3.6.3
Three-Phase Power Imbalance
Current imbalance should not exceed 5% of the average three-phase
current. The current imbalance can be calculated as follows:
STEPS
1.
Measure the current through each of the three legs.
2.
Determine the average of the three currents.
3.
Determine the difference between the current in each leg and the
average of all three legs.
4.
Take the difference with the largest value, and divide it by the average
current. Multiply by 100 to obtain the current imbalance percentage.
5.
If the current imbalance is greater than 5%, “roll” the leads and re-test
(Figure 3.7, “Rolling” the Leads to Balance Current Draw). If “rolling” the
leads does not correct the problem, the source of the imbalance must
be located and corrected. For more information on current imbal-
ance, refer to the motor operation manual.
Figure 3.7
“Rolling” the Leads to
Balance Current Draw
3.6.4
Wire Sizing
For correct power lead sizing from the power source to controls and motor,
refer to the motor installation manual or local electrical codes.
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