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.
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
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
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