1. DC Primary Circuit Path (PV+ → Fuse → Combiner → Output)
Read the diagram left to right (or bottom to top):
- Input: N strings, each PV+ and PV- passing through its own gPV fuse (two-pole protection);
- Busbar: the outputs of all fuses combine onto the PV+/PV- copper busbars;
- main breaker: DC load-break switch / DC circuit breaker (for isolation, rated voltage ≥ system voltage);
- Output: routed through a waterproof cable gland to the DC side of the inverter.
2. Polarity and Color Coding (Red Positive, Black Negative)
| Polarity | Conductor / Busbar Color | Terminal Marking |
|---|---|---|
| PV+ | Red (or brown) | DC+ / PV+ |
| PV− | Black (or blue) | DC− / PV− |
| PE | Yellow-green | PE |
DC polarityReversed connection burns the fuse at best, destroys equipment at worst— check the polarity markings on the diagram first, then verify with a multimeter before energizing.
3. Surge Protective Device (SPD) Wiring (ground discharge)
- Wiring method: Connect one module (or an integrated 3-terminal unit) between PV+ and PE, and another between PV− and PE; mount the SPD at the main switchdownstream stage, close to the output end;
- Backup protection: install a DC-rated backup fuse ahead of the SPD (size per the SPD datasheet);
- Grounding: connect the SPD PE terminal to the cabinet PE bar with theshortest straight run; grounding resistance ≤ 4Ω;
- Remote signaling: wire the degradation signaling contact into the monitoring circuit; verify NO/NC against the drawing.
4. Monitoring Module Wiring (secondary circuit)
Monitoring module wiring falls into four groups: ① each string'sHall sensor / shuntsamples string current; ② busbar voltage sampling; ③ RS485 communication(A/B twisted pair with shielded ground, to the inverter / monitoring system); ④ auxiliary power(typically DC 24V or AC 220V). When reading the drawing, noteseparate routing for power and signal cablesand single-end grounding of the 485 shield — cable specs and shielding requirements are called out on the drawing.
5. Five Wiring Practice Points (construction acceptance)
① Torque: tighten fuse holders and busbar bolts to the torque table and mark with a line; ② Crimp: match cold-pressed cable lugs to conductor size; tinning before crimping is prohibited; ③ Firestop sealing: seal cable entry holes with both waterproof firestop putty and firestop sealant; ④ Wire sequence: tag each input per the drawing number (PV1+ / PV1− …) and match it one-to-one with the monitoring module channel; ⑤ Re-check: before energizing, verify polarity with a multimeter and insulation resistance ≥ 1MΩ (1000V megohmmeter).
FAQ FAQ
Do both the positive and negative poles of a combiner box need fuses?
We recommend fuses on both poles. DC fault current has no natural zero crossing, so two-pole fusing improves breaking reliability (follow the design drawing for the specific configuration).
Should the SPD go before or after the main switch?
Typically installed atthe downstream side (near the output), per the drawing; either way, the run from the SPD to the PE bar must be as short as possible.
What cable should be used for the RS-485 communication line?
Shielded twisted pair (e.g., RVSP 2×0.75), with the shieldgrounded at one end only, routed in a separate tray from power cables.
Does the solar combiner box require an insulation test?
Yes. Before energizing, use a 1000V megohmmeter to measureDC circuit-to-ground insulation ≥ 1MΩ. Do not perform the test in rainy weather.
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