Preliminary Electrical Tests; Supply Voltage; Current; Insulation Resistance - Grundfos CR Installation And Operating Instructions Manual

17. Preliminary electrical tests

DANGER
Electric shock
Death or serious personal injury
- Before starting any work on the product, make
sure that the power supply has been switched off
and that it cannot be accidentally switched on.
- We recommend to wear rubber gloves and boots,
and to make sure that metal terminal boxes and
motors are grounded before any work is done.

17.1 Supply voltage

17.1.1 How to measure the supply voltage
Use a voltmeter (set to the proper scale) to 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
17.1.2 Meaning of supply voltage measurement
When the motor is under load, the voltage should be within + 10
%/- 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.

17.2 Current

17.2.1 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 outlet
pressure.
Fig. 25 Measuring current
28
17.2.2 Meaning of current measurement
If the amp draw exceeds the listed service factor amps (SFA) or if
the current unbalance is greater than 5 % between each leg on
three-phase units, check for the following faults:
Fault
Burned contacts in the motor-
protective circuit breaker.
Loose terminals in motor-protective
circuit breaker or terminal box or
possibly defective lead.
Too high or too low supply voltage.
Motor windings are short-circuited
or grounded. (Check winding and
insulation resistances).
Pump is damaged causing motor
overload.

17.3 Insulation resistance

17.3.1 How to measure the insulation resistance
Turn off power and disconnect the supply power leads in the
pump terminal box. Using an ohmmeter or megohmmeter, set the
scale selector to R x 100K and zero-adjust the meter. Measure
and record the resistance between each of the terminals and
ground.
Fig. 26 Measuring insulation resistance
17.3.2 Meaning of insulation resistance measurement
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, the motor should be
repaired or replaced.
Remedy
Replace contacts.
Tighten terminals or
replace lead.
Reestablish correct supply
voltage.
Remove cause of short
circuit or grounding.
Replace defective pump
parts.