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 overload
protection on three-phase submers-
ible motors. See Denite Purpose
Starters in this manual.
Call the pump manufacturer’s Cus-
tomer Service group for selection
assistance.
4.6 Three Phase Power
Unbalance
A full three phase supply consisting of
three individual transformers or one
three phase transformer is recom-
mended. “Open” delta or wye con-
nections using only two transformers
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, yielding
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%
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