ANSI Code Impedances

Impedance Multipliers for ANSI Std. Short Circuit Calculations


Code


Motor

Momentary Duty
First Cycle

Interrupting Duty
1.5 - 4 Cycles

Synch

Synchronous

1.0 X"dv

1.5 X"dv

Ind>1000

Induction Motor > 1000 Hp

1.0 X"dv

1.5 X"dv

> 250 @ 3600

Induction Motor > 250 Hp at 3600 RPM

1.0 X"dv

1.5 X"dv

>50

Induction Motor or Motor Group > 50 Hp

1.2 X"dv

3.0 X"dv

<50

Induction Motor Group < 50 Hp

1.67 X"dv

Infinite X"dv

Lumped

Lumped Induction Motor Group

1.0 X"dv (X=25%)

3.0 X"dv

Note: X" for induction motor groups >50 HP and <50 HP are typically assumed equal to 16.7%. Using the impedance multipliers, this corresponds to an equivalent motor contribution of 3.6 to 4.8 times the full load current.

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