ANSI Fault Analysis

A_FAULT provides fault calculations in full compliance with the ANSI C37 standards.

It offers separate solutions for low, medium and high voltage systems and for symmetrical, momentary and interrupting calculations as defined in the standards.

For medium and high voltage systems, the momentary and interrupting values may be calculated using either the E/X or E/Z methods permitted by the standards. Both ac and dc decrement curves required by the total current rated standard (C37.5) and the symmetrical rated standard (C37.010) are used by the program.


  • Design safer power systems by calculating equipment ratings per ANSI standards.
  • Save time by automatically applying ANSI C37 and IEEE 141 multiplying factors to generators and motors.
  • Increase efficiency with custom data reporting featuring X/R, E/X or E/Z methods and values for the application of low, medium, and high voltage breakers.
  • Communicate effectively with quality reports.


  • Reports three-phase, single-line to ground, line to line, and double line to ground fault values.
  • Reports values for both total current and symmetrical rated breakers.
  • Models transformer primary and secondary taps and off nominal rated voltages.
  • Use either ac/dc, dc only, interpolated or no ac decay options.
  • Reports calculated remote/local status for each generator.
  • Interrupting study reports total and symmetrical 2, 3, 5, 8 and 30 cycle values.
  • Complies with ANSI standards and IEEE recommended procedures.
  • Provides separate network solutions for reporting X/R values.
  • Momentary and interrupting studies can report E/X or E/Z values.
  • Low voltage study complies with ANSI C37.13.
  • Momentary and interrupting studies comply with ANSI C37.010 and C37.5.
  • Custom reports using datablocks or crystal reports.
  • Display study results on the one-line.
  • User defined pre-fault voltage.


A_FAULT Versus DAPPER Traditional Fault Analysis

A_FAULT follows ANSI C37 standards for calculating equipment ratings.

DAPPER follows a traditional Ohm’s Law calculation for fault current.

For Low voltage systems (600V and below), the calculations are the same except for two items: 1) A_FAULT calculates the X/R ratios based on separate X and R networks whereas DAPPER uses a single complex network. 2) A_FAULT uses the X/R ratio to adjust the calculated short circuit value to compare directly with molded case and power circuit breaker ratings based on ANSI test power factor. In other words, the calculated short circuit value is increased if the X/R ratio is larger than the ANSI test power factor.

For Medium and High Voltage systems (above 600Volts): The momentary calculations are similar. The largest difference is in Interrupting Calculations: A_FAULT uses the ANSI C37 tables and curves to simulate AC and DC decay for interrupting calculations, whereas DAPPER accounts for the system DC decay but ignores the AC machine decay in all cases.