What Is The Difference Between 4mm And 6mm Solar Cable

In solar power generation systems, the choice of cables is critical to the performance, safety, and long-term reliability of the system. 4mm and 6mm solar cables are two common specifications that differ significantly in several aspects. Understanding these differences can help solar system installers and investors make more informed decisions.

 

What is a solar cable, and why is it important?

 

Solar cables are a type of wire and cable specially designed for solar photovoltaic systems, consisting of conductors, insulation layers, sheaths, and other parts. Compared with ordinary cables, they have extremely strong weather resistance and can maintain stable performance in extreme temperature environments ranging from -40°C to 90°C; they also have excellent resistance to UV rays, ozone, and chemical corrosion, and can be exposed to harsh outdoor environments for a long time without aging. In addition, solar cables also have good flame retardancy and mechanical strength, and can withstand external forces such as stretching and bending during installation and use.

 

Understanding solar cable types and uses

Solar cables can be divided into many types according to insulation materials, conductor materials and uses.

According to insulation materials, there are cross-linked polyethylene (XLPE) and polyvinyl chloride (PVC) insulated cables. The former has better weather resistance and is suitable for long-term outdoor exposure scenes. The latter has low cost but slightly poor weather resistance and is suitable for short-distance connections with low environmental requirements.

According to conductor materials, there are copper core and aluminum core cables. Copper core has good conductivity and long life, and is suitable for high-requirement long-distance scenes. Aluminum core has low cost and light weight, and is suitable for cost-sensitive short-distance scenes; according to use, there are photovoltaic module interconnection, DC and AC cables, which are used for module connection, DC to inverter transmission, AC to grid or load transmission, respectively.

 

 

The role of cable size in solar installations

In solar installations, cable size is not a simple physical parameter, but a core factor that directly affects system performance, safety and economy. Cables of different specifications play an irreplaceable role in current transmission, loss control, installation and adaptation. ​

 

Cable size determines current carrying capacity. The larger the cross-sectional area of the conductor (such as 6mm cable), the higher the current intensity that can be carried. In large photovoltaic arrays, a large number of components in series or parallel will generate high current. At this time, if a cable with too small size (such as 4mm) is selected, the conductor may heat up due to overload, accelerate the aging of the insulation layer, and even cause a short circuit fire. The adapted large-size cable can stably divert the current and ensure the safe operation of the system during peak power generation. ​

 

Size directly affects voltage drop and energy loss. According to Ohm's law, under the same material, the resistance of thin cable (4mm) is greater than that of thick cable (6mm). In long-distance transmission scenarios (such as the junction box to inverter line in large power stations), thin cables will produce obvious voltage drop due to excessive resistance, resulting in insufficient effective voltage obtained by the terminal equipment, reducing power generation efficiency. Larger cables such as 6mm can reduce power loss, especially in high-power systems, and the long-term accumulated energy-saving benefits are very significant. ​

 

 

Why choosing the correct solar cable matters

Appropriate cables can reduce power transmission losses. The electricity generated by solar panels needs to be transmitted to inverters, power grids or energy storage devices via cables. If the cable specifications are insufficient (such as misusing thin cables in high-power scenarios), the voltage drop will increase due to excessive resistance, directly reducing power generation efficiency.

 

 

How do 4mm and 6mm cables differ in solar systems?

Comparison of 4mm and 6mm solar cables

Cross-sectional area​
●The cross-sectional area of 4mm solar cable is 4 square millimeters
●The cross-sectional area of 6mm solar cable is 6 square millimeters, which is significantly larger than 4mm cable. ​

Current carrying capacity​
●4mm cable can usually carry 25-30 amperes of current
●6mm cable can carry 35-45 amperes of current, and has a stronger current carrying capacity. ​

Voltage drop​
●4mm cable has a large resistance, and the voltage drop is obvious when the transmission distance exceeds 50 meters
●6mm cable has a small resistance, and the voltage drop is still relatively stable in long-distance transmission over 100 meters. ​

Cable resistance​
●Under the same material, the resistance of 4mm cable is relatively large
●6mm cable has a smaller resistance due to its large cross-sectional area. ​

Usage scenario​
●4mm is suitable for low-power and short-line scenarios such as small household rooftop photovoltaics
●6mm is suitable for high-power and long-distance transmission scenarios such as large solar power stations and commercial photovoltaic projects. ​

 

*This understanding of the parameters enables system designers and installers to properly assess if the project necessitates the use of 4mm or 6mm cables in accordance with the requirements of the solar installation.

 

 

Impact of cable size on voltage drop

Cable size (cross-sectional area) is the core factor affecting voltage drop. In solar systems, the performance of 4mm and 6mm cables is significantly different: ​

 

4mm cables have a small cross-sectional area and a large conductor resistance. According to Ohm's law, the greater the resistance, the more obvious the voltage drop is at the same current and transmission distance. For example, when the transmission distance exceeds 50 meters, the voltage drop of 4mm cables will increase significantly, which may cause insufficient voltage at the end device and affect system efficiency. ​

 

6mm cables have a larger cross-sectional area and a smaller conductor resistance, so the voltage drop control is better. Even in long-distance transmission of more than 100 meters, the voltage drop of 6mm cables can still be kept at a low level, which can stably ensure the power supply of end devices and reduce efficiency losses caused by voltage fluctuations.

 

 

Difference in current carrying capacity between 4mm and 6mm solar cables

4mm cable: Due to its smaller cross-sectional area, the current carrying capacity is usually 25-30 amps. Suitable for low-power scenarios, such as small home photovoltaic systems, and can meet low current transmission needs.

6mm cable: With a larger cross-sectional area, the current carrying capacity can reach 35-45 amps, which is significantly higher than 4mm cable. Suitable for high-power scenarios, such as large power stations and commercial photovoltaic projects, and can handle high current transmission.

 

 

What factors should you consider when choosing the right cable?

Evaluate the temperature rating of the cable

Core determining factors: Determined by the insulation/sheath material (such as PVC resistant to 70-90℃, XLPE resistant to 90-125℃, silicone rubber resistant to more than 180℃) and the conductor material (copper is better than aluminum), reflecting the upper limit of the maximum temperature for long-term stable operation.

 

Impact on performance: Overheating will accelerate insulation aging and cause short circuits. High temperature environments need to match high temperature resistance levels (such as outdoor selection of more than 125℃); Increased ambient temperature will reduce the actual current carrying capacity (such as the current carrying capacity at 40℃ is about 15% lower than that at 25℃); Low temperature may cause cable embrittlement (such as PVC is easy to break below -15℃).

 

Evaluate cable length and its impact

Core impact: Line loss (voltage loss): Length is proportional to resistance. The greater the resistance, the higher the voltage loss (ΔU=IR). For example, at a distance of 100 meters, the line loss of 4mm² copper cable is about 40% higher than that of 6mm², which may cause insufficient power supply to the equipment; ​

Current carrying capacity correction: Long-distance (>100 meters) cables have poor heat dissipation, and the current carrying capacity needs to be reduced by 10%-20%; ​

Installation restrictions: For cables that are too long, the wiring space, bending radius and connector reliability must be considered (too many connectors can easily increase the number of fault points). ​

Solutions: For long distances, thicker wire diameters (such as 6mm² and above) are preferred, and the voltage loss is controlled within 5%.