PEC Cable Sizing Commercial
Beyond a certain current, a single conductor becomes impractical — running conductors in parallel has its own rules.
At high enough current, a single conductor per phase becomes physically impractical — too large to bend, terminate, or even source. Running two or more conductors in parallel per phase is a standard solution, with its own specific requirements.
Parallel conductors must be electrically identical — same length, same material, same size, same insulation type, and generally the same physical routing — so current divides evenly between them. Mismatched parallel runs can result in one conductor carrying disproportionately more current than its share, effectively undermining the whole point of paralleling.
Even a modest length difference between parallel runs changes their relative resistance, which skews current division away from equal. A parallel set routed through different conduit paths of different lengths is a common way this requirement gets violated without anyone noticing until a thermal issue shows up.
Parallel conductors become worth considering once single-conductor sizes exceed what's practical to source, bend, and terminate reliably — a threshold that varies by project and supplier availability, not a single universal current figure.
Engr. Jason Morales — Founder, SolarEnergyPH & OhmWorks