Available Fault Current on the Plans. Exercise 4.

Refer to the image to answer the question.
Click to Enlarge
Refer to the image to answer the question.

The image shows a short-circuit calculation chart also known as a fault current chart for a new construction project where a 150kVA (150,000-volt) dry-type transformer is installed. The transformer (TX) impedance is represented by TX %Z. The chart shows an Available Fault Current (AFC), also known as available short circuit current (ISC) at the secondary spades of the transformer of 16,654 amps.

After leaving the transformer with a single (not parallel) 25-foot run of 500 kCMIL copper conductor in a plastic raceway, the AFC at the end of the run of wire will be 14,741 amps at the electric panel that the transformer supplies.

Notice the comments provided by the electrical engineer at the top of the chart.

Did You Like This? Let Us Know With A Like! Thanks!

Available Fault Current on the Plans. Exercise 4.

Below is a Real Question from our Electrical Continuing Education Courses for Electrical License Renewal:

Refer to the image:

Which of the following is true?

A: The AFC at the secondary spades of the transformer is 14,741.
B: The AFC at the panelboard supplied by the transformer is 16,654.
C: The “C” value used is 22,815.
D: If a different transformer with an impedance of 2% is used, the engineer needs to be consulted to rework the short-circuit calculation.
Please register or sign in for electrical continuing education courses.

If you were already signed in, your session probably expired, please sign back in.