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Voltage Imbalance
Voltage imbalances can cause motors to overheat and fail. The maximum voltage imbalance between any two legs
should be no greater than 2%.
Example:
Supply Voltage = 230-3-60
Voltage Readings:
(AB) 224-220 = 4 Volts (Highest Deviation)
(BC) 225-224 = 1 Volts
(AC) 227-224 = 3 Volts
Current Imbalance
A voltage imbalance will cause a current imbalance, but the opposite does not necessarily exist. A loose terminal
connection, buildup of dirt, or carbon on one set of contacts can cause a higher resistance on one leg than on the other
two legs. Current follows the path of least resistance. If terminal connection L1 is loose or dirty, then L2 and / or L3 will
have a higher current. Higher current causes more heat to be generated in the motor windings.
The maximum acceptable current imbalance is 10%.
Example:
Current Readings:
(L1) 96-95 = 1 Amps
(L2) 95-91 = 4 Amps (Highest Deviation)
(L3) 98-95 = 3 Amps
AB = 220 Volts
BC = 225 Volts
Average = (220 + 225 + 227)/3 = 224 Volts
AC = 227 Volts
% Voltage Unbalance = 100 x (4/224) = 1.78% "Acceptable"
!
Contact your local electric utility company
if the supply voltage imbalance exceeds 2%
!
L1 = 96 Amps
L2 = 91 Amps
L3 = 98 Amps
% Current Unbalance = 100 x (4/95) = 4.2% "Acceptable"
CAUTION
!
CAUTION
!
Average = (96 + 91 + 98)/3 = 95Amps
3-5
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