Current; How To Measure The Current; Meaning Of Current Measurement; Insulation Resistance - Grundfos CR Serie Instrucciones De Instalación Y Operación

15.2 Current

15.2.1 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.
Fig. 25 Measuring current

15.2.2 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.
24
Remedy
Replace contacts.
Tighten terminals or replace
lead.
Reestablish correct supply
voltage.
Remove cause of short circuit
or grounding.
Replace defective pump parts.

15.3 Insulation resistance

15.3.1 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

15.3.2 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.