PEC Motors
Motor starting current is dramatically higher than running current — motor circuit sizing accounts for both.
A motor's inrush (starting) current can run several times higher than its steady running current — briefly, but with real thermal and voltage-drop consequences if the circuit isn't sized with that surge in mind, not just the nameplate running amperage.
| Value | What it drives |
|---|---|
| Full-load running current | Base conductor ampacity sizing, similar logic to any other continuous load |
| Locked-rotor / starting current | Overcurrent protective device sizing and starting-voltage-drop considerations, since breakers/fuses need to tolerate the brief surge without nuisance tripping |
A protective device sized purely to the running current would nuisance-trip every time the motor starts. Motor circuit design typically uses a higher-rated (but still coordinated) overcurrent device specifically tolerant of the brief starting surge, while the conductor itself is still sized to handle the continuous running current safely.
A motor that experiences excessive voltage drop during starting may fail to reach full torque, stall, or trip its own internal thermal protection — a separate, tighter voltage drop consideration from the general branch circuit limit, particularly relevant for larger motors on long feeder runs.
Engr. Jason Morales — Founder, SolarEnergyPH & OhmWorks