Service & Feeder Conductor Sizing Calculator

Size service entrance and feeder conductors under NEC Articles 215 and 230 — with continuous-load factor, ambient and bundling correction, material and terminal temperature cap, voltage drop, and a design challenge mode.

AVAILABLEAUTOMATED CHECKS ONLYSTANDARDS-AWAREINTERMEDIATENECWHAT DO THESE STATUSES MEAN?

NEC • ART. 215 / 23090°C LOOKUP → TERMINAL CAP6 PRESET SCENARIOSDESIGN CHALLENGE MODE

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Overview

Service entrance and feeder conductors are among the most consequential sizing decisions in a project — undersized conductors create fire and voltage-regulation hazards, while oversized conductors waste material and create termination problems. This calculator works through the complete NEC sizing sequence under Articles 215 and 230: enter load in amps or kVA, select feeder or service, phase, and voltage, then configure continuous-load percentage, conductor material (copper or aluminum/CCA), 90°C insulation column lookup, terminal temperature rating cap (60°C or 75°C), ambient temperature, and bundling count. The tool applies all correction and adjustment factors in the correct NEC order and outputs the minimum compliant conductor size. The Results tab shows the final size with utilization gauge. The Trace tab provides a step-by-step NEC calculation walkthrough citing every section. The Charts tab plots ampacity-vs-size curves with operating point marked. Six presets cover Small Feeder (50 A), 3-Phase Service (200 A), Commercial Continuous Load, Hot Ambient Feeder, Aluminum Service, and Heavy Bundling. A Design Challenge mode generates randomized sizing problems with evaluated results. The Learn tab covers scope boundaries, common mistakes, the Pro Tip on correcting on the 90°C column then capping at the terminal rating, and the copper-vs-aluminum trade-off. Supports NEC 2017, 2020, and 2026 editions.

App preview

A live look at the app you'll launch — every control on the left drives the visualizations on the right in real time.

Inside the lab

Example data — not a real field report

Dashboard with rule-by-rule NEC code checks — Dashboard — every mandatory NEC check (ampacity, 110.14(C) terminal limit, 240.4 protection, continuous load) returns pass / warn / fail with the section cited, and the overall CODE PASS badge only lights when all mandatory checks pass.

Detailed results with conductor and OCPD selection — Detailed Results — selected conductor, terminal-limited ampacity, applied correction and adjustment factors, chosen OCPD, and voltage-drop advisory laid out for the design file.

Calculation trace with NEC citations — Calculation Trace — the entire sizing chain from load to conductor to OCPD is written out step by step with 310.16, 310.15(B), 110.14(C), 215.2, 230.42, and 240.4 citations.

Charts and graphs for ampacity and correction factors — Charts & Graphs — ampacity vs. size, ambient and bundling correction curves, and the effect of the 125% continuous multiplier visualized against your inputs.

Design Challenge with graded conductor selection — Design Challenge — randomized service or feeder scenarios ask you to size the conductor and OCPD; the tool grades your choice against the NEC.

Code references for Articles 215, 230, 240, and 310 — Code References — the Article 215 / 230 / 240 / 310 sections active for the current calculation, edition-aware across 2017 / 2020 / 2023.

Learn and quiz on service and feeder sizing — Learn & Quiz — terminal temperature limits, ampacity vs. required load, the 83% dwelling rule, continuous-load treatment, and a short quiz.

What you'll do

01Apply the NEC continuous-load multiplier (125%) to calculate minimum conductor ampacity for feeders and services under Articles 215 and 230
02Look up conductor ampacity from NEC Table 310.16 using the 90°C column, then cap the result at the terminal temperature rating (60°C or 75°C) per 110.14(C)
03Calculate the ambient temperature correction factor for conductors installed above 30°C and explain how it reduces allowable ampacity
04Determine the bundling adjustment factor for groups of 4 or more current-carrying conductors and apply it in the correct order with the temperature correction factor
05Select conductor material (copper vs. aluminum/CCA) given a known load and explain the trade-off in size, weight, and cost
06Trace every conductor sizing decision to the applicable NEC section and code table using the Calculation Trace tab

Try a guided scenario

Take a calculated load through to conductor and overcurrent device selection.

Service and feeder sizing · NEC Calculation Practice

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What this lab is not

Not a design document, stamped calculation, or approval record.
Not a substitute for engineering analysis by a licensed professional.
Not a reproduction of NEC tables — values are computed and cited, and you must verify against the code edition enforced in your jurisdiction.
Not connected to live equipment and not a safety device.

Calculation basis

References NEC. Results are computed from the entered inputs and cited back to the referencing clause or table number — no code text or table is reproduced verbatim.

Simplifying assumptions are stated in the lab itself; where a model is intentionally conceptual, the lab says so rather than implying study-grade accuracy.

Standards basis: Standards-aware. Validation state: Automated checks only (last checked 2026-08-15).