Solar cable specifications use two different systems for indicating conductor size: AWG (American Wire Gauge) common in North America, and mm² (square millimeters) used internationally. Understanding both systems and their conversion is essential for proper cable selection in global solar projects.
AWG System Fundamentals
The American Wire Gauge system originated in the 19th century for standardizing wire manufacturing. AWG uses a counter-intuitive numbering system where smaller numbers indicate larger conductors.
Key AWG Characteristics:
Smaller AWG numbers = larger conductor cross-section
Each decrease of 3 AWG numbers approximately doubles the cross-sectional area
Each decrease of 6 AWG numbers approximately doubles the diameter
AWG scale is logarithmic, not linear
Common solar cable AWG sizes include 14 AWG, 12 AWG, 10 AWG, and 8 AWG for residential installations, with larger sizes like 6 AWG, 4 AWG, and 2 AWG for commercial projects. Utility-scale installations may use 1/0 AWG, 2/0 AWG, or larger.
The "0" designation indicates sizes larger than 1 AWG. These are sometimes written as 1/0 (pronounced "one-ought"), 2/0, 3/0, and 4/0, with larger numbers indicating bigger conductors—reversing the typical AWG pattern.
Metric System (mm²) Fundamentals
The metric system expresses conductor size as cross-sectional area in square millimeters. This measurement directly indicates the conductor's area, making comparisons straightforward.
Metric System Advantages:
Directly represents actual conductor area
Linear relationship between size number and cross-section
Intuitive comparison—larger number always means larger conductor
Simplifies resistance and current capacity calculations
Common PV cable metric sizes include 2.5mm², 4mm², 6mm², 10mm², 16mm², and 25mm² for typical installations, with larger sizes like 35mm², 50mm², 70mm², and 95mm² for utility-scale projects.
Conversion Between Systems
Converting between AWG and mm² requires reference tables as no simple formula provides exact conversion. The systems developed independently and don't align precisely.
Common Solar Cable Conversions:
14 AWG ≈ 2.5mm²
12 AWG ≈ 4mm²
10 AWG ≈ 6mm²
8 AWG ≈ 10mm²
6 AWG ≈ 16mm²
4 AWG ≈ 25mm²
2 AWG ≈ 35mm²
These are approximations. Exact cross-sectional areas don't match perfectly. For example, 12 AWG has an actual area of 3.31mm², while 4mm² nominal size typically has 4.0mm² actual area. For critical applications, verify actual conductor area rather than relying solely on size designation conversions.
Regional Specification Differences
North American Projects: Solar installations in the United States, Canada, and Mexico typically specify cable sizes in AWG. Project specifications, electrical codes (NEC), and equipment ratings use AWG sizing.
International Projects: Most other regions including Europe, Asia, Africa, and South America use metric sizing. IEC standards, which dominate global solar specifications, reference conductor sizes in mm².
Multinational Projects: Large solar developers working globally must navigate both systems. Equipment from US manufacturers may specify AWG, while European inverters reference mm² sizing. Proper conversion ensures compatible component selection.
Ampacity Differences
Current carrying capacity (ampacity) depends on several factors beyond conductor size, including insulation type, installation method, and ambient temperature. This creates additional complexity when comparing AWG and metric conductors.
A 10 AWG conductor and a 6mm² conductor have similar cross-sectional areas, but ampacity ratings may differ slightly based on:
Testing standard used (UL vs IEC)
Assumed installation conditions
Insulation material specifications
Temperature rating differences
Always verify ampacity from manufacturer specifications rather than assuming equivalent ratings between nominally similar AWG and mm² sizes.
Voltage Drop Calculations
Conductor resistance determines voltage drop, and this calculation requires actual conductor area. When working with AWG sizes, first convert to actual mm² area before calculating resistance and voltage drop.
Standard resistance tables provide values for both AWG and metric sizes at specified temperatures. Using the correct resistance value for your conductor size and temperature ensures accurate voltage drop calculations.
Specification Accuracy
When specifying solar cables for international projects, identify which sizing system the specification requires:
For AWG Specifications: Use exact AWG sizes. Don't specify "approximately 12 AWG" or "equivalent to 12 AWG"—specify 12 AWG explicitly if that's the requirement.
For Metric Specifications: Use standard metric sizes (2.5mm², 4mm², 6mm², etc.). Avoid non-standard sizes unless specifically required.
For International Procurement: Specify both AWG and mm² if cables might be sourced from multiple regions. For example: "12 AWG (4mm²)" provides clarity for suppliers using either sizing system.
Connector Compatibility
Solar connectors specify compatible conductor size ranges, typically in both AWG and mm². Verify that selected cable size falls within connector specifications.
Some connectors designed for AWG sizing may not perfectly accommodate metric equivalents due to slight size differences. This particularly affects crimp connectors where precise conductor fit is critical for proper connection.
Standards and Testing
UL Standards: US testing standards typically reference AWG sizing in requirements and test procedures.
IEC Standards: International standards use metric sizing throughout specifications.
When cables require certification to multiple standards, manufacturers must navigate both sizing systems and ensure compliance across different measurement frameworks.
Practical Procurement Guidance
When sourcing solar cables internationally:
Identify governing standard (NEC/UL or IEC) for your project
Use appropriate sizing system for that standard
Verify actual conductor area in manufacturer specifications
Confirm ampacity ratings rather than assuming equivalence
Check connector compatibility with actual conductor dimensions
Specify tolerance requirements if precise sizing is critical
Common Confusion Points
"Equivalent" Sizing: Suppliers sometimes offer "AWG equivalent" metric cables or vice versa. Verify actual specifications rather than relying on equivalence claims, as sizes may not match exactly.
Stranding Differences: AWG and metric conductors may use different stranding configurations (number and size of individual strands). This affects flexibility and installation handling even when cross-sectional areas are similar.
Insulation Differences: UL-listed cables and IEC-certified cables may use different insulation types and thicknesses, affecting overall cable diameter even with similar conductor sizes.
Conclusion
Understanding both AWG and mm² sizing systems enables proper solar cable selection for projects worldwide. While conversion tables provide approximate equivalents, always verify actual conductor specifications, ampacity ratings, and standards compliance when working across sizing systems.
For multinational projects, explicitly specify sizing requirements in the appropriate system for your region and standards, ensuring suppliers provide properly sized conductors that meet all project requirements.
