Motor Branch-Circuit from Nameplate
Compute full-load current from HP / V / eta / PF; flag the design value as the larger of computed vs nameplate.
Example
You enter
- HP 5
- Voltage (V) 230
- Phase 1
- Efficiency (eta, 0.5-1.0) 0.875
- Power factor (0.5-1.0) 0.78
- Nameplate FLA (A, optional) 28
- Service factor (1.0-1.4) 1.15
You get
- Computed FLA (A) 23.76
- Design FLA (A; larger of two) 28
- Branch conductor (125% rule, A) 35
- Overload max (A) 35
Details, formula, and sources
125% branch-conductor + overload sizing.
Single-phase: I = HP * 746 / (V * eta * PF). Three-phase: I = HP * 746 / (sqrt(3) * V * eta * PF). Branch-circuit conductor at 125% per NEC §430.22; overload max at 115% or 125% per NEC §430.32 (SF >= 1.15 -> 125%).
NEC 2023 (NFPA 70). §430.6(A)(1) (reference-FLA tables), §430.22 (branch conductor 125% rule), §430.32 (overload sizing).
Free read-only access at nfpa.org/freeaccess.
Estimate. AHJ and licensed electrician govern. Verify against the NEC edition adopted in your jurisdiction.
Field names used by the API: hp, voltage_V, phase, eta, power_factor, nameplate_fla_A, service_factor, computed_fla_A, design_fla_A, branch_conductor_125pct_A, overload_max_A
- Reference-FLA tables NEC 430.247 / 430.248 / 430.250 are NOT reproduced; the physics output is a companion to (not a substitute for) the table valueNEC 2023 §430.6(A)(1)
- Design FLA larger of computed vs nameplate when nameplate is providedengineering practice
- Overload multiplier 125% for SF >= 1.15; 115% otherwiseNEC 2023 §430.32