RE: 3 phase question

First off I want to say Thank You for all the replies. Secondly I never said this 3 phase panel was at my residence! It's TRULY a 3 phase system, I know for a FACT! I'm trying to wire a 3 phase a/c unit to one of the COMMERCIAL buildings I own. The hvac guy is telling me the unit is showing out of phase, so we switched legs as was told by a tech. Didn't help So I was wondering if the high leg had something to do with the problem. I got the 203/230 numbers off the a/c unit. Maybe I misread the voltages. But Thanks anyway.

Phase to phase voltages are all the same, regardless of 'high leg' (that becomes a concern when selecting leg for single phase leg-to-neutral). Phase rotation is reversed by swapping any two of the three wires (phase wires).

Thanks for the feedback and new info, that helps us help you. The answers previously given were based on the info we had then and the guesses we had to make not being there.


"It's TRULY a 3 phase system, I know for a FACT! I'm trying to wire a 3 phase a/c unit to one of the COMMERCIAL buildings I own."

NOT a problem, as a few of us said before, if you have a 3 phase panel, all it takes is a 3 pole circuit breaker to supply the 240 Volt Three Phase Power.

"The hvac guy is telling me the unit is showing out of phase, so we switched legs as was told by a tech. Didn't help"

If its out of phase and therefore say a motor is turning in the wrong direction, if you reverse any two of the legs it reverses direction and gets it back in phase. If it didnt cure out of phase I have no answer for you as every 3 phase motor I ever saw reversed if any two legs were swapped.

"So I was wondering if the high leg had something to do with the problem."

NOPE its 240 volt three phase on the three corners of the Delta and the fact one of the transformers is center tapped (to get 120) doesnt change that BEING A HIGH LEG SYSTEM ISNT THE PROBLEM as far as 240 volt three phase is concerned.


"I got the 203/230 numbers off the a/c unit"

Previously we weren't told that. What that new info tells me is the unit is designed such that it can operate and tolerate in the voltage range from 208 to 230. Not alllllllll motors are labeled or designed as such. Some are 208 some are 240 while yours appears can work on either. Also a 208 volt Y system IS NOT the same as the 240 volt Delta system.

Hope this helps

John T retired Electrical Engineer

Does this a/c unit have a phase monitor factory installed that is indicating unit is out of phase if so and you have switched two leads and it still shows out of phase then the phase monitor may be bad. If it does have a phase monitor have you tried bypassing it and see if unit will run and check rotation of compressor and condenser motor. If this unit has a helical screw compressor DO NOT try this but if it is a scroll compressor you can run it for a short period of time and check the pressures. If it does not show a differential pressure and is very noisey it is running backwards. Not knowing what unit you have it could have a single phase condenser fan and that would tell you also if it is reversed.

Phase monitors often have an adjustment for sensitivity, and some can trip for unequal legs.

That's a very good point Tramway Guy the monitor could see the high leg and lock it out on unequal line voltage that's why I suggested bypassing it. It depends on what phase monitor if it gives a code for lockout or just has a light to indicate proper phasing

As previously mentioned, the wild leg shouldn't affect the three phase compressor. However, if you control voltage is picked up on that leg, it might cause a problem.
Pete