A PV combiner box is a crucial component in solar photovoltaic (PV) systems. It consolidates multiple strings of solar panels into one main output, enabling streamlined DC wiring, easier system maintenance, and enhanced system protection. However, even seasoned installers can make critical mistakes during installation, which may compromise system efficiency, safety, and longevity.
In this article, we’ll explore the top 5 mistakes to avoid when installing a PV combiner box, based on field experience and industry best practices. Whether you’re a solar professional or a project manager, understanding these pitfalls can help ensure your PV system runs optimally and safely.
Choosing the Wrong Combiner Box Size and Specifications
Explanation:
One of the most common errors is selecting a combiner box without properly matching it to the system’s voltage, current, and string count.
Key Considerations:
Voltage Rating: Ensure the box’s maximum voltage rating meets or exceeds the open-circuit voltage (Voc) of your solar array. A mismatch here can lead to dangerous overvoltage conditions.
Current Handling: Undersized busbars or terminals can overheat under high current loads. Always calculate the combined current of all strings and ensure the combiner box is rated accordingly.
Number of Inputs: A combiner box must support the exact number of strings in your design. If you have 12 strings, a box with only 8 input ports will not suffice.
Professional Tip: Overspecifying by 20% on current and voltage ratings provides a buffer against temperature-related changes or future expansions.
Improper String Configuration and MPPT Mismatch
Explanation:
Connecting too many or too few modules per string can result in voltage mismatches at the MPPT (Maximum Power Point Tracker) of the inverter, reducing system output.
What to Avoid:
Unequal string lengths: Avoid mixing strings with different numbers of panels in the same combiner box unless the MPPTs can handle such asymmetry.
Inconsistent orientation or tilt: Strings with varying sun exposure should ideally feed separate MPPTs, not the same combiner.
Best Practice: Use consistent string configurations for each MPPT input and verify compatibility using inverter string design tools.
Poor Wiring Practices and Loose Connections
Explanation:
Incorrect cable routing and loose terminal connections can lead to voltage drops, overheating, and even fire hazards.
Common Mistakes:
Skipping ferrules or improper crimping on multi-stranded wires
Over-tightening or under-tightening terminal screws
Using non-UV-resistant cables for outdoor installations
Neglecting proper cable bend radius and stress relief
Professional Tip: Always torque terminal screws to manufacturer specifications and use cable glands or strain relief bushings to prevent wire pull-out.
Ignoring Grounding and Surge Protection
Explanation:
Grounding and surge protection are not optional—they’re essential for preventing damage from lightning strikes and fault currents.
Issues to Watch For:
Floating grounds or unbonded ground bars
Absence of SPD (Surge Protection Device) on DC input/output terminals
Improper bonding between the combiner box and mounting structure
Best Practice: Use Class II SPD for each input group and connect to a proper earthing system (<10 ohms resistance preferred). Also ensure metal enclosures are properly bonded.
Poor Placement and Inadequate Weatherproofing
Explanation:
Combiner boxes are often installed in challenging outdoor environments. Inadequate protection from weather can result in water ingress, corrosion, and system failure.
Things to Avoid:
Installing under direct sunlight without ventilation—may cause internal temperature rise
Mounting in areas prone to flooding or without adequate IP-rated enclosures
Leaving cable entry points unsealed, allowing dust or insects to enter
Recommended Action:
Select a box with at least IP65 protection for outdoor use.
Use watertight cable glands.
Install in a shaded area or use sun shields.
Professional Tip: If placed on a rooftop, elevate the combiner box to avoid pooling water and ensure adequate airflow.
Conclusion: Install with Precision, Operate with Confidence
Avoiding these common mistakes during PV combiner box installation ensures long-term performance, safety, and reliability of your solar system. Proper component selection, accurate string design, and professional installation practices are all essential.
At Derlicn Electric, we offer a full range of DC combiner boxes, string monitoring combiner boxes, and customized solutions tailored to your PV project needs. Let our engineering team assist you in optimizing your next installation.
👉 Browse our combiner box selection or contact our technical team for one-on-one support today!
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