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Version 6.10
General Information
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All Volts Features
Branch Circuit Load Calcs
Circuit Layout
Cable Tray Fill
Circuit Load Analysis
Conduit Fill
Device and Metal Box Fill
Efficiency Factor
Motor Ampacity and Characteristics
Motor Startup Ampacity
Ohm’s Law
Power Factor
Power Factor Correction
Resistor Color Codes
Series Location Voltage Drop
Transformer Sizing
Unit Conversions
Utility Transformer Values
Wireway Fill
Circuit Breakers
Device and Metal Boxes
Arc Blast Pressure
Arc Flash Labels
Custom Reports
One Line Diagrams
Panel Schedules
Report PDF Samples
Short Circuit Analysis
Surge Protection Analysis
Formulae & Methods
Voltage Drop Formulae
Conductor Sizes
Ohm's Law Formulae
SI Units
Motor Startup Amperes (LRA)
  The Motor Startup Amperes module computes the approximate locked-rotor amperes (LRA) of an electric motor during its startup (motor start windings predominate) with the motor's nameplate letter code per NEC® Table 430.7(B). It also computes the running kilowatt and kilovolt amperes (apparent power) required to for the LRA demand based on the motor's nameplate values.


This module is necessary for sizing a generator that is used in conjunction with electric motors. The generator must be sized to supply the motor's startup amperage to prevent damage to the motor and protection devices from disengaging. Also as necessary, this module is used for Short Circuit and Arc Flash Analysis for the motor contribution values to a circuit when a fault is initiated.

After first selecting the letter code corresponding the the motor's nameplate, select the motor's power unit of measurement, enter values for power, volts and power factor and select the power phase. Its that easy to calculate the motor's locked-rotor amperage and the kilowatts and kilovolt amperes required for safe motor startup. The calculated results can be posted to the main Circuit Load Analysis module for further analysis.

The module's simple interface comprises a list box of the motor nameplate letter codes in the same format as NEC® Table 430.7(B), a list box of several motor nameplate real power units ,1, 2 or 3 Phase power, Power Factor, Volts, and Power Value. From there Volts does all the work.


It simply cannot be any easier or more accurate to obtain the correct information the first time.


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Reprinted with permission from NFPA 70 2008, NEC® copyright© 2008, National Fire Protection Association. This is not the complete and official position of the NFPA on the referenced subject which is represented only by the standard in its entirety. The title National Electric Code® and the acronym NEC® are registered trademarks of the National Fire Protection Association (NFPA).

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