Solar cable conductors come in two primary configurations: stranded and solid. Each design offers distinct characteristics affecting installation ease, mechanical durability, and long-term performance in photovoltaic systems.
Conductor Construction Fundamentals
Solid Conductors: A solid conductor consists of a single copper wire of specified diameter. This simple construction provides maximum conductivity per cross-sectional area with minimal manufacturing complexity.
Stranded Conductors: Stranded conductors comprise multiple smaller wires twisted together to achieve the desired cross-sectional area. Common configurations include 7-strand, 19-strand, 37-strand, and higher strand counts for larger conductors.
Flexibility and Installation Handling
Stranded Conductor Advantages: The primary benefit of stranded construction is superior flexibility. Multiple thin wires bend more easily than a single thick wire of equivalent area. This flexibility proves critical for solar installations requiring:
Routing cables through conduit with multiple bends
Installing cables in tight spaces or complex rooftop configurations
Making connections in junction boxes with limited working room
Accommodating thermal expansion and contraction movements
Installation crews generally prefer stranded conductors for field work, particularly in retrofit applications where cable routing presents challenges.
Solid Conductor Limitations: Solid conductors exhibit stiffness that complicates installation in confined spaces. Larger gauge solid conductors become progressively more difficult to bend and route. However, this rigidity provides advantages in straight-run applications where cables need to maintain specific routing paths.
Mechanical Durability Considerations
Vibration and Movement: Solar installations experience vibration from wind, thermal cycling, and structural movement. Stranded conductors handle these stresses better than solid conductors because individual strands can flex independently, distributing mechanical stress across multiple wires.
Solid conductors concentrate stress at bending points, creating potential failure locations with repeated flexing. This makes solid construction less suitable for applications with significant movement or vibration.
Fatigue Resistance: Laboratory testing demonstrates that stranded conductors withstand substantially more flex cycles before failure compared to solid conductors of equivalent cross-section. For PV cables subject to thermal expansion cycling over 25+ year lifetimes, this fatigue resistance provides important reliability benefits.
Electrical Performance Comparison
DC Resistance: Solid conductors offer slightly lower DC resistance than stranded equivalents because the entire cross-sectional area consists of continuous copper. Stranded conductors have small air gaps between individual strands, marginally reducing effective conductive area.
This difference typically remains under 2% for equivalent nominal sizes—negligible for most solar applications. The resistance advantage of solid conductors rarely justifies their installation difficulties.
Current Carrying Capacity: At equivalent cross-sectional areas, solid and stranded conductors have similar ampacity ratings. Installation conditions (temperature, bundling, exposure) affect ampacity more significantly than conductor construction type.
Skin Effect: For DC solar applications, skin effect (current concentration at conductor surface) does not occur. This AC phenomenon only affects performance in AC portions of solar systems, where it slightly favors stranded construction due to increased surface area from multiple strands.
Connection Reliability
Termination Methods: Stranded conductors require specific termination techniques. Compression lugs or crimped ferrules ensure all strands make solid electrical contact. Improper termination of stranded conductors—allowing loose strands—creates high-resistance connections and potential failure points.
Solid conductors terminate more simply since the single wire provides consistent contact surface. However, this advantage diminishes with proper installation practices and appropriate crimp tooling for stranded conductors.
Connector Compatibility: Most solar connectors accommodate both solid and stranded conductors within specified size ranges. However, connector manufacturers often optimize designs for stranded conductors given their prevalence in solar applications.
Standards and Code Requirements
Neither NEC (National Electrical Code) nor IEC standards mandate specific conductor construction for solar applications. Project specifications determine whether solid or stranded conductors are acceptable.
However, most solar cable standards reference stranded construction. IEC 62930 and EN 50618 specifications typically describe stranded conductors in their test requirements, reflecting industry preference for this construction type.
Cost Considerations
Manufacturing Costs: Solid conductors cost slightly less to manufacture due to simpler production processes. Stranded conductor production requires additional equipment for strand twisting and more complex quality control.
For solar cables, this cost difference typically represents 5-10% of conductor cost—a small fraction of total cable price when insulation and jacketing are included.
Installation Labor Costs: Installation efficiency differences often exceed material cost variations. Stranded conductors' easier handling reduces installation time, particularly in complex routing situations. This labor savings typically outweighs any material cost premium.
Application-Specific Recommendations
Choose Stranded Conductors For:
Standard solar installations with typical routing requirements
Rooftop systems with multiple direction changes
Applications requiring vibration resistance
Installations where future maintenance may require cable movement
Most commercial and utility-scale solar projects
Solid Conductors May Suffice For:
Simple straight-run applications with no routing complexity
Very short cable runs where flexibility isn't critical
Specific applications where code or specifications permit solid construction
Budget-constrained projects with simple installation conditions
Manufacturing Quality Factors
Stranding Quality: High-quality stranded conductors maintain uniform strand tension and consistent lay (twist pitch). Poor stranding allows individual strands to separate or creates uneven current distribution. Reputable manufacturers specify strand count, lay direction, and dimensional tolerances.
Material Consistency: Both solid and stranded conductors require consistent copper purity and proper annealing. Manufacturing quality affects both construction types equally, making supplier selection important regardless of conductor configuration.
Conclusion
Stranded conductors dominate solar cable applications due to superior flexibility, fatigue resistance, and installation ease. While solid conductors offer marginal electrical performance advantages, these benefits rarely outweigh the practical disadvantages for field installation.
For most solar cable applications, stranded construction represents the optimal balance of electrical performance, mechanical durability, and installation practicality. The industry-wide preference for stranded conductors reflects decades of field experience demonstrating reliable long-term performance.
