Phase Imbalance Calculator
Calculate three-phase current imbalance percentage and check against NEMA limits.
| Average Current | 100.00 A |
|---|---|
| Max Deviation from Average | 2.00 A |
| Current Imbalance | 2.00% % |
· NEMA method: imbalance = max deviation from average / average x 100.
· Average current: 100.00 A. Max deviation: 2.00 A.
· Voltage imbalance at the source is typically 1/3 to 1/2 the current imbalance shown here.
How It Works
Phase imbalance is calculated using the NEMA method: Imbalance = (maximum deviation from average / average) x 100 For example, if phases read 100 A, 110 A, and 90 A, the average is 100 A, the max deviation is 10 A, and imbalance = 10%. NEMA MG1 recommends that motors not be operated with more than 2% voltage imbalance. Current imbalance at the motor terminals is typically 3 to 5 times the voltage imbalance at the source. Common causes of phase imbalance include unequal single-phase loads on a three-phase system, a faulty connection, or an open phase on utility service.
Example
Average = 100 A. Max deviation = 10 A. Imbalance = 10/100 x 100 = 10%. This level of imbalance would cause serious motor heating and requires investigation.
Frequently Asked Questions
What causes phase imbalance on a 3-phase system?
Unequal distribution of single-phase loads across phases is the most common cause in buildings. Utility transformer issues can also contribute.
What happens if I run a motor with high phase imbalance?
The motor runs hotter. A 2% voltage imbalance can cause a temperature rise of roughly 6 to 10°C above rated values, which shortens insulation life significantly.
How do I fix phase imbalance?
Balance the single-phase loads as evenly as possible across the three phases. For feeder-level imbalance, check for loose connections or call the utility.