409.22 Short-Circuit Current Rating.

Try the FC2 calculator and compare your math to the old school calculation in the image. Change the length of wire to see how it impacts the available fault current.
Click to Enlarge
Try the FC2 calculator and compare your math to the old school calculation in the image. Change the length of wire to see how it impacts the available fault current.

An “industrial control panel” can be factory made and very elaborate or something as simple as two lighting contactors, field installed in a large junction box. Article 100 defines an Industrial Control Panel as an assembly of two or more components consisting of one of the following:

(1) power circuit components only, such as motor controllers, overload relays, fused disconnect switches, and circuit breakers;

(2) control circuit components only, such as push buttons, pilot lights, selector switches, timers, switches, and control relays;

(3) a combination of power and control circuit components. These components, with associated wiring and terminals, are mounted on, or contained within, an enclosure or mounted on a subpanel.

Section 409.22 requires industrial control panels to be installed at a point in the circuit where the available “short-circuit current” or available fault current (AFC) is equal to or less than the short-circuit current rating of the industrial control panel. As well, the industrial control panel must be marked to indicate how much short-circuit current is available at the control panel. The amount of short-circuit current refers to the amount of current that could be delivered to the industrial control panel under a short-circuit condition that may occur in the control panel.

These rules help to bring everything in compliance with NEC® 110.10. Knowing the amount of short-circuit current available at the industrial control panel is the first step in selecting the right control panel. For example, if a calculation is performed and it is found that the amount of short-circuit current available at a control panel is 4,999 amps, then installing an industrial control panel with a short-circuit current rating of 5,000 amps is code compliant.

Cooper Bussmann has a great fault current calculator called FC2 that can be downloaded to a smartphone or used online from any computer. This tool provides the amount of AFC at any given point in single and three-phase systems.

For complete code sections, refer to the actual NEC® text at NFPA.ORG. Once there, click on their link to free access to the 2017 NEC® edition of NFPA 70.

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

409.22 Short-Circuit Current Rating.

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

Which of the following is true of an industrial control panel with a short circuit current rating of 2,000 amps?

A: It must be installed at a location on the supply circuit where there is no more than 2,000 amps of available short circuit current.
B: It must be installed at a location on the supply circuit where there is no more than 4,000 amps of available short circuit current.
C: It must be installed at a location on the supply circuit where there is no more than 5,000 amps of available short circuit current.
D: It must be installed at a location on the supply circuit where there is no more than 6,000 amps of available short circuit current.
Please register or sign in for electrical continuing education courses.

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