Current Measurement; Insulation Resistance - Grundfos CR Series Installation And Operation Manual

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 BEFORE HANDLING.
Preliminary tests
Supply
voltage
Current
measurement
Insulation
Resistance
12
How to measure
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
How to Measure
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.
How to Measure
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.
What it means
When the motor is under load, the
voltage should be within ±10% of the
nameplate voltage. Larger voltage varia-
tion may cause winding damage.
Large variations in the
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.
What it Means
If the amp draw exceeds the listed service
factor amps (SFA) or if the current imbal-
ance is greater than 5% between each leg on
three-phase units, check the following:
1. Burned contacts on motor starter.
2. Loose terminals in starter or terminal
box or possible wire defect.
3. Too high or too low supply voltage.
4. Motor windings are shorted or
grounded. Check winding and insula-
tion resistances.
5. Pump is damaged causing a motor
overload.
What it 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.
voltage