Parallel Conductors: When and How to Use Them
Learn when parallel conductors are the right solution for voltage drop and high-current circuits. Includes NEC requirements, sizing methods, and installation best practices.
Understanding Parallel Conductors
Parallel conductors provide an effective solution when a single conductor cannot meet current-carrying requirements or when voltage drop limits demand very large conductor sizes that would be impractical to install. By running multiple smaller conductors in parallel, electricians can achieve the equivalent of very large conductors while maintaining workable installation conditions. Understanding when and how to apply parallel conductors is essential for large commercial and industrial electrical installations.
The NEC permits parallel conductors under specific conditions outlined in Section 310.10(G). These requirements ensure that current divides equally among the parallel conductors and that the installation is safe and reliable. Failure to follow these requirements can result in unequal current sharing, overheating, and potential failures.
NEC Requirements for Parallel Conductors
NEC 310.10(G) Key Requirements
- Minimum Size: Parallel conductors must be 1/0 AWG or larger (for copper or aluminum)
- Same Length: All parallel conductors must have the same length
- Same Material: All must be copper or all aluminum (no mixing)
- Same Size: All conductors in each phase must be the same circular mil area
- Same Insulation: All must have identical insulation type and temperature rating
- Same Termination: All must terminate in the same manner
Voltage Drop Calculations for Parallel Conductors
When calculating voltage drop for parallel conductors, the effective resistance is divided by the number of conductors per phase. This is because the parallel paths share the current, effectively reducing the total resistance of the circuit.
Parallel Conductor Formula
Where R is the resistance of a single conductor and N is the number of parallel conductors per phase
Example: 800A Feeder
An 800A feeder at 480V three-phase, 300 feet long. Using 4 sets of 350 kcmil copper (R = 0.0382 Ω/kft)
Reff = 0.0382 / 4 = 0.00955 Ω/kft
Vd = (1.732 × 800 × 300 × 0.00955) / 1000
Vd = 3.97 volts (0.83%)
Installation Best Practices
- Phase Arrangement: Group one conductor from each phase together in each raceway to minimize inductive heating effects. This is especially important for steel conduit.
- Equal Length: Measure and cut all parallel conductors to exactly the same length. Even small differences can cause unequal current sharing.
- Termination: Ensure all parallel conductors terminate properly and torque all connections to manufacturer specifications.
Calculate Parallel Conductor Voltage Drop
Our calculator supports parallel conductor configurations. Enter your parameters and number of parallel sets to get accurate voltage drop results for high-current installations.
Parallel Conductor Calculator