ServiceNomad RV · Knowledge
RV Breaker Trips When AC Starts
A circuit breaker that trips specifically when you turn on the RV air conditioner is one of the most common electrical complaints. The AC unit draws high startup current (locked rotor amps) for a brief moment, and if this surge exceeds the breaker's capacity, the breaker trips to protect the wiring from overheating. Understanding why AC startup causes breaker trips helps you determine whether the issue is the breaker, the AC unit, or the power supply.
Understanding AC Startup Surge
Compressor motors draw 3-5 times their running current during the first second of startup. This surge—called 'locked rotor amps' (LRA)—happens because the compressor starts from a dead stop and must overcome internal mechanical resistance and build up refrigerant pressure. For a typical 13,500 BTU RV AC, running current is about 12-15 amps, but LRA can be 60-80 amps or higher. Circuit breakers are designed to handle brief surges, but if the surge is too high or lasts too long (due to compressor problems or low voltage), the breaker's thermal or magnetic trip mechanism activates. A 20-amp breaker may tolerate 40 amps for a few milliseconds, but not 80 amps or sustained high current.
Low Voltage and Breaker Sensitivity
Low incoming voltage makes everything worse. When voltage drops below 115V (common at crowded campgrounds), the AC motor demands more amps to generate the same mechanical power. This increases both the startup surge and running current, making breaker trips more likely. A breaker that holds fine at 120V may trip instantly at 108V. Monitoring voltage with a portable multimeter or installing an EMS (Electrical Management System) helps you know when voltage is dangerously low. If voltage is consistently below 115V, you may need to use a generator, move to a different site, or avoid running the AC during peak hours when campground voltage sags.
Failed Start Capacitor or Hard Start Kit
The start capacitor provides an electrical boost to help the compressor overcome initial resistance during startup. If the capacitor has failed or lost capacitance, the compressor tries to start but draws excessive locked rotor current for too long, tripping the breaker. Installing a hard start kit (or replacing a failed one) dramatically reduces the startup surge and often solves chronic breaker trips. A technician can test the start capacitor with a multimeter in capacitance mode. If readings are far below the rated microfarads (stamped on the capacitor), replacement is needed. Many techs also recommend installing a Micro-Air EasyStart or similar device, which reduces startup surge by 50-70%.
Breaker Wear and Heat Damage
Circuit breakers themselves can weaken over time, especially if they've been subjected to repeated trips or high heat. The internal bi-metal strip or magnetic coil may become more sensitive and trip at currents lower than the rated amperage. This is especially common in RVs where breakers are often located in hot compartments or near heat-producing components. If you've replaced the AC components and ensured good voltage but the breaker still trips, consider having the breaker tested or replaced. Use only the correct amperage breaker specified for the circuit—never 'upgrade' to a higher-amp breaker without verifying the wire gauge can handle it.
⚠️ Safety Notes
- Never replace a breaker with a higher amperage rating to 'fix' tripping—this removes overcurrent protection and creates a fire hazard.
- If a breaker trips hot (you can feel heat on the breaker handle), let it cool completely before resetting—repeated hot trips indicate a serious problem.
💡 Prevention Tips
- Install a soft-start device on the AC to reduce startup surge and protect the breaker.
- Monitor campground voltage and avoid running AC when voltage drops below 115V.
- Have AC capacitors tested annually—proactive replacement prevents sudden failures and breaker trips.
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