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.

AVAILABLEAUTOMATED CHECKS ONLYSTANDARDS-AWAREADVANCEDNECWHAT DO THESE STATUSES MEAN?

NEC • 430.24NEC • 430.62FLC TABLES 430.247–.250FEEDER + OCPD

Launch lab Sign in to bookmark Report an issue with this lab

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

Example data — not a real field report

Dashboard with motor list and sized feeder — Dashboard — add each motor (HP, phase, voltage, design letter) and any non-motor loads on the left, and the right pane returns the sized feeder conductor (430.24) and feeder OCPD (430.62) side by side with a pass/fail on every mandatory NEC check.

Printable engineering results — Results — full calc sheet: each motor's Table FLC, the largest FLC (for 430.24), the largest branch-circuit OCPD (for 430.62), the feeder conductor ampacity requirement, and the maximum feeder OCPD rounded to a standard 240.6 size.

Step-by-step calculation trace — Calc Trace — the full 430.24 and 430.62 derivations printed line by line with citations to 430.6, 430.24, 430.52, 430.62, 430.247–.250, and 240.6, so the sizing decision is defensible in a design review.

Design challenge mode — Design Challenge — randomized multi-motor scenarios (mixed HPs, phases, non-motor loads) with your submitted feeder conductor and OCPD graded against the correct answer, plus a diff of which rule tripped up the response.

NEC references summary — Code Refs — every applicable NEC 2017/2020/2026 section summarized with the exact FLC and OCPD values pulled from Tables 430.247–.250 and 240.6 for your inputs, so the lookup is verifiable by hand.

Explicit scope and limits — Scope & Limits — an explicit list of what the calculator covers (430.24 / 430.62 feeder sizing) and what it deliberately does not (feeder demand under 430.26, tap conductors under 430.28, service calculations) so the tool is not misapplied.

Learn tab with common mistakes — Learn — the six most common multi-motor mistakes explained: nameplate FLA vs. Table FLC, applying 125% to every motor, using the same 'largest' motor in both rules, missing continuous 125% on non-motor load, wrong OCPD rounding, and confusing branch vs. feeder OCPD.

Deterministic self-test harness — Self-Test — a deterministic test harness runs the calculation logic against known-answer multi-motor problems so you can verify the tool matches worked examples in the NEC Handbook and coursework.

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

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).