Solar Cable Size Guide: 4mm², 6mm², 10mm² and Current Capacity

Solar cable size must satisfy the circuit’s required current after derating, the project’s voltage-drop limit and the equipment’s connection requirements. A 4mm² conductor may meet a short string circuit’s requirements, while a longer route or combined output may require 6mm², 10mm² or more. Panel wattage alone cannot determine the answer.

We recommend recording the calculation assumptions beside each selected cross-section. This makes a solar cable size decision reviewable when the installer changes the route, adds circuits to a tray or substitutes a connector.

Select the smallest permitted solar cable size that passes every electrical, installation and termination check. Passing an ampacity calculation does not establish acceptable voltage drop, fault protection or connector compatibility.

Start with the actual circuit: a module string, combined DC output, battery connection and inverter AC output require different sizing inputs. Our guide to what a solar cable is explains these application boundaries.

For solar cable size calculations, collect the following information before comparing cross-sections:

Series-connected modules increase string voltage; parallel strings increase combined current. For example, three equal strings carrying 13 A each contribute approximately 39 A to a shared output conductor at that operating point. That arithmetic is an illustration, not the completed code-based design current.

Do not substitute maximum-power current for the required PV sizing current without checking the design rules. Apply the relevant irradiance, continuous-current and other factors through the adopted calculation method; a single multiplier should not be presented as universal.

The temperature along the cable route and the number of loaded circuits can reduce the usable current capacity. A rooftop cable beneath closely spaced modules may experience different cooling conditions from the same cable suspended in open air.

Use the installation temperature at the cable, rather than a weather forecast measured elsewhere. Where the route changes from open supports to crowded conduit, assess each section. The most restrictive section can determine the solar cable size for the run. [Source: LAPP, current-rating and cable-dimensioning guidance.]

Check connection limits separately:

• Conductor range: the terminal or contact must accept the specified cross-section and conductor construction.
• Cable diameter: the insulation or sheath must fit the connector’s stated sealing range.
• Temperature and current: equipment limits can constrain an otherwise acceptable cable.
• Assembly: use the specified contact, preparation dimensions and tooling.

For example, Stäubli lists 4mm² and 6mm² conductors with a 5.4–7.6 mm outer cable diameter for its MC4-Evo ready connector. A 10mm² conductor is outside that stated range. Increasing solar cable size can therefore require a different approved connection arrangement. [Source: Stäubli, MC4-Evo ready.]

Use 4mm² when it passes the complete design; consider 6mm² when the smaller conductor fails the current or voltage-drop requirement. A larger conductor reduces resistance, but the benefit must be assessed against cable cost and connection compatibility.

Compare 4mm² and 6mm² using the same conductor material, circuit current, route length and conductor temperature. Otherwise, the comparison mixes size effects with differences in installation or construction.

The resistance comparison follows R = ρL/A; actual cable resistance should come from the supplier’s datasheet. Strand construction and manufacturing tolerances mean a nominal-area ratio is only an initial comparison.

For a two-conductor DC circuit, calculate ΔV = I × (Rpositive + Rnegative) using resistance at the expected conductor temperature. If the module-to-inverter distance is 40 m and both conductors follow that route, the current path contains approximately 80 m of conductor.

Suppose a 4mm² circuit has a calculated drop of 6 V. Under the idealized area comparison, 6mm² would reduce that to about 4 V. At a 400 V operating point, the drops are 1.5% and 1.0% respectively. These are calculated illustrations, not product test results or universal acceptance limits.

This is why solar cable size can increase even when the operating current remains unchanged.

Consider 10mm² or larger when 6mm² cannot meet the corrected ampacity or voltage-drop requirement. Combined outputs and long runs deserve a separate calculation rather than an automatic extension of the string-cable specification.

A larger cable cannot correct an underrated connector or unsuitable wiring method. If the required solar cable size exceeds the equipment’s connection range, the designer must specify an approved termination or transition arrangement.

There is no universal amp rating for 4mm², 6mm² or 10mm² solar cable. Published values depend on the cable construction, temperature assumptions and physical arrangement.

Read the rating together with its reference conditions. The following example comes from LAPP’s ÖLFLEX SOLAR H1 BUR datasheet, using its IEC 62930 table at 30°C ambient.

The datasheet separately states 90°C for normal continuous conductor operation and limits operation at 120°C to 20,000 hours. These published examples are not HUALUO product ratings or installation approvals. [Source: LAPP, DB38115805EN, version 04, pages 2–3.]

When reviewing a quotation, request the table’s ambient and conductor temperatures, installation arrangement, grouping assumptions and applicable standard. A current figure without this basis is insufficient to approve a solar cable size.

Apply correction factors that belong to the selected rating method and actual installation. A general expression is:

Corrected ampacity = reference ampacity × temperature factor × applicable grouping factor × other required factors.

Do not apply a factor twice for a condition already included in the selected table. Likewise, a factor taken from a different temperature basis may produce an incorrect result. [Source: LAPP, current-rating and cable-dimensioning guidance.]

For a temperature-only illustration, take the touching-cable column above. The same datasheet gives a 0.82 factor at 50°C ambient:

• 4mm²: 45 × 0.82 = 36.9 A.
• 6mm²: 58 × 0.82 = 47.6 A.
• 10mm²: 80 × 0.82 = 65.6 A.

If the already-established design requirement is 40 A, 4mm² fails this thermal comparison; 6mm² passes before further installation, protection and terminal checks. Additional grouped circuits may require another reduction. [Source: LAPP, DB38115805EN; calculations shown.]

We recommend keeping the selected solar cable size, table reference and correction factors on the same calculation sheet. That record prevents a later purchaser from replacing the cable using only an unqualified “maximum amps” claim.

Metric cross-sections and AWG designations are different sizing systems, so their common comparisons are approximate. A conversion chart helps interpret a specification; it does not approve a replacement.

4mm², 6mm² and 10mm² are larger than the commonly paired 12 AWG, 10 AWG and 8 AWG conductors. The table shows the area difference explicitly.

Percentages are calculated from the nominal areas. The AWG references are common commercial comparisons, not exact equivalents or a complete list of intermediate gauges.

A purchase specification requiring at least 6mm² nominal conductor area is not satisfied by 10 AWG on area alone. Any alternative needs a documented design review rather than a relabeled size.

A substitution must meet electrical requirements, product approvals and termination instructions together. Comparable conductor area does not establish the same insulation rating or permitted use.

Before accepting an alternative solar cable size, verify:

• Ampacity: recalculate using the proposed cable and installation basis.
• Voltage drop: use the replacement conductor’s resistance.
• Product identity: verify the required voltage rating, environmental suitability and certification scope.
• Termination: check conductor construction, contact size and sealing diameter.
• Project approval: record the accepted deviation from the original specification.

Our solar cable standards guide explains the distinction between product conformity and installation acceptance. Keep those checks alongside the size calculation when comparing metric and AWG offers.

For a project enquiry, review our solar cable range and send us the circuit specification, including design current, voltage, route length, installation method and required quantity. Include the selected solar cable size and calculation basis when the project designer has already approved them.