Motor Running Overload Protection (NEC 430.32)
Running overload protection for a motor, sized on the nameplate FLA.
Example
You enter
- Nameplate full-load current FLA (A) 26
- Marked service factor (blank if unmarked) 1.15
- Marked temperature rise (°C, blank if unmarked) 40
You get
- Mult 1.25
- Overload setting 32.5
- 430.32(C) maximum (will not start) 36.4
Checked against published worked examples from: EC&M (Mike Holt).
Details, formula, and sources
ScopeThe running overload for a motor, sized on the NAMEPLATE FLA (not the table FLC the branch-circuit device uses) - the second of the two motor protection devices. NEC 430.32(A)(1) gives 125% of FLA for a continuous-duty motor over 1 hp with a marked service factor of 1.15+ or a marked rise of 40 C or less, 115% otherwise, and 430.32(C) permits raising to 140%/130% only if the motor will not start at the base setting. A 26 A SF-1.15 motor sets at 32.5 A with a 36.4 A ceiling - the number dialed into the overload relay or the heater table. A design aid; the AHJ governs.
Formula or tablehi_class = (sf >= 1.15) or (marked rise <= 40 degC); mult = hi_class ? 1.25 : 1.15; mult_max = hi_class ? 1.40 : 1.30; ol_A = fla_A x mult; ol_max_A = fla_A x mult_max.
Source and editionMotor running-overload sizing on the nameplate full-load current under NEC 2023 430.32(A)(1) (125% for a marked service factor of 1.15 or more or a marked temperature rise of 40 degC or less, 115% otherwise) with the 430.32(C) will-not-start ceiling (140%/130%), by name. A computational aid; the AHJ-adopted NEC edition governs.
Free accessNEC is free to read at nfpa.org/freeaccess. The 430.32(D) hand-started small motor and 430.36 fuse-as-overload are stated as out of scope, not modeled; a thermal protector integral with the motor is the 430.32(A)(2) option (added 2026-10-08), and a motor of 1 hp or less, automatically started, is the 430.32(B) option (added 2026-10-09).
What governsEstimate. AHJ and licensed electrician govern. Verify against the NEC edition adopted in your jurisdiction.
API field namesfla_A, sf, rise_C, mult, ol_A, ol_max_A
- Basis current the motor NAMEPLATE FLA, not the 430.6 table FLC the 430.52 branch device usesNEC 430.32 / 430.6(A)
- Class selection 125%/140% for marked SF >= 1.15 or marked rise <= 40 degC; 115%/130% otherwise; an unmarked (blank) value does not qualifyNEC 430.32(A)(1) and (C)
- Scope a continuous-duty motor over 1 hp, or 1 hp or less automatically started, with a separate overload device or an integral thermal protectorNEC 430.32(A) and (B)
- Thermal protector option ultimate trip no more than 170% (9 A or less), 156% (9.1-20 A), or 140% (over 20 A) of the TABLE full-load currentNEC 430.32(A)(2)
- 1 hp or less, automatically started a separate device takes the same 125%/115% rule and 430.32(C) ceiling; an integral thermal protector has no percentage ceiling, only approval for the motor it protectsNEC 430.32(B)(1) and (B)(2)