3 phase voltage imbalance

[rhb9972]

This 40 year old building electrical service enterance updated 3years ago to 480V 3 phase to three transformers to a labeled panel of 3 phase 230V with several 3 phase motors wired to this panel.
AC meter readings of each phase to netural produce a reading of 230V on the 1st phase 120V on the 2nd phase and 120V on the 3rd phase.
I have never seen this before, is this ok to run 3 phase motors this way.

 

[don_resqcapt19]

Re: 3 phase voltage imbalance

What voltage do you get when you read between the hots? This sounds like a 120/240 3 phase 4 wire delta system. In this system 2 of the 3 hots will read 120 volts to the grounded (neutral) conductor and the third will read 208 volts the the grounded conductor. You should read 240 volts between each of the hots. If the voltages between the hots are the same and approximately 240 volts there is no problem. The 3 phase motor doesn't care about the voltage to the grounded conductor, it only sees the voltage between the hots.
Don

 

[mark]

Re: 3 phase voltage imbalance

Sounds to me like you are dealing w/ a 3-phase, 3-wire ungrounded system. The ungrounded conductors will not recognize ground because there is not a ground reference in the X-Frmr. Check your voltage between phases not to ground.

 

[rhb9972]

Re: 3 phase voltage imbalance

The voltage between the phases range from 230V (between the two 120V to ground) and up to 260V (between the 230V to ground and the 120V).