AIM Manual

Motor Maintenance » Single-Phase Motors and Controls (Page 48)

Identification Of Cables When Color Code Is Unknown (Single-Phase 3-Wire Units)

  • If the colors on the individual drop cables cannot be found with an ohmmeter, measure:
  • Cable 1 to Cable 2
  • Cable 2 to Cable 3
  • Cable 3 to Cable 1
  • Find the highest resistance reading.
  • The lead not used in the highest reading is the yellow lead.
  • Use the yellow lead and each of the other two leads to get two readings:
  • Highest is the red lead.
  • Lowest is the black lead.
  • Example: The ohmmeter readings were:
  • Cable 1 to Cable 2 - 6 ohms
  • Cable 2 to Cable 3 - 2 ohms
  • Cable 3 to Cable 1 - 4 ohms
  • The lead not used in the highest reading (6 ohms) was
  • Cable 3—Yellow
  • From the yellow lead, the highest reading (4 ohms) was
  • To Cable 1—Red
  • From the yellow lead, the lowest reading (2 ohms) was
  • To Cable 2—Black

Single-Phase Control Boxes

Checking and Repairing Procedures (Power On)

WARNING: Power must be on for these tests. Do not touch any live parts.

  • A. VOLTAGE MEASUREMENTS
  • Step 1. Motor Off
  • 1. Measure voltage at L1 and L2 of pressure switch or line contactor.
  • 2. Voltage Reading: Should be ± 10% of motor rating.
  • Step 2. Motor Running
  • 1. Measure voltage at load side of pressure switch or line contactor with pump running.
  • 2. Voltage Reading: Should remain the same except for slight dip on starting. Excessive voltage drop can be caused by loose connections, bad contacts, ground faults, or inadequate power supply.
  • 3. Relay chatter is caused by low voltage or ground faults.
  • B. CURRENT (AMP) MEASUREMENTS
  • 1. Measure current on all motor leads.
  • 2. Amp Reading: Current in red lead should momentarily be high, then drop within one second to values in Table 13. This verifies relay or solid state relay operation. Current in black and yellow leads should not exceed values in Table 13.
  • 3. Relay or switch failures will cause red lead current to remain high and overload tripping.
  • 4. Open run capacitor(s) will cause amps to be higher than normal in the black and yellow motor leads and lower than normal in the red motor lead.
  • 5. A bound pump will cause locked rotor amps and overloading tripping.
  • 6. Low amps may be caused by pump running at shut-off, worn pump, or stripped splines.
  • 7. Failed start capacitor or open switch/relay are indicated if the red lead current is not momentarily high at starting.

Caution: The tests in this manual for components such as capacitors, relays, and QD switches should be regarded as indicative and not as conclusive. For example, a capacitor may test good (not open, not shorted) but may have lost some of its capacitance and may no longer be able to perform its function.