Maintenance and Troubleshooting of Electric Motors

CHAPTER 2 - Troubleshooting AC Motors

Problem A - Motor won't start or motor accelerates too slowly

A1: Check input power to starter. Is there power on all lines? (Three-phase motors won't start on one-phase.)		Restore power on all lines
A2: Check starter. Is overload protection device opened?		Replace or reset device. Does it open again when starting?
A3: Is there power on all lines to motor?		Repair starter
A4: Is voltage to motor more than 10% below nameplate voltage?		Restore proper voltage.
A5: Check motor terminal connections. Are any loose or broken?		Repair connections.
A6: May be wrong motor for application. Is starting load too high?		Install Design C or Design D motor. Install larger motor.
A7: Is driven machine jammed or overloaded?		Remove jam or overload.
A8: Are misalignments, bad bearings or damaged components causing excessive friction in driven machine or power transmission system?		Repair or replace component.
A9: Are bad bearings, bent shaft, damaged end bells, rubbing fan or rotor or other problem causing excessive friction in the motor?		Repair or replace motor.
A10: Check stator. Are any coils open, shored or grounded?		Repair coil or replace motor.
A11: Check commutator. Are any bars or rings broken?		Replace rotor.

Problem B - Motor runs noisy

B1: Are vibrations and noise from driven machine or power transmission system being transmitted to motor?		Locate source of noise and reduce. Isolate motor with belt drive or elastomeric coupling.
B2: Is a hollow motor foundation acting as a sounding board?		Redesign mounting. Coat foundation underside with sound dampening material.
B3: Check motor mounting. Is it loose?		Tighten. Be sure shaft is aligned.
B4: Is motor mounting even and shaft properly aligned?		Shim feet for even mounting and align shaft.
B5: Is fan hitting or rubbing on stationary part or is object caught in fan housing?		Repair damaged fan, end bell or part causing contact. Remove trash from fan housing.
B6: Is air gap nonuniform or rotor rubbing on stator?		Recenter rotor rubbing on worn bearings or relocate pedestal bearings.
B7: Listen to bearings. Are they noisy?		Lubricate bearings. If still noisy, replace.
B8: Is voltage between phases (three-phase motors) unbalanced?		Balance voltages.
B9: Is three-phase motor operating on one-phase? (Won't start on single-phase.)		Restore power on three-phases.

Problem C - Motor overheats

C1: Is ambient temperature too high?		Reduce ambient, increase ventilation or install larger motor.
C2: Is motor too small for present operating conditions?		Install larger motor.
C3: Is motor started too frequently?		Reduce starting cycle or use larger motor.
C4: Check external frame. Is it covered with dirt which acts as insulation and prevents proper cooling?		Wipe, scrape or vacuum accumulated dirt from frame.
C5: Feel output from air exhaust openings. Is flow light or inconsistent indicating poor ventilation?		Remove obstructions or dirt preventing free circulation of air flow. If needed, clean internal air passages.
C6: Check input current while driving load. Is it excessive indicating an overload?		Go to Step C11.
C7: Is the driven equipment overload?		Reduce load or install larger motor.
C8: Are misalignments, bad bearings or damaged component causing excessive friction in driven machine or power transmission system?		Repair or replace bad components.
C9: Are motor bearings dry?		Lubricate. Does motor still draw excessive current?
C10: Are damaged end bells, rubbing fan, bent shaft or rubbing rotor causing excessive internal friction?		Repair or replace motor.
C11: Are bad bearings causing excessive friction?		Determine cause of bad bearings (See Problem D).
C12: Check phase voltage. Does it vary between phases?		Restore equal voltage on all phases.
C13: Is voltage more than 10% above or 10% below nameplate?		Restore proper voltage or install motor built for the voltage.
C14: Check stator. Are any coils grounded or shorted?		Repair coils or replace motor.

Problem D - Motor bearings run hot or noisy

D1: Check loading. Is excessive side pressure, end loading or vibration overloading bearings?		Reduce overloading.* Install larger motor.
D2: Is sleeve bearing motor mounted on a slant causing end thrust?		Mount horizontally* or install ball bearing motor.
D3: Is bent or misaligned shaft overloading bearings?		Replace bent shaft or align shaft.*
D4: Is loose or damaged end bell overloading shaft?		Tighten or replace end bell.*
D5: Are bearings dry?		Lubricate.*
D6: Is bearing lubricant dirty, contaminated or of wrong grade?		Clean bearings and lubricate with proper grade*
D7: Remove end bells. Are bearings misaligned, worn or damaged?		Replace.
*Bearings may have been damaged. If motor still runs noisy or hot, replace bearings.

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Note: This material is not intended to provide operational instructions.

Appropriate Reliance Industrial Company instruction manuals
and precautions should be studied prior to installation, operation, or
maintenance of equipment.