4mm² vs 6mm² Solar Cable: Which Size Should You Use?

Choosing between 4mm² and 6mm² solar cable is one of the most common decisions when designing a photovoltaic system. Both cable sizes are widely used for connecting solar panels, combiner boxes, inverters, and other DC components. However, the correct size depends on more than the rated power of the solar panels.

Current, cable length, system voltage, allowable voltage drop, installation temperature, and local electrical requirements must all be considered. Selecting a cable that is too small can increase power loss and cable temperature, while using an unnecessarily large cable can increase project cost and make installation more difficult.

What Do 4mm² and 6mm² Mean?

The values 4mm² and 6mm² refer to the nominal cross-sectional area of the cable conductor. They do not refer to the outside diameter of the complete cable.

• 4mm² solar cable: The conductor has a nominal cross-sectional area of 4 square millimeters.
• 6mm² solar cable: The conductor has a nominal cross-sectional area of 6 square millimeters.

A larger conductor has lower electrical resistance. Therefore, a 6mm² solar cable normally produces less voltage drop and less heat than a 4mm² cable carrying the same current over the same distance.

Both sizes are commonly manufactured with flexible tinned copper conductors, cross-linked insulation, and UV-resistant outer sheaths. Depending on the target market, certified solar cables may comply with standards such as EN 50618 or IEC 62930.

4mm² vs 6mm² Solar Cable Comparison

When Should You Use 4mm² Solar Cable?

A 4mm² solar cable is widely used in residential, commercial, and small utility-scale photovoltaic systems. It is often the most economical choice when the cable run is relatively short and the circuit current is within the cable’s permitted capacity.

4mm² cable may be suitable when:

• The cable distance between the solar panels and inverter is short or moderate.
• The PV string current is relatively low.
• The calculated voltage drop is within the project limit.
• The cable is installed with adequate ventilation.
• Ambient temperature and rooftop temperature are not unusually high.
• The connector, junction box, and cable gland are designed for 4mm² cable.

For many standard rooftop PV strings, 4mm² solar cable provides a good balance between electrical performance, flexibility, ease of installation, and cost.

However, cable size should never be selected only because 4mm² is commonly used. The actual current and cable length must still be calculated for each installation.

When Should You Use 6mm² Solar Cable?

A 6mm² solar cable is preferred when the installation requires lower resistance, lower voltage drop, or a greater current-carrying margin.

6mm² cable may be the better choice when:

• The distance from the PV array to the inverter is long.
• The solar modules have a relatively high operating current or short-circuit current.
• Several conductors are bundled together.
• The cable is installed inside conduit, trunking, or an enclosed space.
• The rooftop or ambient temperature is high.
• The project has a strict voltage-drop requirement.
• Future system expansion may increase circuit current.
• The installer wants to reduce long-term resistive energy losses.

Although 6mm² cable costs more than 4mm² cable, the additional cost may be justified when it reduces energy loss over the operating life of the solar system.

How Cable Length Affects Solar Cable Size

Cable length is one of the most important factors in selecting between 4mm² and 6mm² solar cable. The longer the cable, the greater its total resistance and voltage drop.

When calculating a two-conductor DC circuit, remember that current travels through both the positive and negative cables. Therefore, a 30-meter one-way distance normally represents approximately 60 meters of total conductor length for the voltage-drop calculation.

A simplified voltage-drop formula is:

Actual resistance increases as the conductor temperature rises. For this reason, calculations based only on resistance at 20°C may underestimate voltage drop under hot operating conditions.

Voltage Drop Example: 4mm² vs 6mm²

Consider a PV string with the following conditions:

• Operating current: 15A
• One-way cable distance: 30 meters
• Total positive and negative conductor length: 60 meters
• Approximate copper conductor resistance at 20°C:
  • 4mm²: approximately 4.61 Ω/km
  • 6mm²: approximately 3.08 Ω/km

Using 4mm² Solar Cable

Voltage drop:

15A × 4.61 Ω/km × 0.06km = approximately 4.15V

Power loss:

15A × 4.15V = approximately 62.3W

Using 6mm² Solar Cable

Voltage drop:

15A × 3.08 Ω/km × 0.06km = approximately 2.77V

Power loss:

15A × 2.77V = approximately 41.6W

In this example, changing from 4mm² to 6mm² reduces cable power loss by approximately 20.7W while the circuit is operating at 15A. The long-term financial benefit depends on operating hours, solar irradiance, electricity value, and the additional cable cost.

This is a simplified example. Final cable selection should also consider operating temperature, grouping, conduit installation, connector ratings, protection devices, and applicable electrical codes.

Current-Carrying Capacity Is Not a Fixed Number

It is common to ask how many amps a 4mm² or 6mm² solar cable can carry. However, there is no single current rating that applies to every installation.

The permitted current depends on:

• Conductor material and construction
• Insulation temperature rating
• Ambient temperature
• Installation in free air, conduit, trunking, or underground
• The number of cables installed together
• Ventilation and heat dissipation
• Required cable life
• Local electrical standards and design rules

A cable installed individually in open air may dissipate heat more effectively than the same cable installed in a crowded conduit on a hot roof. Temperature and grouping correction factors may therefore reduce the allowable current.

The PV circuit should be designed using the module short-circuit current, required safety factors, protective-device coordination, and the rules of the country where the system is installed.

Does System Voltage Determine Cable Size?

System voltage and cable voltage rating are important, but they do not directly determine the conductor cross-sectional area.

For example, both 4mm² and 6mm² solar cables may be manufactured for 1000V or 1500V DC photovoltaic systems. The voltage rating primarily depends on the insulation and cable construction. The conductor size is mainly selected according to current, voltage drop, temperature, and installation conditions.

A higher-voltage PV system can transfer the same power at a lower current. Lower current can reduce conductor losses, but the cable must still have the appropriate voltage rating and certification.

Temperature and Installation Environment

Solar cables are often exposed to demanding environments. Rooftop temperatures can be considerably higher than the surrounding air temperature, especially when cables are installed close to dark roofing materials or underneath solar modules with limited airflow.

High conductor temperature increases electrical resistance and voltage drop. It can also reduce the available current-carrying capacity.

A 6mm² cable may provide additional margin for:

• Hot climates
• Metal rooftops
• Bundled PV cables
• Long conduit installations
• Poorly ventilated cable routes
• High continuous operating current

Nevertheless, increasing conductor size does not replace proper cable routing, ventilation, protection, and installation practices.

Connector and Cable Compatibility

Before changing from 4mm² to 6mm² cable, confirm that every component is compatible with the selected conductor and cable outside diameter.

Check the specifications of:

• PV connectors
• Connector metal contacts
• Crimping tools and dies
• Combiner box terminals
• Inverter DC terminals
• Cable glands
• Junction boxes
• DC isolators

A connector may accept both 4mm² and 6mm² conductors, but the correct metal contact and sealing range must still be used. Poor crimping or an incorrect cable seal can create excessive contact resistance, overheating, moisture entry, and premature failure.

Cost Difference Between 4mm² and 6mm² Cable

6mm² cable contains more copper and normally has a larger overall diameter, so its purchase cost is higher. It is also heavier and may require larger cable glands, connectors, or installation accessories.

However, cable price should not be evaluated separately from lifetime energy loss. A lower-cost 4mm² cable can become less economical if a long cable route causes continuous resistive losses throughout the operating life of the PV system.

For short runs, the energy-saving benefit of 6mm² cable may be small. For long runs or high-current circuits, the reduction in voltage drop may justify the additional investment.

How to Choose Between 4mm² and 6mm² Solar Cable

Use the following process when selecting the cable size:

1. Determine the design current. Use module and string electrical data, including short-circuit current and the safety factors required by local regulations.
2. Measure the one-way cable distance. Include the actual routing distance, not only the straight-line distance.
3. Calculate voltage drop. Calculate the complete positive and negative circuit length.
4. Check installation conditions. Consider temperature, conduit, bundling, ventilation, and exposure.
5. Apply correction factors. Use the applicable local standard or engineering design method.
6. Check component compatibility. Verify connectors, terminals, glands, and crimping tools.
7. Compare lifetime cost. Consider both cable price and long-term power loss.

Frequently Asked Questions

Is 6mm² solar cable always better than 4mm²?

No. A 6mm² cable has lower resistance, but it is also more expensive, heavier, and thicker. For a short cable run with moderate current, 4mm² may provide acceptable performance at a lower cost.

Can I connect 4mm² cable to a 6mm² solar cable?

Different cable sizes can be used in the same system when the circuit is properly designed, but every section must be suitable for the current and protected correctly. Connections should be made using approved terminals or connectors that are compatible with both cable sizes.

Can 4mm² solar cable be used in a 1500V PV system?

Conductor size and voltage rating are separate characteristics. A 4mm² cable may be used in a 1500V system only when the cable construction, insulation, certification, current capacity, and voltage-drop calculation are suitable for that system.

Is 6mm² cable required for high-wattage solar panels?

Not automatically. Panel wattage alone does not determine cable size. Check the module operating current, short-circuit current, number of parallel strings, cable length, and installation conditions.

What cable size is normally used between solar panels and an inverter?

Both 4mm² and 6mm² solar cables are commonly used. The correct choice depends on current, distance, allowable voltage drop, temperature, installation method, and local electrical requirements.

Does a larger solar cable improve panel output?

A larger cable does not increase the power generated by the solar panels. However, it can reduce resistive losses, allowing more of the generated energy to reach the inverter.

Final Recommendation

Choose 4mm² solar cable when the circuit current is moderate, the cable route is relatively short, installation conditions are favorable, and the calculated voltage drop is acceptable.

Choose 6mm² solar cable when the cable route is longer, the current is higher, the environment is hot, several cables are grouped together, or the project requires lower voltage drop and reduced long-term energy loss.

The final decision should be based on an electrical calculation rather than cable size alone. Always verify the cable certification, DC voltage rating, conductor resistance, temperature rating, connector compatibility, and local installation requirements.