Three Phase Motors - Grundfos CR Series Installation And Operation Manual

Three Phase Motors

Below is a worksheet for calculating current unbalance on a three-phase hookup and selecting
the proper wiring. Use the calculations in the left-hand column as a guide.
EXPLANATION & EXAMPLES
Here is an example of current readings
at maximum pump loads on each leg of
a three-wire hookup. You must make
calculations for all three hookups.
To begin, add up all three readings for
hookup number 1, 2, and 3.
Divide the total by three to obtain the average.
Calculate the greatest current difference from
the average.
Divide this difference by the average to
obtain the percentage of unbalance.
In this case, the current unblanace for
hookup number 1 is 8%.
Hookup 1
L 1 to T 1 = _ _ _ _ _ _ _ _ Amps
L 2 to T 2 = _ _ _ _ _ _ _ _ Amps
L 3 to T 3 = _ _ _ _ _ _ _ _ Amps
TOTAL = ____ Amps
Hookup 1
_______ Amps
3 _______ Amps
Hookup 1
____ Amps
– ____ Amps
____ Amps
Hookup 1
____ or ____%
____ ____ Amps
T1 = 51 Amps
T2 = 46 Amps
T3 = 53 Amps
TOTAL = 150 Amps
3 150 Amps
50 4.00 Amps
FIGURE HERE
Hookup 2
L 1 to T 3 = ____ Amps
L 2 to T 1 = ____ Amps
L 3 to T 2 = ____ Amps
TOTAL = ____ Amps
Hookup 2
_ _ _ _ _ _ _ _ _ _ _ _ _ _ Amps
3 _ _ _ _ _ _ _ _ _ _ _ _ _ _ Amps
Hookup 2
_ _ _ _ _ _ _ _ Amps
– _ _ _ _ _ _ _ _ Amps
____ Amps
Hookup 2
____ or ____%
____ ____ Amps
Hookup 1
Hookup 1
50 Amps
Hookup 1
50 Amps
– 46 Amps
4 Amps
Hookup 1
.08 or 8%
Hookup 3
L 1 to T 2 = ____ Amps
L 2 to T 3 = ____ Amps
L 3 to T 1 = ____ Amps
TOTAL = ____ Amps
Hookup 3
_ _ _ _ _ _ _ _ _ _ _ _ _ _ Amps
3 _ _ _ _ _ _ _ _ _ _ _ _ _ _ Amps
Hookup 3
_ _ _ _ _ _ _ _ Amps
– _ _ _ _ _ _ _ _ Amps
____ Amps
Hookup 3
____ or ____%
____ ____ Amps
15