Solar cable sizing requires two separate electrical checks: corrected current-carrying capacity and voltage drop over the actual cable route. The selected cable must also meet the project’s voltage rating, installation rules and connector requirements. A 6mm² cable has lower resistance than 4mm², but neither size is a universal choice for solar panels.
If you are comparing 4mm or 6mm solar cable, start with operating current, string operating voltage, one-way route length and installation conditions. Consider 10mm² when the calculation justifies a larger conductor and the equipment accepts it.
Need a quotation for a PV project? Send your destination country, required cable standard, size options and quantity. Include current, voltage and route length if the size still needs review.
Request a solar cable quotation
Solar cable size chart: mm² and AWG
Cable size describes nominal conductor cross-sectional area. It does not describe the cable’s outside diameter. In buying enquiries, “4mm solar cable” usually means 4mm² conductor area; write the squared unit on the purchase specification.
| Metric conductor size | Nearby common AWG size | Nominal area of that AWG size | Procurement interpretation |
|---|---|---|---|
| 2.5mm² | 14 AWG | 2.08mm² | Different sizes; confirm the specified system |
| 4mm² | 12 AWG | 3.31mm² | 12 AWG has less nominal area |
| 6mm² | 10 AWG | 5.26mm² | 10 AWG has less nominal area |
| 10mm² | 8 AWG | 8.37mm² | 8 AWG has less nominal area |
| 16mm² | 6 AWG | 13.3mm² | 6 AWG has less nominal area |
| 25mm² | 4 AWG | 21.2mm² | 4 AWG has less nominal area |
AWG areas are rounded reference values; see Victron Energy’s AWG conversion chart. The nearby sizes are comparisons, not approved substitutions. Do not label 6mm² cable as 10 AWG unless the actual product and its approval support that marking.
For cable construction, insulation, sheath and product standards, read our solar cable specification guide.
4mm², 6mm² or 10mm²: what changes?
| Selection point | 4mm² solar cable | 6mm² solar cable | 10mm² solar cable |
|---|---|---|---|
| Resistance at the same material and temperature | Highest of these sizes | Lower than 4mm² | Lowest of these sizes |
| Reason to evaluate it | A route where corrected ampacity and voltage drop both meet requirements | More voltage-drop margin than 4mm² | Longer routes or higher current where calculation supports it |
| Handling | Usually lighter and easier to route within the same cable family | Check bend radius and cable diameter | More termination space may be needed |
| Connector check | Confirm the approved contact and seal | Confirm both conductor size and cable diameter | Confirm the exact connector variant accepts 10mm² |
| Selection limit | No universal current or length limit | No automatic safety approval from size alone | Larger size does not solve an incompatible connector |
In the simplified resistance model, moving from 4mm² to 6mm² reduces conductor voltage drop by one-third. Moving from 6mm² to 10mm² reduces it by 40%. These comparisons assume identical length, current, copper resistivity and conductor temperature; actual cable datasheet resistance should govern procurement calculations.
Solar cable voltage drop formula
For a two-conductor DC circuit with equal positive and negative conductor lengths and sizes:
ΔV = 2 × L × I × ρθ / A
Voltage drop (%) = 100 × ΔV / Vop
Conductor power loss (W) = I × ΔV
| Symbol | Input or output | Unit |
|---|---|---|
| ΔV | Voltage lost across both conductors | V |
| L | One-way conductor route length | m |
| I | Operating current in the circuit section being calculated | A |
| ρθ | Copper resistivity at the assumed conductor temperature | Ω·mm²/m |
| A | Conductor cross-sectional area | mm² |
| Vop | Operating voltage at the sending end of that section | V DC |
The factor of 2 includes the return conductor. A 50m one-way route means 100m of conductor in this model. If you enter the total positive-plus-negative length, omit the factor of 2. For unequal lengths or sizes, calculate each conductor’s resistance separately and add them.
Use operating current, typically Impp for a string, for the stated operating-point loss calculation. Use the applicable code design current for ampacity and protection. These can be different values.
Likewise, operating voltage belongs in the voltage-drop percentage calculation. Maximum system voltage requires a separate check using temperature-corrected open-circuit voltage and equipment limits.
Adjusting resistance for conductor temperature
For the worked examples, use this approximate copper model:
ρθ = ρ20 × [1 + α × (θ − 20)]
The example assumptions are ρ20 = 0.0175 Ω·mm²/m and α = 0.00393/°C, with θ in °C. The coefficient is documented in the NIST Copper Wire Tables; 0.0175 is the rounded resistivity assumed for these illustrations, not a certified resistance for any offered cable.
At a 60°C conductor temperature:
ρ60 = 0.0175 × [1 + 0.00393 × (60 − 20)] = 0.020251 Ω·mm²/m
For a product-specific check, use its maximum DC conductor resistance at 20°C, r20, in Ω/km:
ΔV = I × (2 × L / 1000) × r20 × [1 + α × (θ − 20)]
The division by 1000 converts meters to kilometers. This approach accounts for the resistance specified for the actual stranded conductor. Add connection losses separately where the design requires them.
Three worked PV cable sizing examples
All three examples use copper, equal positive and negative conductors, the approximate resistivity model above and an assumed 60°C conductor temperature. They exclude connector and terminal resistance.
The 2% target is an illustrative project criterion, not a universal IEC or NEC limit. The results assess conductor voltage drop only. They do not establish corrected ampacity, protective-device suitability or permission to install a particular size.
Example 1: 50m route, 13A operating current
Inputs: 50m one way, 13A, 415V DC operating voltage and 60°C conductor temperature.
For 4mm²:
ΔV = 2 × 50 × 13 × 0.020251 / 4 = 6.582V
Voltage drop = 100 × 6.582 / 415 = 1.586%
| Size | Voltage drop | Voltage drop percentage | Conductor loss at this operating point |
|---|---|---|---|
| 4mm² | 6.58V | 1.59% | 85.56W |
| 6mm² | 4.39V | 1.06% | 57.04W |
| 10mm² | 2.63V | 0.63% | 34.22W |
All three fall below the example’s 2% target. That leaves ampacity, installation, protection and termination checks to determine which options remain suitable.
Example 2: the same string with a 100m route
Inputs: 100m one way, 13A, 415V DC and 60°C conductor temperature.
For 6mm²:
ΔV = 2 × 100 × 13 × 0.020251 / 6 = 8.775V
Voltage drop = 100 × 8.775 / 415 = 2.115%
| Size | Voltage drop | Voltage drop percentage | Comparison with the example’s 2% target |
|---|---|---|---|
| 4mm² | 13.16V | 3.17% | Above target |
| 6mm² | 8.78V | 2.11% | Above target |
| 10mm² | 5.27V | 1.27% | Below target |
Doubling the route doubles conductor voltage drop at the same current. Of these three sizes, only 10mm² meets this example’s voltage-drop target; it still requires all other design checks.
Example 3: a combined section carrying 26A
Inputs: 50m one way, 26A, 415V DC and 60°C conductor temperature. The 26A represents an illustrative combined operating current, not a code-derived ampacity requirement.
For 10mm²:
ΔV = 2 × 50 × 26 × 0.020251 / 10 = 5.265V
Voltage drop = 100 × 5.265 / 415 = 1.269%
| Size | Voltage drop | Voltage drop percentage | Conductor loss at this operating point |
|---|---|---|---|
| 4mm² | 13.16V | 3.17% | 342.24W |
| 6mm² | 8.78V | 2.11% | 228.16W |
| 10mm² | 5.27V | 1.27% | 136.90W |
Examples 2 and 3 produce the same voltage drop because length multiplied by current is equal. Example 3 has twice the conductor power loss of Example 2 at each size because its current is twice as high. Instantaneous loss in watts is not an annual energy-loss estimate.
Calculate each string-to-combiner section separately from the combined section. Adding strings in parallel increases current only in the conductors that carry the combined output.
Solar cable sizing calculator: compact calculation block
This manual calculation block lets you reproduce the examples with a calculator or spreadsheet. It estimates voltage drop and a conductor area based on voltage drop only.
Inputs
| Input | Example value | What to enter |
|---|---|---|
| One-way length, L | 50m | Actual routed conductor length |
| Operating current, I | 13A | Current in this circuit section |
| Operating voltage, Vop | 415V DC | String or section operating voltage |
| Conductor temperature, θ | 60°C | Assumed operating conductor temperature |
| Candidate area, A | 6mm² | Size being evaluated |
| Voltage-drop target, d | 2% | Enter 2 in the formulas below, not 0.02 |
| Copper resistivity at 20°C | 0.0175 Ω·mm²/m | Approximate model assumption |
Calculations and outputs
ρθ = 0.0175 × [1 + 0.00393 × (θ − 20)]
ΔV = 2 × L × I × ρθ / A
Drop (%) = 100 × ΔV / Vop
Loss (W) = I × ΔV
Minimum area for voltage drop only (mm²) = 200 × L × I × ρθ / (Vop × d)
Maximum one-way length for voltage drop only (m) = d × A × Vop / (200 × I × ρθ)
| Output using the example inputs | Result |
|---|---|
| Voltage drop across both conductors | 4.39V |
| Voltage drop percentage | 1.06% |
| Conductor power loss | 57.04W |
| Calculated minimum area for the 2% target | 3.17mm² |
| Calculated maximum one-way length with 6mm² | 94.58m |
| Comparison with the entered target | Below 2% for voltage drop only |
The calculated 3.17mm² is a mathematical threshold, not an available cable specification or a recommendation to order 4mm². Select an approved standard size and repeat the checks using actual cable resistance and corrected ampacity. A value close to the target needs particular care because this simplified model excludes connection losses.
For this block, use positive length, current, voltage and area; d must be a positive percentage. Keep the copper temperature approximation within 20°C to 90°C. The block does not calculate conductor temperature from load, ambient temperature or installation conditions.
Need the product data to complete the comparison? Request 4mm², 6mm² and 10mm² cable datasheets and pricing. Include your calculation inputs, required standard and quantity per size.
Temperature, grouping and installation corrections
Voltage drop and ampacity use different temperature inputs. Resistance calculations use conductor temperature. Ampacity correction tables usually start with ambient air or ground temperature and a stated conductor temperature limit.
Select a reference ampacity for the actual installation method, then apply the compatible factors:
Corrected ampacity = Reference ampacity × k_temperature × k_grouping × other applicable factors
Do not apply a factor twice if its effect is already included in the reference rating.
For example, Schneider Electric’s IEC-based guide gives 0.82 at 50°C ambient for the applicable XLPE/EPR in-air method referenced to 30°C ambient. Its table also gives 0.80 for two circuits bunched together under the stated arrangement. If a compatible reference rating were an assumed 50A:
50 × 0.82 × 0.80 = 32.8A
The 50A is an arithmetic assumption, not a rating assigned here to 4mm², 6mm² or 10mm². Verify circuit counting, insulation category and table conditions before using these factors. Source: Schneider Electric’s general method for cable sizing.
| Site condition | Information needed before selecting a size |
|---|---|
| Hot rooftop route | Local cable ambient conditions, solar exposure and equipment temperature limits |
| Multiple circuits together | Circuit count, spacing, arrangement and applicable grouping method |
| Conduit or enclosed section | Installation method, occupancy and heat dissipation |
| Underground section | Permitted cable type, burial method, soil conditions and mechanical protection |
| Several conditions on one route | Check each section; the limiting section can determine the size |
An ampacity table based on a 120°C conductor cannot automatically justify continuous operation at that temperature. Confirm the cable’s permitted temperature duration and the lower limits of connectors and equipment. Request the rating conditions with every supplier ampacity figure.
IEC and NEC solar cable sizing: keep the methods separate
Projects using IEC-based installation rules
Establish the applicable national adoption and editions first. IEC 60364-7-712 addresses PV installations; IEC 60364-5-52 addresses wiring-system selection and erection. IEC 62548-1 covers PV array design, including DC wiring and protection. The IEC catalogue lists IEC 62548-1:2023 with Amendment 1:2025.
Determine design current using the applicable PV rules, including relevant module and array conditions. Then check corrected current-carrying capacity, protection and voltage drop. A simple Impp entry in the calculation block does not complete that process.
Cable product standards and installation calculations have different roles. EN 50618 or IEC 62930 documentation does not establish the correct size for a particular route. Our PV1-F vs H1Z2Z2-K guide explains the product-designation differences.
Projects governed by the NEC
Use the NEC edition adopted by the local jurisdiction and confirm requirements with the authority having jurisdiction. Review Article 690 for PV circuits, the applicable Article 310 ampacity provisions and equipment termination limits under 110.14(C).
In the NEC 2023 framework, 690.8(B) requires comparison of the conductor requirement without adjustment/correction factors and the requirement with those factors. A familiar 1.56 × Isc shortcut does not, by itself, establish the final conductor size or cover every circuit configuration. Maximum circuit current, applicable exceptions, terminations and protection still need review.
NFPA’s public code-development record documents this distinction; use the adopted code itself for design, available through the official NFPA 70 page.
Do not transfer an IEC metric ampacity table into an NEC calculation or assume that an IEC cable certificate establishes US listing acceptance. Specify the required cable listing, conductor designation and wiring method separately.
Connector compatibility can limit the cable choice
A cable can meet the voltage-drop target and still be unsuitable for the selected connector. Before changing size, confirm:
- Connector manufacturer, series and exact part numbers.
- Approved conductor size, class and strand construction.
- Cable outside diameter and approved sealing range.
- Current and temperature ratings for the assembled connection.
- Required contacts, stripping dimensions and assembly tools.
- Inverter, combiner-box and terminal acceptance.
“MC4 compatible” is insufficient purchasing information. Use the approved mating combination and assembly instructions for the exact products. A visually similar connector is not proof of compatibility.
For an H1Z2Z2-K specification, review our H1Z2Z2K solar cable product page and request the offered cable’s diameter and resistance data. If the contract specifies PV1-F, use the PV1-F product enquiry and confirm the required approval before accepting an alternative.
What to send for a solar cable quotation
A useful enquiry separates the engineering inputs from the purchasing requirements. If the engineer has already approved the size, attach the cable schedule and specify that size directly.
| RFQ field | Information to provide |
|---|---|
| Destination and rules | Project country, applicable code edition and required approvals |
| Cable specification | Type, standard, conductor material and size in mm² or AWG |
| Electrical inputs | Impp, Isc, operating voltage, maximum design voltage and parallel-string arrangement |
| Route | One-way length and the circuit section it describes |
| Site conditions | Ambient temperature, exposure, grouping, conduit, tray or burial details |
| Voltage-drop criterion | Target percentage and the route sections included |
| Connections | Connector model, accepted conductor size, diameter range and terminal limits |
| Quantity and packing | Meters per size and color, reel length, labels and destination |
| Documents | Datasheet, relevant certificate, test report and batch traceability requirements |
Ask the supplier to state maximum conductor resistance at 20°C, cable diameter, construction tolerances and the assumptions behind any ampacity figures. Match certificate scope to the offered product and size range.
For inverter AC output and other distribution circuits, use a separate design calculation. Our low voltage power cable guide covers the wider product category.
Frequently asked questions
Should I choose 4mm or 6mm solar cable?
Compare both at your actual length and current. In Example 1, their calculated conductor drops are 1.59% and 1.06%. Both are below the assumed 2% target, but corrected ampacity and connector checks still determine whether either is suitable.
How far can I run 6mm² solar cable?
There is no fixed distance. Under the calculation block’s assumptions of 13A, 415V, 60°C conductor temperature and a 2% target, the estimated one-way limit is 94.58m. Actual conductor resistance and connection allowances change that result.
Is 6mm² the same as 10 AWG?
No. The nominal area of 10 AWG is approximately 5.26mm². Confirm the required conductor designation, product approval and termination range before proposing a substitution.
Is a solar cable sizing calculator enough for installation?
A voltage-drop calculator can compare candidates. Final selection also requires code design current, corrected ampacity, protection, maximum voltage, installation suitability and connector checks. This page’s manual calculation block does not issue an installation approval.
Can ordinary building wire replace solar cable?
Only where the applicable rules, wiring method and product ratings permit it. Exposed PV routes require the relevant environmental and electrical suitability. A matching conductor size alone does not establish that suitability.
Request pricing for your approved cable size
Send your cable schedule, required standard and quantity to KingForYou Cable for a quotation. If you are comparing sizes, include the route inputs and ask for matching datasheets so your project engineer can complete the selection.
Safety and design scope: This guide provides educational calculations and procurement guidance. Its examples and calculation block are not project designs, installation instructions or compliance certification. A qualified electrical designer must verify the adopted rules, equipment instructions, circuit protection and site conditions before installation. PV circuits can remain energized in daylight; inspection and electrical work require appropriate isolation and qualified personnel.
