About

Industrial environments typically operate on 3-phase power systems (380V, 400V, or 415V). Unlike single-phase systems where I = P/V, 3-phase calculations involve the square root of 3 (1.732) and the Power Factor (PF). Failing to account for a low Power Factor in induction motors can lead to significant underestimation of the current drawn, resulting in tripped breakers or melted cables. This tool provides the precise Line Current (Amps) required for proper cable sizing and circuit protection.

Formulas

The formula calculates Line Current for a balanced 3-phase load.

IAmps = PkW × 1000√3 × VLL × PF × η

Where VLL is Line-to-Line Voltage (typically 400V) and η is Efficiency (decimal, e.g., 0.9).

Reference Data

Motor Rating (kW)	Approx Current @ 400V (A)	Suggested Breaker
1.0 kW	~2.2 A	6A / 10A
5.5 kW	~10.8 A	16A
7.5 kW	~14.5 A	20A
11.0 kW	~21.0 A	25A
15.0 kW	~28.5 A	32A
22.0 kW	~41.0 A	50A
37.0 kW	~68.0 A	80A

Frequently Asked Questions

In a three-phase system, the power is delivered by three distinct waves offset by 120 degrees. The factor of square root of 3 relates the Line-to-Line voltage to the Line-to-Neutral voltage and accounts for the phase geometry.

If you calculate assuming PF=1.0 (Unity), your result will be lower than reality. Most motors have a PF between 0.8 and 0.9. This means the motor actually draws MORE current than the "perfect" calculation suggests, which is dangerous for wiring.

This calculator determines the Line Current drawn from the supply, which is the value needed for sizing supply cables and breakers, regardless of whether the internal motor winding is Star or Delta.