Motor Calculator
Single-motor branch-circuit sizing from NEC Tables 430.248 (1Ø) and 430.250 (3Ø) for full-load current, conductors at 125% (430.22), maximum branch-circuit short-circuit and ground-fault protection from Table 430.52, and overload sizing from 430.32. These table values are the same in the 2020 and 2023 editions (the 2023 edition renamed the 430.52 table and added Design B premium-efficiency wording). Use the nameplate only for overloads. This is not for HVAC equipment under Article 440 — use the nameplate MCA and MOCP there.
430.52 permits the next higher standard size if the percentage does not land on a standard rating (Exception 1). If that device will not let the motor start, Exception 2 allows a higher ceiling (commonly 400% for an inverse-time breaker) — this calculator reports the Exception 1 maximum only. Wound-rotor and DC motors use different 430.52 percentages; this tool uses the single-phase / AC polyphase squirrel-cage columns. Overloads are sized from nameplate FLA when you enter it (430.32); otherwise the table FLC is used as a stand-in — enter the nameplate.
Table 430.248 — single-phase FLC (A)
Table 430.250 — three-phase FLC (A)
Also available on the Breaker / OCPD page.
Reference only — not engineering, legal, or code-compliance advice. Results are estimates for qualified persons and must be verified against the NEC edition adopted where the work is done (your selected edition), manufacturer instructions, and the local AHJ. Use is subject to the Terms of Use & Disclaimer. — Morningstar Electric LLC