Feeder Conductor Size Calculator

Inputs

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Load expected to run 3 hours or more (NEC definition). Weighted at 125% for the termination path.
A
Remaining demand-factored load, weighted at 100%.
A
From the adopted ambient-temperature correction table for the conductor insulation rating (1.00 at the table reference ambient).
From the more-than-three current-carrying-conductors adjustment table (e.g. 0.8 for 4-6 CCC; 1.0 for up to 3).
Candidate conductor's ampacity from the adopted table at its insulation rating (often the 90°C column for THHN/XHHW-2 as the correction basis).
A
The SAME conductor's ampacity at the termination temperature column (75°C for most equipment; 60°C for some small/older gear).
A

Results

Default result
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Required at terminations(1.25·I_cont + I_non)
110A
Caution

Termination path passes with under 5% headroom; tolerance on load estimates can erase it.

The conductor termination-column ampacity must meet this, with no correction/adjustment applied.

Also computed

Corrected ampacity(I_table·k)Caution104A

Corrected path passes with under 5% headroom.

Candidate table ampacity after ambient correction and bundling adjustment.

Termination-path margin(ΔI_term)Caution5A

Corrected-path margin(ΔI_corr)Caution4A

The corrected-ampacity path (derating) is the binding constraint for this case.

Total load (100%)(I_cont + I_non)100A

Effective derating(k_amb·k_adj)0.8

Termination utilization(u_term)0.957

Method notes 4 notes
  • Structure follows NEC 215.2(A)(1)/210.19(A): conductors sized for 125% of continuous plus 100% of noncontinuous load at the terminations, AND corrected/adjusted ampacity not less than the load. Enter table values from the adopted code edition — this page embeds no code tables.
  • Exception path: with listed 100%-rated assemblies, the 125% continuous factor on that path does not apply — verify the equipment listing.
  • Motor, motor-compressor and welder loads have their own article-specific sizing rules layered on top.
  • Overcurrent protection, small-conductor caps (e.g. the 15/20/30 A rules), voltage drop on long runs and equipment terminations are separate checks.

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