Condenser Fan Motor Tripping Breaker
A 3-ton split system condenser fan motor trips the 25 A breaker after 8 to 10 minutes. Nameplate: 208/230 V, 1/4 hp, 1.8 A. Supply voltage is 228 V at the contactor; motor current is 2.1 A; the capacitor is rated 5 MFD and measures 3.2 MFD. Contactor contacts are pitted. The fan blade spins freely, and the coil is clean. The breaker is a 25 A two-pole; the unit nameplate shows minimum circuit ampacity 19 A and maximum overcurrent protection 30 A.
1. Diagnose the likely cause and explain the role of the capacitor reading.
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The capacitor is more than 30% below its rated microfarad value, which is a failed or weak run capacitor. A weak capacitor reduces the phase shift and torque of the permanent-split-capacitor motor, so the motor draws higher current and runs hotter. The measured 2.1 A versus 1.8 A nameplate current supports an overload condition, and the 8 to 10 minute trip is consistent with thermal buildup rather than an instantaneous short. Pitted contactor contacts can add voltage drop and should be replaced, but the capacitor is the first electrical defect to correct.
2. Should the breaker be replaced with a larger one? Explain.
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No. The existing 25 A breaker is already below the 30 A maximum overcurrent protection on the nameplate and above the 19 A minimum circuit ampacity, so it is a valid size. Increasing the breaker would not correct the motor overload and could allow unsafe current on the circuit conductors. The breaker is doing its job by opening on overload. Replace the capacitor and contactor, then re-measure current; if the motor still draws above nameplate or the breaker trips, investigate the motor, bearings, wiring, and breaker trip characteristics rather than upsizing protection.
3. What tests determine whether the motor must be replaced?
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After installing a correctly rated capacitor and contactor, run the motor and measure current against nameplate. Check voltage at the motor terminals under load, winding resistance, and insulation resistance to ground. Inspect the shaft for drag, listen for bearing noise, and confirm the blade is correct and balanced. If current remains above nameplate, insulation resistance is low, windings are open or shorted, or the motor overheats, replace the motor with one matching the nameplate horsepower, voltage, speed, rotation, and capacitor rating. Do not substitute a larger horsepower motor without checking the fan curve and mounting.