Preliminary Checks; Current Measurement - Grundfos UPS 26-150 Installation And Operating Instructions Manual

7.2 Preliminary checks

Supply voltage
To check the voltage being supplied to the
motor, use a voltmeter.
Warning
Be careful, since power is still
being supplied to the pump. Do not
touch the voltmeter leads together
while they are in contact with the
power lines.
Single-phase motors
Touch one voltmeter lead to each of the lines
supplying power to the pump as shown in fig. 11:
• L and N for 115 V and 208-230 V circuits
(L = L and N = L for 208-230 V circuits in
1 2
the US)
These tests should give a reading of full line
voltage.
Fig. 11 Testing with voltmeter
Evaluation
When the motor is under load, the voltage
should be within 10 % (+ or -) of the nameplate
voltage.
Any variation larger than this may indicate a
poor electrical supply and can cause damage to
the motor windings. The motor should not be
operated under these conditions. Contact your
power supplier to correct the problem or change
the motor to one requiring the voltage you are
receiving.
12

7.3 Current measurement

To check the current using an ammeter, follow
these steps:
1. Make sure the pump is operating.
2. Set the ammeter to the proper scale.
3. Place the tongs of the ammeter around the
leg to be measured.
4. Compare the results with the amp draw
information on the motor nameplate.
5. Repeat for the other legs.
Fig. 12 Current measurement
Evaluation
If the current draw exceeds the listed nameplate
amps, or if the current imbalance is greater than
5 % between each leg, then check the following:
• The voltage supplied to the pump may be too
high or too low.
• The terminals/wires in the terminal box or to
circuit breaker may be loose.
• The contacts on the motor starter may be
burned.
• The terminals in the starter or terminal box
may be loose.
• There may be a winding defect. Check the
winding and insulation resistance; see
section 7.6 Resistance
• The motor windings may be shorted or
grounded.
• The pump may be damaged in some way
and may be causing a motor overload.
• A voltage supply problem may exist.
tables.