Motor Running Overload Protection (NEC 430.32)
The second of the two motor protection devices - the one motor-branch-protection defers: the running overload, sized on the NAMEPLATE FLA (not the table FLC the branch device uses). 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 and source
hi_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.
Motor 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.
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