Troubleshoot AC Motors
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The following charts will give you multiple pathways to assist when you are attempting to troubleshoot AC Motors. The 4 problems covered are:
- Problem A – Motor won’t start or motor accelerates too slowly
- Problem B – Motor runs noisy
- Problem C – Motor overheats
- Problem D – Motor bearings run hot or noisy
#1 Troubleshoot AC Motors – 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 |
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| A2: Check starter. Is overload protection device opened? |  | Replace or reset device. Does it open again when starting? |
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| A3: Is there power on all lines to motor? | | Repair starter |
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| A4: Is voltage to motor more than 10% below nameplate voltage? | | Restore proper voltage. |
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| A5: Check motor terminal connections. Are any loose or broken? | | Repair connections. |
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| A6: May be wrong motor for application. Is starting load too high? | | Install Design C or Design D motor. Install larger motor. |
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| A7: Is driven machine jammed or overloaded? | | Remove jam or overload. |
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| A8: Are misalignments, bad bearings or damaged components causing excessive friction in driven machine or power transmission system? | | Repair or replace component. |
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| 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. |
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| A10: Check stator. Are any coils open, shored or grounded? | | Repair coil or replace motor. |
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| A11: Check commutator. Are any bars or rings broken? | | Replace rotor. |
#2 Troubleshoot AC Motors – 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. |
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| B2: Is a hollow motor foundation acting as a sounding board? | | Redesign mounting. Coat foundation underside with sound dampening material. |
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| B3: Check motor mounting. Is it loose? | | Tighten. Be sure shaft is aligned. |
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| B4: Is motor mounting even and shaft properly aligned? |  | Shim feet for even mounting and align shaft. |
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| 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. |
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| B6: Is air gap nonuniform or rotor rubbing on stator? | | Recenter rotor rubbing on worn bearings or relocate pedestal bearings. |
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| B7: Listen to bearings. Are they noisy? | | Lubricate bearings. If still noisy, replace. |
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| B8: Is voltage between phases (three-phase motors) unbalanced? | | Balance voltages. |
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| B9: Is three-phase motor operating on one-phase? (Won’t start on single-phase.) | | Restore power on three-phases. |
#3 Troubleshoot AC Motors – Motor overheats
| C1: Is ambient temperature too high? |  | Reduce ambient, increase ventilation or install larger motor. |
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| C2: Is motor too small for present operating conditions? | | Install larger motor. |
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| C3: Is motor started too frequently? | | Reduce starting cycle or use larger motor. |
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| 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. |
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| 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. |
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| C6: Check input current while driving load. Is it excessive indicating an overload? |  | Go to Step C11. |
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| C7: Is the driven equipment overload? | | Reduce load or install larger motor. |
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| C8: Are misalignments, bad bearings or damaged component causing excessive friction in driven machine or power transmission system? | | Repair or replace bad components. |
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| C9: Are motor bearings dry? | | Lubricate. Does motor still draw excessive current? |
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| C10: Are damaged end bells, rubbing fan, bent shaft or rubbing rotor causing excessive internal friction? | | Repair or replace motor. |
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| C11: Are bad bearings causing excessive friction? | | Determine cause of bad bearings (See Problem D). |
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| C12: Check phase voltage. Does it vary between phases? | | Restore equal voltage on all phases. |
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| C13: Is voltage more than 10% above or 10% below nameplate? | | Restore proper voltage or install motor built for the voltage. |
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| C14: Check stator. Are any coils grounded or shorted? | | Repair coils or replace motor. |
#4 Troubleshoot AC Motors – Motor bearings run hot or noisy
| D1: Check loading. Is excessive side pressure, end loading or vibration overloading bearings? |  | Reduce overloading.* Install larger motor. |
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| D2: Is sleeve bearing motor mounted on a slant causing end thrust? | | Mount horizontally* or install ball bearing motor. |
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| D3: Is bent or misaligned shaft overloading bearings? | | Replace bent shaft or align shaft.* |
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| D4: Is loose or damaged end bell overloading shaft? | | Tighten or replace end bell.* |
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| D5: Are bearings dry? | | Lubricate.* |
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| D6: Is bearing lubricant dirty, contaminated or of wrong grade? | | Clean bearings and lubricate with proper grade* |
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| D7: Remove end bells. Are bearings misaligned, worn or damaged? | | Replace. |
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*Bearings may have been damaged. If motor still runs noisy or hot, replace bearings. |
Need more assistance troubleshooting you electric motor? Here are two great resources:
Maintenance and Troubleshooting of Electric Motors
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