 277/480 wye and 480 corner grounded. 120/240 delta red leg. 240 corner grounded. No 120/208 wye though. Almost want to add it, so I have them all. Haha. Thanks again.

David
 
Since I'm not a fan of floating Delta at our facility I specified the very first corner grounded straight delta that was ever used. Shortly after one of the electricians came to me all excited saying he put his meter on each leg to ground and one (of the 3) of them WAS DEAD, ZERO VOLTS

I say well duhhhhhhhhhhhhhhhh lol wonder how that happened hmmmmmmmmmmmmm

John T
 
I've never been around an ungrounded system. My Dad has mentioned having them, but the power company changed them out before I worked on anything. Thanks for the advise. I'll let you know what I end up doing.

David
 
THANKS!!--my memory is failing and we did have delta supply circuits---I remember that high leg very well after we blew some relays!!
 
Using two phases to run 120/208 to the house will work as this is done in most apartment type buildings where I live (Florida). The coop may prefer to furnish an open delta service using two transformers as this would be most cost effective for the coop.
 
To my knowledge unless something has changed, no one provides or delivers 3-phase to residential, period. Perhaps something has changed. They sure will not by me. Never have.

Mark
 
I work for a coop which will and does supply three phase services to residential houses. Almost all are open delta.
 
(quoted from post at 06:27:39 10/25/13) To my knowledge unless something has changed, no one provides or delivers 3-phase to residential, period. Perhaps something has changed. They sure will not by me. Never have.

Mark

Yeah I think what he wants will require 2 separate services.
 
Out by me in Indiana, residential isn't offered 3-phase. When I lived in Illinois, same thing. I can't think of a residential item that requires 3-phase, making running 3-phase cost prohibitive for the power guys and probably why its not offered anywhere near me. Don't get me wrong, 3-phase is certainly available by me for commercial, industrial, or AG (irrigation for example) and they have their own meters. For future reference to help me understand, what sort of residential item requires 3-phase?

Thanks.

Mark
 
Better check with the COOP, they will have to furnish the multiple transformers for 3 phase and might want a minimum usage fee to do this.

How much 3 phase equipment do you have, or plan to have?
 
Years ago local folks said 3 phase was way to go for our dairy barn.Cheaper trouble free motors rate per kw would be same.However with having to have two meters we were charged the high rate on 2 meters for first kws used instead of only one time on higer rates an thereafter on sliding rate. An!!!!!!!we were not told there would be a charge for the demand meter that was reset every month an i think it was as much as the actual kw used. End result was electric was a very high cost for total kw used.Be aware !!
 
He only needs ONE service. He can get BOTH 120 VAC Single Phase PLUS 240 Three Phase PLUS 240 Volt Single Phase from a single 120/240 volt three phase four wire center tapped delta service

OR From another only ONE service he can get 208Y 120 volt three phase four wire.

Hope this helps

John T
 
Teaneck [a town near me] has many residential 3 phase services for the AC units. However every time my old boss ordered a panel for one of these homes doing a service upgrade garranteed he would forget and you would have to go back to the supply house for the three phase panel and return the single phase.. You would think after several years he would remember . not once.
 

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