Correct Answer: Depends on what service he has

Posted by John T on September 12, 2012 at 05:28:58 from (216.249.82.117):

In Reply to: 220V - 3 phase to 220V - single phase posted by Larry B. 1486 on September 11, 2012 at 18:17:30:

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

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