Five-Ton Condenser on 10 AWG Wire and a 50 A Breaker
A contractor installs a 5-ton split system. The condenser nameplate lists minimum circuit ampacity 32.5 A and maximum overcurrent protection 40 A. The existing circuit is 10 AWG NM-B on a 50 A breaker with a 60 A non-fused disconnect. The run is 55 ft from the panel to the disconnect. The installer reuses the existing circuit and sets the thermostat to 'fan on' continuously because the homeowner wants air circulation. On startup, the breaker trips after about 10 minutes. The contractor says the breaker is bad and wants to replace it with a 60 A breaker. The homeowner asks whether that is safe and code-compliant.
1. Evaluate the conductor, breaker, and disconnect against the nameplate and NEC requirements.
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The nameplate MCA is 32.5 A and MOP is 40 A. The branch-circuit conductors must have an ampacity of at least 32.5 A, and the overcurrent device must not exceed 40 A. 10 AWG NM-B has a 60°C ampacity of 30 A, so it is undersized. The 50 A breaker is already above the MOP, and a 60 A breaker would be worse: it would not protect the equipment per the nameplate and could overheat the 10 AWG conductors.
The 60 A non-fused disconnect may be acceptable only if its rating is adequate for the circuit, but it does not fix the conductor or breaker. Correct with 8 AWG NM-B, 40 A at 60°C, on a 40 A breaker, or 8 AWG THHN or THWN in conduit where 75°C terminations allow 50 A, still protected at 40 A. Verify terminations and voltage drop for the 55 ft run.
2. What are likely causes of the trip, and what should be checked before changing the breaker?
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The 10-minute trip is likely a real overload, not a bad breaker. The compressor RLA is 26.4 A; add the condenser fan and crankcase heater, and the running current is near or above the 30 A ampacity of 10 AWG. High head pressure from low airflow, overcharge, a failing condenser fan, a weak capacitor, or a bad contactor can also raise current.
The contractor should measure supply voltage, compressor amps against nameplate RLA, condenser fan amps, pressures, superheat and subcooling, and capacitor microfarads. The 55 ft run also needs a voltage-drop check. Replacing the 50 A breaker with a 60 A breaker masks the problem and violates the nameplate MOP. Do not upsize the breaker.
3. What corrections and startup checks should be documented?
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Correct the circuit first: install conductors with at least 32.5 A ampacity, a 40 A overcurrent device, proper terminations torqued at the panel and disconnect, and a disconnect within sight of the equipment. Then start the system and document voltage, compressor and fan amps, pressures, superheat and subcooling, condenser entering and leaving air temperature, and temperature split.
Check that the continuous fan setting does not exceed the duct static or cause coil bypass; continuous fan can also raise indoor humidity. If the system still trips after the circuit is corrected, diagnose the refrigeration or mechanical cause. Document all readings and the corrected nameplate compliance.