Parallel Conductor Ampacity
Total ampacity of paralleled conductor sets after the NEC fill and ambient adjustments.
Example
You enter
- Single-conductor ampacity (A) 200
- Number of parallel sets 3
- Ambient-correction factor (0-1) 1
- Conductor size (AWG / kcmil, 1/0+) 3/0
You get
- Total parallel ampacity 600
- Per set ampacity (A) 200
- Adjustment factor applied 1
Checked against published worked examples from: NEC (NFPA 70) Article 310 parallel-conductor provisions + 310.15(C)(1) adjustment.
Details, formula, and sources
ScopeTotal ampacity of N paralleled conductor sets with the NEC more-than-three current-carrying-conductor and ambient adjustments, plus per-set load adequacy (1/0 AWG and larger only).
Formula or tableI_total = I_single x N x F_ccc x F_ambient, where N is the number of identical parallel sets, F_ccc is the more-than-three current-carrying-conductor adjustment (1.0 for <=3, 0.8 for 4-6, 0.7 for 7-9, 0.5 for 10-20, ...), and F_ambient the temperature correction. Per-set current I_set = I_load / N. Paralleling is permitted only at 1/0 AWG and larger.
Source and editionNEC (NFPA 70) Article 310 paralleled-conductor provisions and the 310.15(C)(1) adjustment factors, by name.
Free accessNFPA 70 free read-only at nfpa.org/freeaccess; conductor ampacities user-supplied from the adopted edition's ampacity table.
What governsEstimate. AHJ and licensed electrician govern. Verify against the NEC edition adopted in your jurisdiction.
API field namesi_single_A, n_sets, ambient_factor, conductor_size, i_total_A, per_set_ampacity_A, adjustment_factor
- Conductor ampacity single-conductor ampacity user-supplied from the NEC ampacity table for the conductor / insulation / terminationNEC ampacity tables
- Parallel sets identical all parallel sets share length, material, size, insulation, and terminationNEC Article 310 parallel-conductor rule