When most electrician hear the words “industrial control panel” the first thing that comes to mind is a large control panel that comes as part of a listed piece of electrical equipment such as an industrial chiller or air conditioner or machinery.

An industrial control panel can be something large and elaborate created by a known manufacturer or, according to the Article 100 definition, an industrial control panel can be as simple as installing two lighting contactors in an enclosure to control parking lot lighting.

Article 100 Definitions.

Industrial Control Panel. 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.

The industrial control panel does not include the controlled equipment.

Once an industrial control panel has been constructed, NEC^® Article 409 now applies. NEC^® Section 409.22 requires that an industrial control panel cannot be installed at a location in the circuit where the Available Fault Current (AFC) is higher than the short-circuit current rating (SCCR) of the control panel.

In any circuit, the maximum AFC will be different at the beginning of the circuit than at the end due to impedance in the circuit. The longer the run of circuit conductor, the less AFC at the end of the circuit. Ensuring that an industrial control panel is never installed where the AFC is greater than the control panels SCCR can be accomplished in several ways:

• Install a control panel with a SCCR equal to or greater than the AFC.
• Use the proper fuse ahead of the passive control panel and refer to the fuse chart to ensure that it will never let through more current during a fault than the SCCR of the control panel.
• Determine the required size of the feeder or branch circuit conductors needed to supply the industrial control panel. Next, through calculations, determine the minimum length of feeder or branch circuit conductor needed to ensure that the AFC at the control panel is equal to or less than the SCCR of the control panel.

See the actual NEC^® text at NFPA.ORG for the complete code section. Once there, click on the “free access” tab and select the applicable year of NFPA 70 (National Electrical code).