How to Size and Select a PV Combiner Box for Your Solar Project

Choosing the correct PV combiner box is essential to the safety, efficiency, and performance of your solar system. With various models available in the market, understanding your project’s needs helps avoid under- or over-specification.

Determine the Number of Strings

The number of DC strings you intend to combine is the primary factor in sizing your combiner box. Each string requires a separate input circuit with a fuse or breaker. For example, a 12-string system will require a combiner box with at least 12 fuse holders.

Voltage and Current Ratings

Ensure the combiner box can handle the open circuit voltage (Voc) and short-circuit current (Isc) of your PV panels. Safety margins are typically included, so choose boxes rated at least 10–20% above system max ratings.

Surge Protection and Disconnects

For outdoor or lightning-prone environments, include built-in surge protection. Some boxes also integrate disconnect switches for easier field maintenance.

Environmental and Certification Requirements

Look for NEMA 4X or IP65-rated enclosures to ensure protection from dust, rain, and UV. UL1741 or IEC compliance ensures the unit meets global safety standards.

Conclusion

Properly sizing and selecting a PV combiner box will maximize system performance while ensuring safety and compliance. Work with a reputable supplier who can provide technical guidance and customization if needed.