11
and nuisance overload tripping. If
using a generator, see Technical Data
for generators.
4.5 Three Phase Overload
Protection
Use only Class 10, quick-trip over-
load protection on three-phase
submersible motors. See Definite
Purpose Starters in this manual.
Call the pump manufacturer’s
Customer Service group for selection
assistance.
4.6 Three Phase Power
Unbalance
A full three phase supply consist-
ing of three individual transformers
or one three phase transformer is
recommended. “Open” delta or wye
connections using only two trans-
formers can be used, but are more
likely to cause poor performance,
overload tripping or early motor
failure due to current unbalance.
Check the current in each of the three
motor leads and calculate the current
unbalance as explained below.
If the current unbalance is 2% or
less, leave the leads as connected.
If the current unbalance is more
than 2%, current readings should
be checked on each leg using each
of the three possible hook-ups. Roll
the motor leads across the starter in
the same direction to prevent motor
reversal.
To calculate percent of current
unbalance:
A. Add the three line amp values
together.
B. Divide the sum by three, yield-
ing average current.
C. Pick the amp value which is
furthest from the average current
(either high or low).
D. Determine the difference
between this amp value (furthest
from average) and the average.
E. Divide the difference by the
average.
Multiply the result by 100 to
determine percent of
unbalance.
Hookup
1
Hookup
2
Hookup
3
Starter
Terminals L1 L2 L3 L1 L2 L3 L1 L2 L3
Motor
Leads R B Y Y R B B Y R
T3 T1 T2 T2 T3 T1 T1 T2 T3
Example:
T3-R = 51 amps
T2-Y = 50 amps
T1-B = 50 amps
T1-B = 46 amps
T3-R = 48 amps
T2-Y = 49 amps
T2-Y = 53 amps
T1-B = 52 amps
T3-R = 51 amps
Total = 150 amps
Total = 150 amps
Total = 150 amps
÷ 3 = 50 amps
÷ 3 = 50 amps
÷ 3 = 50 amps
– 46 = 4 amps
– 48 = 2 amps
– 49 = 1 amps
4 ÷ 50 = .08 or 8%
2 ÷ 50 = .04 or 4%
1 ÷ 50 = .02 or 2%
