220V - 3 phase to 220V - single phase

[Larry B. 1486]

My brother in law bought this properety that has a shop with a 220-3 phase line running into it. To run a regular 220V single phase motor, will it work to just tie into two of the three hot wires to make it work because are they not 110 lines? Doesn't one of the hot wires in a 3 phase have more than 110 volts running thru it?
 

[David G]

No, they are 120 degrees apart on phase versus 180 on single phase.
 

[David G]

Are you sure it is not 208/120 3 phase?
 

[BenAlbert]

Hopefully I can explain this so it is understandable. From one of the legs to neutral will be about 170 V. This is because the neutral is connected half way between the other two legs (at the utility Co. end). This way you get 220 V between each of the three legs and 110 v from two of the legs to neutral. You can run 220v from any pair, just be sure not to try to split it for a motor starter etc.
 

[JMOR]

[George Marsh]

Larry,
What size 3 phase motor do you need? I think I have a 3 or 5 hp.
George
 

[MarkB_MI]

JMOR is correct. You need to figure out what you have. It could be 240 hi-leg delta, it could be 120/208 wye, or it might be something else.
 

[Uncle Ernie]

It will work just fine as long as you measure voltage from each phase to neutral and use the two that measure 120 VAC to neutral. If all three measure 120 to neutral you can use any two.
 

[John T]

Larry, heres the entire picture and real deal:

QUESTION

"will it work to just tie into two of the three hot wires to make it work because are they not 110 lines?"

ANSWER

IT DEPENDS ON WHAT SERVICE HE HAS

A) If his incoming service is 120/240 volt Three Phase Four wire center tapped (Red or High Leg) DELTA ORRRRRRRRRRRRR 240 volt three phase three wire straight DELTA (which I doubt since he likely has BOTH 120 and 240 service)

YES theres 240 volt single phase across any of the three Delta transformers (NOT talkin any leg to Neutral if it has one transformer center tapped) and wiring across any delta winding will power a 240 volt single phase motor WELL DUHHHH its 240 volts across any of the three delta connected transformers......

HOWEVER one practice (in addition to load balancing) is to run single phase 240 volt loads off either of the two non center tapped windings instead of using the winding that has the center tap, as its often used for two legs of 120 and of course, for 240 volt three phase loads.

B) If his incoming service is 208 Y 120 Volt Three Phase Four Wire, there exists 120 from any leg to Neutral and 208 from any leg to any other leg. That means a 208 three phase motor can run off the three legs for 208 3 Phase while a 208 volt single phase motor can be powered by any two of the three legs, Line to Line (any Line) is 208 single phase.

NOTE depending on the motor design and rating and load, some motors could operate at EITHER 208 or 240

SOOOOOOOOOOOOOOOOOOO if his service is a 240 volt DELTA, any 2 windings (but often NOT the one center tapped) will power a 240 volt single phase motor.........BUT if its a 208 Y 120 Volt Three Phase Four Wire service, any 2 legs will provide 208 (which may still work??) BUT NOT 240

QUESTION

"Doesn't one of the hot wires in a 3 phase have more than 110 volts running thru it?"

ANSWER

I'm not sure thats a correct question

Three phase service can be EITHER:

1) 240 volt 3 phase 3 wire Delta (has NO 120)

2) 120/240 volt 3 phase 4 wire center tapped Delta know as the Red Leg or High leg system has 240 3 phase,,,,,,,,240 single phase across any two legs,,,,,,,,120 single phase from either end of the center tapped leg to Neutral, but its 208 (120 x 1.732) from the High or Red leg to Neutral

3) 208 Y 120 Volt 3 phase 4 wire has 120 from any of the three legs to Neutral,,,,,,,,208 single phase across any two L to L legs,,,,,,,,,208 volt 3 phase across L1 L2 L3

NOTE I did NOT address any of the two transformer open delta configurations as I doubt he has that but such do exist

NOTE Its NOT rocket scient to just looh up on the pole and see how his three transformers are configured Y or Delta !!!!!!!!!!!! ORRRRRRRRR look inside his main panel or use a volt meter to see if he has 208 or 240 service

PS dont be concerend if you dont undertand all this, most non trained or non experienced electrical people (except maybe for Billy Bob and Bubba lol) dont either

Hope this helps, post back any questions

Best wishes n God Bless

John T Too long retired EE and rusty on latest codes and practices but believe the above to still be true
 

[David G]

Bottom line, pay a licensed electrician to evaluate and give you the correct answer, all of us are guessing what service you have.
 

[John T]

Darn good answer, its extremely easy to just look on the pole at how the transformers are wired (Y or Delta) or use a simple AC Voltmeter, but if hes totally inexperienced or dont have a meter or a clue, you are soooooooo right......

If its 3 phase Delta theres 240 single phase from any L to any other L and if its 208 Y 120 theres 208 from any L to any other L so he has a good chance at operating a single phase motor, its only that if he has 208 some 240 motors may or may not be happy lol

John T
 

[c.hess]

First i am not a electrician but did have farm experience with 3 an single phase having quiet a few 2---7.5 hp motors on Harvestore mistakes.My tool was two light bulbs connected for testing 120 or 240 volts.What i really want to advise is our area at 30 0r so years ago when electric co installed 3phase we were billed the higher rate for current twice as they installed another meter(one for house one for barn) futhermore we were billed so much for demannd in addition to kw used.Demand was reset every month.Dont know if that is still true but needs to be in equasion if anyone is thinking of installing 3phase.
 

[c.hess]

First i am not a electrician but did have farm experience with 3 an single phase having quiet a few 2---7.5 hp motors on Harvestore mistakes.My tool was two light bulbs connected for testing 120 or 240 volts.What i really want to advise is our area at 30 0r so years ago when electric co installed 3phase we were billed the higher rate for current twice as they installed another meter(one for house one for barn) futhermore we were billed so much for demannd in addition to kw used.Demand was reset every month.Dont know if that is still true but needs to be in equasion if anyone is thinking of installing 3phase.
 

[John T]

Good point, in a three phase system the power is Volts x Amps X 1.732 (for unity one power factor) versus Volts x Amps if only single phase. However three phase motors are efficient and self starting. At our facility we also had to pay a hugeeeeeeeee power factor penalty they referred to as an energy charge, which is why we installed a bunch of power factor correction capacitors. Given theres often 3 phase machinery sold at auction which most farmers cant use, the price can be very good if you have 3 phase power available, or else one can use a rotary or solid state device.....

John T