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Circuit Breaker Sizing Chart for Solar PV Installations 2025
Choosing the right circuit breaker for a solar PV system is critical. A circuit breaker protects the system from overloads and short circuits, preventing fires and damage to panels, inverters, and wiring. Using a breaker that is too small can cause it to trip constantly; one that is too large won’t trip when needed, risking danger. Below is a simple guide to sizing circuit breakers for solar PV installations in 2025, with clear advice for different system parts.
Understanding Solar PV System Parts
A solar PV system has several key parts, each needing its own circuit breaker.
Solar panels are grouped into strings, and each string needs a breaker to protect the wiring between the panels and the inverter. The inverter, which converts DC power from the panels to AC power for home use, requires breakers on both its input (DC) and output (AC) sides. If the system includes battery storage for excess power, a breaker is needed to protect the battery and its wiring from overcurrent. Finally, the main electrical panel, where the solar system connects to the home’s main power, has a breaker that controls the flow of solar power into the home. Each part has different current needs, so each breaker must be sized accordingly.
Key Terms for Sizing
Before diving into sizing, learn these simple terms.
Current, measured in amps, is the flow of electricity. All solar parts have a “maximum current” rating, and breakers must be able to handle this. Voltage, measured in volts, is the force pushing the electricity; higher voltage means lower current for the same amount of power. Continuous current is the steady flow during normal use, and breakers must be sized for 125% of this (a safety rule to prevent overheating). Short circuit current is the sudden, high current from a short circuit, and breakers must trip quickly to stop this.
Sizing Circuit Breakers for Solar Panels
Solar panels are wired in strings, and the breaker for a string must handle the maximum current from the panels.
For example, if you have 4 panels per string, each with 300 watts, the maximum current from the string is around 8.5 amps. To find the right breaker size, calculate 125% of this maximum current (8.5 amps x 1.25 = 10.625 amps), so a 10-amp breaker works. If the string has 6 panels of 300 watts each, the maximum current is still 8.5 amps (since adding more panels in a string increases voltage, not current), so a 10-amp breaker is still sufficient.
For 400-watt panels, a string of 4 panels has a maximum current of about 11.0 amps. 125% of 11.0 amps is 13.75 amps, so a 15-amp breaker is needed. A string of 6 panels with 400 watts each also has a maximum current of 11.0 amps, so a 15-amp breaker is correct here too.
For 500-watt panels, a string of 4 panels has a maximum current of around 14.0 amps. 125% of 14.0 amps is 17.5 amps, so a 20-amp breaker is required. The same applies to a string of 6 panels with 500 watts each, which also has a maximum current of 14.0 amps, needing a 20-amp breaker.
Sizing Circuit Breakers for Inverters
Inverters convert DC power from panels to AC power, and they need breakers on both their input (DC) and output (AC) sides.
DC Input Side
For a 3kW inverter, the maximum DC current is about 22 amps. 125% of 22 amps is 27.5 amps, so a 30-amp breaker is needed. A 5kW inverter has a maximum DC current of around 35 amps. 125% of 35 amps is 43.75 amps, so a 45-amp breaker works.
A 7.6kW inverter has a maximum DC current of about 50 amps. 125% of 50 amps is 62.5 amps, so a 60-amp breaker is required. For a 10kW inverter, the maximum DC current is around 65 amps. 125% of 65 amps is 81.25 amps, so an 80-amp breaker is suitable.
AC Output Side
On the AC side, a 3kW inverter outputs a maximum current of about 13 amps. 125% of 13 amps is 16.25 amps, so a 20-amp breaker is needed. A 5kW inverter has an AC output current of around 21 amps. 125% of 21 amps is 26.25 amps, so a 30-amp breaker is correct.
A 7.6kW inverter outputs a maximum AC current of about 32 amps. 125% of 32 amps is 40 amps, so a 40-amp breaker works. For a 10kW inverter, the maximum AC output current is around 42 amps. 125% of 42 amps is 52.5 amps, so a 50-amp breaker is suitable.
Sizing Circuit Breakers for Battery Storage
Batteries store power and release it when needed, and their breaker must handle the current during charging and discharging.
A 5kWh battery has a maximum charge/discharge current of around 40 amps. 125% of 40 amps is 50 amps, so a 50-amp breaker is needed. For a 10kWh battery, the maximum current is about 60 amps. 125% of 60 amps is 75 amps, so a 75-amp breaker works.
A 15kWh battery has a maximum current of around 80 amps. 125% of 80 amps is 100 amps, so a 100-amp breaker is required. For a 20kWh battery, the maximum current is about 100 amps. 125% of 100 amps is 125 amps, so a 125-amp breaker is suitable.
Sizing Circuit Breakers for Main Panel Connection
The breaker in the home’s main panel controls the flow of solar power into the home.
For a total solar system size of 3kW, the maximum AC current entering the home is around 13 amps. 125% of 13 amps is 16.25 amps, so a 20-amp breaker is needed. A 5kW system has a maximum AC current of about 21 amps. 125% of 21 amps is 26.25 amps, so a 30-amp breaker works.
A 10kW system outputs a maximum AC current of around 42 amps. 125% of 42 amps is 52.5 amps, so a 50-amp breaker is suitable. For a 15kW system, the maximum current is about 63 amps. 125% of 63 amps is 78.75 amps, so an 80-amp breaker is needed. A 20kW system has a maximum current of around 84 amps, and 125% of 84 amps is 105 amps, so a 100-amp breaker works.
Tips for Sizing Breakers in 2025
Use 2025 standards, as new solar panels and inverters in 2025 are more efficient but may have higher current peaks. Always check the manufacturer’s 2025 specifications for accurate maximum current ratings.
Account for temperature: In hot areas, where average temperatures are over 90°F (32°C), wires and breakers can overheat. Increase the breaker size by 10% in these locations to compensate.
Avoid mixing brands: Use breakers from the same brand as your inverter or panels. Mismatched parts can cause tripping or failure, as different brands may have slightly different current handling capabilities.
Check local codes: Some areas have specific rules. For example, California requires breakers to be labeled for solar use, and other regions may have similar requirements to ensure safety and compatibility.
FAQ
What happens if the breaker is too small?
It will trip often, shutting down the solar system. This reduces energy production and can damage the breaker over time, as frequent tripping wears out the internal components.
Can I use a larger breaker than recommended?
No. A larger breaker won’t trip during overloads, allowing too much current to flow through wires and equipment. This can cause overheating, fires, or permanent damage to panels, inverters, or wiring.
Do I need a special breaker for solar systems?
Yes. Solar breakers are designed to handle DC power, which is more dangerous than AC because it doesn’t alternate, making it harder to interrupt. They also have higher durability for outdoor use, as many solar system breakers are installed in outdoor enclosures.
How often should I check the breakers?
Inspect them every 6 months. Look for signs of overheating, such as burn marks, melted plastic, or a strong, acrid smell. Also, check for corrosion, especially in humid or coastal areas, as corrosion can prevent the breaker from tripping properly.
Can I install the breaker myself?
It’s better to hire a licensed electrician. Solar systems involve high voltages (both DC and AC), and incorrect installation can be deadly. Electricians have the training to size and install breakers correctly, ensuring compliance with local codes and safety standards.