NEC Article 430 — Motor Circuit Sizing

v1.1 · Engineering Reference Tool

Size branch-circuit conductors, OCPD, and overload protection for single or grouped motors per NEC 430.
Supports 1Ø and 3Ø motors across standard voltages — 115V through 575V — using NEC Table 430.248 / 430.250 FLC values.
Choose your OCPD type (TDF, NTDF, ITB, or Inverse-Time Breaker) — the tool auto-flags nuisance tripping risk and shows the Ex. 2 maximum when applicable.
Generates a printable schedule showing conductor ampacity, OCPD rating, conduit size, and voltage drop for every circuit.

⚠️ Engineering reference only. Always verify results against the applicable NEC edition, local amendments, and the Authority Having Jurisdiction (AHJ). Not a substitute for a licensed engineer's review.

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What's New

v1.1 — October 2026

Interactive tutorial — step through all major features from the splash screen or the header
Nuisance tripping auto-detection — tool now automatically flags NTDF or Design C/D motors and shows the Ex. 2 maximum; manual checkbox removed
Shareable URL — encode full job state into a link anyone can open
PDF export — download a formatted calc sheet with NEC reference notes
Responsive tablet layout
Feeder sizing per NEC 430.24 / 430.62

v1.0 — October 2026

Motor card redesigned — primary fields front and center, Advanced section for rarely-changed options
FLA (nameplate) field promoted to main motor inputs
Version badge and changelog added

Prior builds

NEC 430 branch circuit and feeder sizing engine
Circuit-based input form with unlimited motors per circuit
Save / load job as JSON
Conduit fill, voltage drop, OCPD, disconnect sizing
Non-motor loads (430.24)

Quick Tour — NEC 430 Motor Circuit Sizer

NEC 430

Motor Circuit Sizer · v1.0

Conductors OCPD Sizing OL Protection Disconnects

Welcome to NEC 430 Motor Circuit Sizer

A free engineering reference for sizing branch-circuit conductors, overcurrent protection, overload devices, and disconnecting means for AC motors — per NEC Article 430. This tour walks through the key features in about 2 minutes. Use ← → arrow keys to navigate.

+ Add Circuit

Circuit 1 — e.g. MCC-A Panel

HP ——

Voltage ——

Phase ——

Add Motor Circuits

Each circuit is one branch — a motor starter, MCC bucket, or panel circuit. Click + Add Circuit to add as many as the job needs. Give each one a name (e.g. "MCC-A Feeder") for easy reference in the results and PDF.

— Select HP —

Voltage

460V

Phase

3-Phase

FLA — Nameplate Amps (optional)

NEC FLC: 14.0 A → conductor min: 17.5 A (125% × FLC per 430.22)

Enter Motor Specifications

Select HP, system voltage, and phase. NEC Table 430.248/250 FLC is looked up automatically. Entering the nameplate FLA gives you more accurate 430.32 overload sizing — leave it blank to size from the NEC table value instead.

OCPD Type

Time-Delay Fuse (TDF)

Max multiplier per NEC 430.52 Table

10 HP / 460V: 14.0 A × 175% = 24.5 A → 25A TDF

175%

Choose Your OCPD Type

Select Time-Delay Fuse, Non-Time-Delay Fuse, Inverse-Time Breaker, or Instantaneous Trip CB. NEC Table 430.52 sets a different maximum multiplier for each type — the tool automatically rounds up to the nearest standard OCPD size.

Circuit 1 — Pump Room

10 HP · 460V 3Ø

5 HP · 460V 3Ø

3 HP · 460V 3Ø

+ Add Motor

Feeder sized per NEC 430.24:
125% × largest + 100% × others

Multiple Motors Per Circuit

Each circuit can hold multiple motors on a shared feeder. Click + Add Motor inside a circuit card to add tap motors. The tool applies NEC 430.24 feeder sizing automatically — 125% of the largest motor FLC plus 100% of all others.

▶ Calculate

✓ Circuit 1 — 10 HP / 460V 3Ø #12 AWG THHN

✓ OCPD: 25A TDF · OL: 17.5A ½" EMT

✓ Disconnect ≥ 16.1A (115% × FLC) 30A disc.

Run Your Calculation

Hit ▶ Calculate to generate the full NEC sizing schedule — conductor AWG & ampacity, conduit size and fill, OCPD rating, overload device, and disconnect for every circuit and motor. Every value is derived from the NEC code sections.

Save

Load

Share Link

Download PDF

✓ Link copied to clipboard!

Save, Share & Export

Save stores your job as a JSON file to resume later. Share Link copies a URL that restores every input — send it to a colleague or bookmark it. Download PDF generates a stamped calculation sheet ready for the job file or permit submittal.