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NEC Art.430
Validated against the standard.
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How it works
Enter your values
Type in your inputs — the app fills code tables and constants for you, so there's nothing to look up.
Get a code-checked result
Instant answer with a clear PASS / FAIL and the exact NEC Art.430 reference behind every number.
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Keep a history of calculations and export a clean PDF report to share or attach to a permit (Pro).
What this calculator does
Motor circuits have their own rules in NEC Article 430. The key one trips up a lot of people: for sizing conductors and branch protection you use the table full-load current (FLC) from 430.248 (single-phase) or 430.250 (three-phase) — not the nameplate amps. This app looks up the FLC, then sizes the conductors, overload, and short-circuit protection around it.
The Article 430 sequence
- FLC — look up the motor in Table 430.248 or 430.250 by horsepower and voltage.
- Conductors (430.22) — at least 125% of the FLC for a single continuous-duty motor.
- Overload (430.32) — sized from the motor nameplate FLA, typically 115% or 125% depending on service factor and temperature rise.
- Branch protection (430.52) — short-circuit and ground-fault device sized as a percentage of FLC from Table 430.52, with a next-size-up allowance.
Worked example — 5 HP, 230 V, three-phase
Table 430.250 FLC for 5 HP at 230 V three-phase = 15.2 A.
Conductors: 125% x 15.2 = 19 A → #12 copper. Inverse-time breaker (430.52): 250% x 15.2 = 38 A → next standard size 40 A.
Overload from the nameplate FLA at 125% (typical) protects the motor itself. The app shows each step with its article.
Related calculators
Size the feeders with the wire size calculator and the protection with the breaker size calculator.
Motor FLA FAQ
Why use the table FLC instead of the nameplate?
NEC 430.6(A)(1) requires the full-load current values in Tables 430.248 and 430.250 — not the nameplate amps — for sizing conductors and branch-circuit protection. The nameplate FLA is used only for the overload device.
How are the conductors sized?
For a single continuous-duty motor, conductors must carry at least 125% of the table FLC, per 430.22. The app applies this and then picks the conductor from the ampacity tables.
What about the breaker or fuse?
Branch-circuit short-circuit and ground-fault protection is sized from Table 430.52 — for example 250% of FLC for an inverse-time breaker — with the next-standard-size-up allowance in 430.52(C).
Single-phase and three-phase?
Both. The app uses Table 430.248 for single-phase and Table 430.250 for three-phase motors across standard horsepower and voltage ratings.
Does it work offline?
Yes, it runs 100% offline with no account. Free with rewarded ads; a one-time $2.99 Pro unlock adds PDF export and saved history.
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