What is motor starting current?

Motor starting current (inrush current) is the initial surge of current when a motor is first energized. For DOL (direct-on-line) starting, it is typically 6–8 times the rated full-load current and lasts until the motor reaches operating speed.

Why is starting current so high?

At standstill, the rotor does not generate back-EMF, so the motor winding impedance is very low, resulting in high current. As the motor accelerates, back-EMF builds up and current drops to the normal running value.

What is the difference between DOL and star-delta starting?

DOL (direct-on-line) applies full voltage immediately, giving 6-8× rated current. Star-delta starts in star connection (1/3 voltage per winding), reducing starting current to about 1/3 of DOL values (2-3× rated), then switches to delta for normal running.

How does a VFD reduce starting current?

A Variable Frequency Drive (VFD) controls both voltage and frequency, ramping them up gradually. This allows the motor to start with only 1–1.5× rated current while still providing adequate starting torque.

What is the NEMA code letter for locked rotor current?

NEMA code letters (A through V) indicate the locked rotor kVA per HP. For example, code letter F means 5.0–5.6 kVA/HP. The starting current can be calculated as I_start = (kVA/HP × HP × 1000) / (√3 × V).

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Calculadora de corriente de arranque del motor

Calcule la corriente de arranque (pico) del motor para los métodos DOL, estrella-triángulo, arrancador suave y VFD. I_arranque = k_arranque × I_nominal.

DOL 6–8× Estrella-Triángulo 2–3× VFD 1–1.5×

Potencia nominal del motor (kW)

Voltaje de línea (V)

Factor de potencia cos φ (0–1)

Eficiencia η (0–1)

Método de Arranque

Multiplicador de arranque k (×I_rated)

Preajustes rápidos

Resultados

Corriente de arranque I_start

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Corriente nominal a plena carga I_rated

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Multiplicador de arranque k

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Potencia aparente de arranque

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Método de Arranque

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Corriente Nominal

Corriente de arranque

Comparación de métodos de arranque

Método	Multiplicador de corriente	Par de frenado	Uso Típico
DOL	6–8 × I_nominal	Completa	Motores pequeños < 7.5 kW
Estrella-Delta	2–3 × I_nominal	~33%	Bombas, ventiladores, 7.5–75 kW
Arrancador Suave	2–4 × I_nominal	Variable	Transportadores, compresores
VFD	1–1.5 × I_nominal	Completa	Cualquiera, mejor control

Ejemplo — Motor de 15 kW, Arranque DOL

Datos: P = 15 kW, V = 400 V, cos φ = 0.85, η = 0.91, DOL k = 7

I_nominal = 15000 / (√3 × 400 × 0.85 × 0.91) = 28.0 A

I_arranque = 7 × 28.0 = 196.0 A

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Resultados

Corriente Nominal

Corriente de arranque

Comparación de métodos de arranque

Tienda

Soporte

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