Preliminary Electrical Tests - Grundfos CR Installation And Operating Instruction Manual

13. Preliminary electrical tests

Warning
When working with electrical circuits, use caution
to avoid electrical shock. It is recommended that
rubber gloves and boots be worn, and metal
terminal boxes and motors are grounded before
any work is done. For your protection, always
disconnect the pump from its power source
before handling.
13.1 Supply voltage
13.1.1 How to measure the supply voltage
Use a voltmeter, (set to the proper scale) measure the voltage at
the pump terminal box or starter.
On single-phase units, measure between power leads L1 and L2
(or L1 and N for 115 volt units).
On three-phase units, measure between:
– Power leads L1 and L2
– Power leads L2 and L3
– Power leads L3 and L1
Fig. 24 Measuring supply voltage
13.1.2 What the supply voltage measurement means
When the motor is under load, the voltage should be within ±10%
of the nameplate voltage. Larger voltage variation may cause
winding damage.
Large variations in the voltage indicate a poor electrical supply
and the pump should not be operated until these variations have
been corrected.
If the voltage constantly remains high or low, the motor should be
changed to the correct supply voltage.
13.2 Current measurement
13.2.1 How to measure the current
Use an ammeter (set on the proper scale) to measure the current
on each power lead at the terminal box or starter. See the motor
nameplate for amp draw information.
Current should be measured when the pump is operating at
constant discharge pressure.
20
Fig. 25 Measuring current
13.2.2 What the current measurement means
If the amp draw exceeds the listed service factor amps (SFA) or if
the current imbalance is greater than 5% between each leg on
three-phase units, check the following:
– Burned contacts on motor starter.
– Loose terminals in starter or terminal box or possible wire
defect.
– Too high or too low supply voltage.
– Motor windings are shorted or grounded. Check winding and
insulation resistances.
– Pump is damaged causing a motor overload.
13.3 Insulation resistance
13.3.1 How to measure the insulation resistance
Turn off power and disconnect the supply power leads in the
pump terminal box. Using an ohm or mega ohm meter, set the
scale selector to Rx 100K and zero adjust the meter.
Measure and record the resistance between each of the terminals
and ground.
Fig. 26 Measuring insulation resistance
13.3.2 What the insulation resistance means
Motors of all hp, voltage, phase and cycle duties have the same
value of insulation resistance. Resistance values for new motors
must exceed 1,000,000 ohms. If they do not, motor should be
repaired or replaced.