Grundfos SP Installation And Operating Instructions Manual page 23

The percentage of current imbalance can be
calculated by means of the following formulas
and procedures:
Total of current values
measured on each leg
Average
=
current
Greatest amp difference
from the average
% current
=
imbalance
Average current
To determine the percentage of current
imbalance:
1. Measure and record current readings in
amps for each leg (hookup 1). Disconnect
power.
2. Shift or roll the motor leads from left to right
so the submersible drop cable lead that was
on terminal 1 is now on 2, lead on 2 is now
on 3, and lead on 3 is now on 1 (hookup 2).
Rolling the motor leads in this manner will
not reverse the motor rotation. Start the
pump, measure and record current reading
on each leg. Disconnect power.
3. Again shift submersible drop cable leads
from left to right so the lead on terminal 1
goes to 2, 2 to 3 and 3 to 1 (hookup 3). Start
pump, measure and record current reading
on each leg. Disconnect power.
4. Add the values for each hookup.
5. Divide the total by 3 to obtain the average.
6. Compare each single leg reading from the
average to obtain the greatest amp
difference from the average.
7. Divide this difference by the average to
obtain the percentage of imbalance.
Use the wiring hookup which provides the lowest
percentage of imbalance. See section
10.6.3 Correcting for three-phase current
imbalance for a specific example of correcting
for three-phase current imbalance.
7.1.3 Developing the well
After proper rotation and current imbalance have
been checked, start the pump and let it operate
until the water runs clear of sand, silt and other
impurities.
Slowly open the valve in small increments as the
3 water clears until the desired flow rate is
reached. Do not operate the pump beyond its
maximum flow rating.
x 100
If the water is clean and clear when the pump is
first started, open the valve slowly until the
desired flow rate is reached. As the valve is
being opened, check the drawdown to ensure
that the pump is always submerged.
Disconnect the temporary piping arrangements
and complete the final piping connections.
Caution
Start the pump and test the system. Check and
record the voltage and current draw on each
motor lead.
Do not stop the pump until the water
Note
runs clear.
Make sure that the dynamic water
level is always more than 3 feet (0.9
Note
m) above the suction interconnector
of the pump.
CAUTION
Do not operate the pump with the
outlet valve closed. This can result in
motor and pump damage due to
overheating. Install a properly sized
relief valve at the well head to prevent
the pump from running against a
closed valve.
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