WiremanWireman · Controls & drives troubleshooting · 2023 NEC ·
Controls & drives
Contactors, starters, relays, VFDs, sensors, PLC I/O.
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Contactor won’t pull in or chattersTrace the control circuit, find the open device, check the coil.Up to 2 stepsMotor won’t stop (welded contacts)Make it safe first, then find out whether the contactor is stuck or the control circuit is still calling.Up to 4 stepsMotor runs only while start is heldThe holding contact isn’t sealing the start button in. Find out whether it’s the contact, the wiring or a jog setting.Up to 4 stepsControl fuse keeps blowingSeparate a real short or ground fault from a fuse that’s too small for coil inrush.Up to 3 stepsRelay or timer not workingCoil voltage first, then the contacts, then the timing mode and settings.Up to 3 stepsFloat or pressure switch pump controlPump won’t start, won’t stop or short-cycles: check the switch, then what it’s sensing.Up to 3 stepsReversing starter problemsOne direction dead, fuses or breakers on reversal, or wrong rotation both ways.Up to 3 stepsSoft starter faultsGeneric fault categories: supply, SCRs, bypass, start settings and load.Up to 2 stepsVFD overcurrent faultWhen the fault happens tells you whether it’s the ramp, the load, or a short on the drive output.Up to 4 stepsVFD overvoltage or undervoltage faultDC bus too high is usually deceleration; too low is usually the supply.Up to 4 stepsVFD ground faultTest the motor and leads with the drive disconnected, then look at cable length and wet conduit.Up to 3 stepsVFD overheatingFans, dirty heatsinks, a hot enclosure or a drive working too hard.Up to 4 stepsPLC input not seenVoltage at the input terminal, the input LED, then the program.Up to 3 stepsPLC output not workingLED versus actual voltage at the terminal, then the field wiring and the load.Up to 3 steps4–20 mA sensor reading wrongMeasure the loop current, then decide whether it’s the transmitter, the loop or the scaling.Up to 2 stepsPhoto-eye or proximity sensor not detectingPower, the sensor’s own LED, the output, then alignment and target.Up to 3 steps