Motor Start Up Current Calculator Based On

Start I = Rated I × KVA Code Factor

\[ I_{start} = I_{rated} \times K_{code} \]

Rated Current (I):

KVA Code Factor:

Start Up Current (I_start):

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1. What Is Motor Start Up Current Calculation?

Motor start up current calculation determines the initial current drawn by an electric motor during startup, which is typically several times higher than the rated operating current. This calculation is essential for proper circuit protection and equipment sizing.

2. How Does The Calculator Work?

The calculator uses the formula:

\[ I_{start} = I_{rated} \times K_{code} \]

Where:

\( I_{start} \) — Start up current (A)
\( I_{rated} \) — Rated current (A)
\( K_{code} \) — KVA code factor based on motor design

Explanation: The KVA code factor represents the locked-rotor kVA per horsepower, which determines the starting current multiplier for the motor.

3. Importance Of Start Up Current Calculation

Details: Accurate start up current calculation is crucial for selecting appropriate circuit breakers, fuses, and overload protection devices to prevent nuisance tripping while ensuring motor protection.

4. Using The Calculator

Tips: Enter the motor's rated current in amperes and select the appropriate KVA code from the motor nameplate. All values must be valid (rated current > 0).

5. Frequently Asked Questions (FAQ)

Q1: What is KVA code on a motor?
A: KVA code is a letter code found on motor nameplates that indicates the locked-rotor kVA per horsepower, which determines the starting current characteristics.

Q2: Why is start up current higher than running current?
A: During startup, the motor rotor is stationary, creating maximum counter-EMF and drawing maximum current until the motor reaches operating speed.

Q3: How long does start up current last?
A: Start up current typically lasts from a fraction of a second to several seconds, depending on motor size, load, and design.

Q4: Can start up current damage the motor?
A: Properly designed motors can handle start up current, but repeated starts or extended starting periods can cause overheating and damage.

Q5: How does this affect electrical system design?
A: Start up current determines the sizing of conductors, circuit protection devices, and may require special starting methods for large motors.