The question of whether stranded wire carries more current than solid wire has a straightforward answer for most everyday situations. A solid wire consists of a single conductor, while stranded wire is composed of multiple, thinner wires twisted together. For standard direct current (DC) or low-frequency alternating current (AC) uses, the current-carrying capacity (ampacity) is determined by the total amount of copper, not the construction. The American Wire Gauge (AWG) system ensures that a stranded wire and a solid wire of the same gauge designation have the same nominal cross-sectional area.
How Wire Gauge Determines Current Capacity
The current capacity of a conductor is governed by its electrical resistance and the heat it can safely dissipate. Resistance is defined by the material’s resistivity, its length, and its cross-sectional area. The relationship is expressed by the formula R = resistivity Length / Area.
The American Wire Gauge system ensures a wire’s gauge number corresponds directly to its total metallic cross-sectional area. This means a 12 AWG solid wire contains the same nominal volume of copper as a 12 AWG stranded wire, resulting in nearly identical resistance over the same length. When current flows through this resistance, power is lost as heat (Joule heating), quantified by the formula P = Current^2 Resistance.
Ampacity tables determine the maximum safe current by limiting the heat generated to prevent insulation damage. Since resistance and heat dissipation are essentially the same for equivalent-gauge solid and stranded conductors at standard AC frequencies (like 60 Hz) or DC, the current rating is also the same. Any minor difference in resistance between the two constructions is negligible for general power applications.
Mechanical Properties of Wire
While electrical capacity is the same for equivalent gauges, mechanical properties dictate different best-use scenarios. Solid wire is rigid and maintains its shape well, which is advantageous for permanent installations. Its stiffness makes it easier to push through conduits and secure under terminal screws without fraying.
Stranded wire is significantly more flexible because the total conductor area is distributed across many smaller, independently moving strands. This flexibility is useful in applications involving movement or vibration, such as robotic arms, automotive wiring, or extension cords. Stranded wire also resists metal fatigue, making it less likely to break when bent repeatedly. This durability makes it the preference for any temporary or moving electrical connection.
High-Frequency Current and the Skin Effect
An exception to the equal ampacity rule occurs when dealing with high-frequency alternating current, explained by the “skin effect.” This effect causes AC current to flow primarily along the outer surface of a conductor, rather than being uniformly distributed. Higher frequencies result in shallower penetration, effectively reducing the available cross-sectional area for current flow and increasing resistance.
For a thick solid wire carrying high-frequency current, the center of the conductor is barely used, leading to significant power loss and heating. Stranded wire counters this problem because its construction increases the total surface area available for current flow. The current flows over the surface of every individual, thin strand, rather than just the outer surface of a single large conductor.
Specialized constructions, such as Litz wire, take this principle further by individually insulating and carefully weaving the strands so that each wire spends time on the bundle’s exterior. This ensures the current is distributed more evenly across the entire bundle, significantly mitigating the skin effect and proximity effect. In these high-frequency applications, a stranded conductor carries the current with much lower resistance than a solid wire of the same overall gauge.
Selecting the Right Wire for the Job
Choosing between solid and stranded wire balances electrical performance, mechanical needs, and signal frequency. Solid wire is the most cost-effective choice for fixed, permanent wiring installations, such as wiring inside walls. It is also favored for grounding applications where stiffness and durability are beneficial.
Stranded wire is selected for applications requiring repeated flexing, such as appliance cords, patch cables, and internal wiring for machinery or vehicles. Its resistance to fatigue ensures a longer lifespan in dynamic environments. When a circuit involves high-frequency signals (e.g., RF equipment or high-end audio), stranded wire—especially Litz construction—is necessary to minimize power loss caused by the skin effect.