What happens if a DC breaker is undersized in a solar system?

Overheating Risks

An undersized DC breaker in a solar system can lead to excessive current flowing through the breaker, causing it to overheat. This is particularly true for high-current PV systems, where a mismatch between the breaker and the system’s capacity can result in rapid overheating. For example, a 30-amp DC breaker may be insufficient for a 3.0 kW solar array with 48V DC output, as it would only be able to handle approximately 62.5 amps of current, which is below the array’s maximum current draw.

System Instability and Voltage Drop

An undersized DC breaker can also cause system instability and voltage drop. As the breaker struggles to handle the high current, it can create voltage spikes and drops within the system, affecting the performance of the inverter, charge controller, and other equipment. This can lead to reduced efficiency, increased wear and tear on equipment, and even complete system failure.

Best Practices for DC Breaker Sizing

To avoid these risks, it’s essential to properly size DC breakers according to the system’s requirements. This involves calculating the maximum current draw of the solar array, accounting for factors such as the array’s size, voltage, and inverter efficiency. A general rule of thumb is to size the breaker to handle at least 125% of the maximum current draw of the array, with a minimum of 20-amp increments for larger systems.