2.5mm² vs 4mm² vs 6mm²: Which Solar Cable Size Is Best?

Choosing the correct cable size is one of the most important decisions in any solar installation. At the heart of every system lies the wiring, and selecting the right cross-section affects safety, performance, and long-term efficiency. Whether you’re designing a home rooftop array or a multi-MW project, understanding the differences between 2.5mm² photovoltaic cable, 4mm², and 6mm² is essential.

The cable size influences voltage drop, current-carrying capacity, heat resistance, and overall reliability. When sourced from a solar-specific manufacturer that maintains standardized quality control, your cable selection becomes even more dependable.

Why Cable Size Matters in Solar Systems

A photovoltaic system generates direct current (DC), and DC cabling can be sensitive to resistance and heating. Undersized cables may lead to:

Excessive voltage drop

Reduced energy yield

Higher operating temperatures

Potential safety risks during long-term operation

Oversized cables, on the other hand, increase cost and may complicate routing. The goal is to choose a size that maintains balance: safe, efficient, and proportionate to your system’s needs.

Understanding the Three Common Sizes

1. 2.5mm² Photovoltaic Cable

This is the smallest of the three popular PV cable sizes. It is designed for low-current, short-distance applications where energy loss is minimal. Key characteristics include:

Suitable for low-power or compact systems

Ideal for short string connections

Lower material cost compared to larger sizes

However, because resistance increases as cross-section decreases, 2.5mm² photovoltaic cable is typically recommended only when currents are modest and cable runs are relatively short.

2. 4mm² Solar Cable

This size is often considered the industry’s “standard” for many residential and small commercial systems. Advantages include:

Better current-carrying capability

Reduced voltage drop over medium distances

Improved heat resistance

Suitable for most 1–2 string connections in home solar systems

It is a strong middle-ground option when installers need improved performance without significant cost increases.

3. 6mm² Solar Cable

For demanding installations, 6mm² offers enhanced performance:

Excellent for long cable runs

Lower resistance and minimal voltage loss

Handles higher currents

Better suited for larger rooftop arrays or ground-mount PV systems

If you expect the system to operate near maximum current for extended periods, or if the array layout demands long runs between modules and combiner points, 6mm² becomes the safer, more efficient choice.

Voltage Drop: The Deciding Factor

Voltage drop is often the determining reason to choose 2.5, 4, or 6mm² cable. The longer the distance or the higher the current, the greater the potential drop. Excessive voltage drop reduces system output and can affect inverter performance.

As a rule of thumb:

For short distances (<10 m) and low-power modules → 2.5mm² may suffice

For moderate distances (10–25 m) → 4mm² is typically recommended

For longer distances (>25 m) or high-current flows → 6mm² ensures stability

Keeping voltage drop below 3% is considered ideal for most solar installations.

System Current and Cable Heating

Cable heating occurs when the current exceeds or approaches the rated ampacity of the cable. Larger cross-sections dissipate heat more easily.

A 2.5mm² cable is acceptable for lower currents

A 4mm² cable handles mid-range loads safely

A 6mm² cable prevents overheating in larger arrays

Temperature rating also matters. Quality PV cables typically carry ratings like 90°C continuous or 120°C short-circuit endurance. When sourced through stable production processes, these thermal properties remain consistent across batches.

Installation Environment Matters

Solar cable performance is directly influenced by installation conditions:

On rooftops exposed to high temperatures

In conduits with limited heat dissipation

In ground-mount arrays in full sun

In areas with harsh environmental cycles

Dust, UV radiation, mechanical abrasion, and temperature fluctuations can all stress the cable. In harsher conditions, selecting the larger cross-section (4mm² or 6mm²) adds an extra layer of protection and longevity.

Safety Considerations

Safety is a core reason why cable sizing should never be overlooked. A cable that is too small for its load may:

Overheat over time

Accelerate insulation aging

Increase fire risk

Trigger inverter shutdowns

Cause repeated power losses

Oversizing improves safety margins but should still be aligned with system design and connector compatibility.

Which Size Should You Choose?

Choose 2.5mm² if:

Cable runs are short

Currents are low

The system is compact

Cost optimization is a priority

Choose 4mm² if:

You need a reliable standard for most residential systems

Voltage drop must be controlled over medium distances

You want performance without large cost increases

Choose 6mm² if:

The installation involves long runs or high currents

The environment is harsh or temperatures are high

You want enhanced safety and long-term durability

The PV system approaches utility-scale or large commercial design

Conclusion

Selecting the right solar cable size is not simply a matter of cost — it directly affects performance, energy yield, and system safety. While 2.5mm² photovoltaic cable works well in compact systems, 4mm² provides balance for mainstream installations, and 6mm² supports longer or heavier-load solar arrays.

When choosing, always evaluate current, distance, voltage drop, and environmental factors. Sourcing from a professional solar-focused manufacturer with consistent production quality ensures that whichever size you select, your system will operate efficiently and reliably for years.

The right cable size — whether 2.5, 4, or 6mm² — defines the foundation of a secure and high-performing solar installation, starting with a dependable 2.5mm² photovoltaic cable at the core of every comparison.

References

Bello, M., Parlevliet, D., & Whale, J. (2020). Analysis of voltage drop and cable sizing for low-voltage photovoltaic systems. Renewable Energy, 146, 2514–2526.