Multiple Motor Feeder & Service Calculator
Add multiple motors and optional non-motor loads to size a feeder conductor and feeder OCPD under NEC Article 430 — two distinct calculations (430.24 and 430.62) with FLC table lookups, a step-by-step trace, and six common-mistake guards built in.
Overview
Sizing a feeder that serves more than one motor is one of the most-missed calculations in Article 430 because two different rules apply to the same feeder: 430.24 sizes the feeder conductor (125% of the largest motor FLC plus 100% of every other motor FLC plus any non-motor load), while 430.62 sizes the feeder OCPD (the largest branch-circuit OCPD plus the FLC of every other motor plus the non-motor load) — and the 'largest motor' can be a different motor in the two rules. This calculator handles both. Add any number of motors (HP, phase, voltage, code letter, service factor, design B/E/etc.) and optional non-motor loads (continuous or non-continuous). The tool pulls each motor's Full Load Current from NEC Tables 430.247–430.250 automatically, picks the largest FLC and the largest branch-circuit OCPD, and produces the minimum feeder conductor ampacity (430.24) and the maximum feeder OCPD (430.62) side by side. The Dashboard tab returns the sized feeder conductor and OCPD with pass/fail on every mandatory 430 check. The Calc Trace tab prints the derivation with citations to 430.6, 430.24, 430.52, 430.62, 430.247–.250, and 240.6. The Design Challenge tab generates randomized multi-motor scenarios. The Results tab is a printable calc sheet. The Code Refs tab summarizes each section used, and the Scope & Limits tab is explicit about what the tool does not cover (feeder demand under 430.26, tap conductors under 430.28). The Learn tab covers the six most common mistakes — using nameplate FLA instead of Table FLC, applying 125% to every motor, using the same 'largest' motor for both rules, forgetting non-motor continuous 125%, rounding OCPD the wrong direction, and confusing branch vs. feeder OCPD. A Self-Test tab runs the calculation logic against deterministic test cases. Supports NEC 2017, 2020, and 2026.
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 NEC 430.24 to size a feeder conductor for multiple motors — 125% of the largest motor FLC plus 100% of every other motor FLC plus any non-motor load
- 02Apply NEC 430.62 to size a feeder OCPD for multiple motors — largest branch-circuit OCPD plus the FLC of every other motor plus any non-motor load, rounded down to the next standard 240.6 size
- 03Look up motor Full Load Current from NEC Tables 430.247, 430.248, 430.249, and 430.250 and explain why nameplate FLA is not used for these sizing rules
- 04Recognize that the 'largest motor' in 430.24 (largest FLC) and the 'largest motor' in 430.62 (largest branch-circuit OCPD) can be different motors on the same feeder
- 05Add continuous and non-continuous non-motor loads to a motor feeder and apply the 125% continuous multiplier correctly
- 06Diagnose the six most common multi-motor feeder mistakes and explain why each produces an incorrect or non-compliant result
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