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UNBALANCED 3-PHASE SUPPLY VOLTAGE —
Use the following formula to determine the percent voltage
imbalance:
% Voltage Imbalance =
100 x
max voltage deviation from average voltage
average voltage
EXAMPLE: Supply voltage is 240-3-60.
AB = 243 v
BC = 236 v
AC = 238 v
Average Voltage = 243 + 236 + 238
3
= 239 v
Determine maximum deviation from average voltage:
(AB) 243 – 239 = 4 v
(BC) 239 – 236 = 3 v
(AC) 239 – 238 = 1 v
Maximum deviation is 4 v.
Determine percent voltage imbalance:
% Voltage Imbalance = 100 x
4
239
= 1.7%
This amount of phase imbalance is satisfactory as it is below
the maximum allowable 2%.
IMPORTANT: If the supply voltage phase imbalance
is more than 2%, contact your local utility company
immediately.
