Motor Locked-Rotor Ampere Sizing

This tool calculates the maximum motor locked-rotor current, which is also known as LRA, in amperes for single and poly-phase Design B, C and D motors as per Table 430.251(A) and 430.251(B) of NEC (2011).

The LRA is the amount of current drawn by motor loads when the motors start (during startup motor is not turning).

The LRA is much larger than the full load ampere or FLA (the current drawn when motor is turning).

The rating calculated with this tool can be used in selection of disconnecting means and controllers for motors as determined from HP and voltage rating and design letter.

This app is tested with all iOS platforms including iPhone and iPad.