Wiring process for photovoltaic combiner boxes

A PV combiner box wires multiple solar panel strings through individual fuses or breakers to a common busbar, with proper grounding and surge protection, before connecting to the inverter.

Overview

A photovoltaic combiner box consolidates the outputs of multiple solar panel strings into a single DC output for the inverter, simplifying wiring, enhancing safety, and providing overcurrent and surge protection . Each string connects to the combiner box via dedicated input terminals, typically through DC fuses or miniature circuit breakers, which isolate individual strings in case of faults .

Wiring Steps

1. String Connections
   • Connect the positive (+) conductor from each solar string to the line side of its respective fuse or breaker.
   • Connect the load side of the fuse or breaker to the positive busbar inside the combiner box.
   • Connect all negative (-) conductors directly to the negative busbar without fusing, following NEC 690.9(B) guidelines .
2. Busbar and Output Wiring
   • The positive and negative busbars combine the strings into a single output.
   • From the busbars, run appropriately sized conductors to the inverter input, ensuring voltage and current ratings are not exceeded .
3. Grounding and Bonding
   • Connect the equipment grounding conductor (EGC) to the combiner box metal enclosure.
   • Install bonding jumpers to maintain an equipotential plane, ensuring fault currents have a safe path to ground .
   • SPD (surge protection devices) modules should be connected between positive/negative busbars and ground to protect against transient overvoltages .
4. Wire Sizing and Routing
   • Use conductors sized according to the ampacity of each string and the total combined current.
   • Maintain proper separation of positive and negative wires, avoid sharp bends, and secure cables to prevent mechanical stress .
5. Final Checks
   • Verify all connections are tight and correctly oriented.
   • Ensure fuses or breakers are rated for the string current.
   • Confirm grounding continuity and SPD connections.
   • Follow the wiring diagram for your specific combiner box model to ensure compliance with IEC 60364-7-712 and NEC Article 690 .

Key Considerations

• Install the combiner box in a well-ventilated, weather-protected location with at least IP65/66 protection.
• Each string should be individually fused to isolate faults without affecting the entire array.
• Proper wiring reduces the risk of short circuits, ground faults, and overcurrent damage, ensuring long-term reliability . By following this wiring method, a PV combiner box safely integrates multiple solar strings, provides overcurrent and surge protection, and ensures efficient, maintainable operation of the photovoltaic system.