3 phase motor circuit breaker sizing calculator

A very specific and technical request!

Here's a simple 3-phase motor circuit breaker sizing calculator:

Inputs:

1. Motor Power (kW): Enter the power rating of the motor in kilowatts (kW).
2. Motor Voltage (V): Enter the voltage rating of the motor in volts (V).
3. Motor Current (A): Enter the current rating of the motor in amperes (A).
4. Fault Current (A): Enter the fault current rating of the motor in amperes (A).
5. Short-Circuit Current (A): Enter the short-circuit current rating of the motor in amperes (A).
6. Circuit Breaker Type: Select the type of circuit breaker (e.g., molded case, air-break, or vacuum).

Calculations:

1. Motor Full-Load Current (A): Calculate the motor full-load current using the formula: Motor Full-Load Current = Motor Power (kW) / Motor Voltage (V) / Power Factor (PF). Assume a power factor of 0.8 for this calculation.
2. Motor Locked-Rotor Current (A): Calculate the motor locked-rotor current using the formula: Motor Locked-Rotor Current = Motor Full-Load Current x 1.5 (a common factor for most motors).
3. Circuit Breaker Rating (A): Calculate the circuit breaker rating using the formula: Circuit Breaker Rating = Maximum of (Motor Full-Load Current, Motor Locked-Rotor Current, Fault Current, Short-Circuit Current).

Example:

Let's say we have a 3-phase motor with the following specifications:

• Motor Power: 15 kW
• Motor Voltage: 480 V
• Motor Current: 25 A (full-load current)
• Fault Current: 100 A
• Short-Circuit Current: 200 A
• Circuit Breaker Type: Molded case

Calculations:

1. Motor Full-Load Current: 25 A
2. Motor Locked-Rotor Current: 25 A x 1.5 = 37.5 A
3. Circuit Breaker Rating: Maximum of (25 A, 37.5 A, 100 A, 200 A) = 200 A

Result:

The recommended circuit breaker rating for this 3-phase motor circuit is 200 A.

Note:

• This calculator is a simplified example and may not account for all the complexities of a real-world circuit.
• It's essential to consult the motor manufacturer's specifications and follow relevant electrical codes and standards (e.g., NEC, IEC) for accurate circuit breaker sizing.
• This calculator is intended for general guidance only and should not be used as the sole basis for designing or sizing electrical circuits.