Fluke 43B Application Manual page 45

Calculate the current imbalance. Use the same formula as in the
5
previous section but substitute current for voltage.
Current imbalance for three-phase motors should not exceed 10%.
Example
33 A + 29 A
a
1
b 33 A - 32 A
1
29 A - 32 A
2
34 A - 32 A
3
3 A
c
DEVIATION
32 A
AVERAGE
To detect single phasing, always check the current on all three
phases. When a voltage measurement is made at the motor
terminals, the voltages will read close to normal as motor action is
inducing voltage into the open winding.
+ 34 A = 96 A
2 3
3
= 1 A
AVERAGE
= - 3 A
AVERAGE
= 2 A
AVERAGE
x 100% = 9.4 %
Note
Induction Motors
TOTAL
= 32 A
AVERAGE
Largest value: 3 A
Motor Loads 4
DEVIATION
41