NEC Section 409.110 provides marking requirements for industrial control panels. Buying a listed industrial control panel ensures that the control panel will have the appropriate markings. In the event that an industrial control panel is field constructed, such as a 12 X 12 box with an overload relay and a push button, NEC^® 409.110 requires seven different items to be marked on the control panel. Item 4 can be easy or may require a bit of homework in order to pass inspection.

Section 409.110 item (4) requires the industrial control panel to be marked with the short-circuit current rating (SCCR) of the control panel unless the control panel contains only control circuit components. There are two methods permitted in 409.110(4) to determine the SCCR:

1. Use a listed and labeled control panel that will already be marked with the SCCR as part of the product listing requirement.
2. Determine the SCCR of the control panel using an approved method and mark it on the control panel. NEC^® Article 100 defines the term “Approved” as “Acceptable to the authority having jurisdiction” (the inspector).

The inspector may or may not want to be responsible for allowing item 2 above since it leaves liability in the hands of the inspection agency. The informational note mentions Supplement SB in UL 508A as an example of an “approved” method. The city inspector will generally not have a copy of the standard in order to know what Supplement SB actually says.

The method mentioned in UL 508A Supplement SB can be quickly summarized as follows:

• Determine the lowest SCCR of any individual component in the control panel.
• Determine if any current limiting devices are protecting the control panel.
• Mark the control panel with the SCCR based on the two items above.

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).

2014-2017 Code Language:

409.110 Marking. An industrial control panel shall be marked with the following information that is plainly visible after installation:

(4) Short-circuit current rating of the industrial control panel based on one of the following:

1. Short-circuit current rating of a listed and labeled assembly
2. Short-circuit current rating established utilizing an approved method

Informational Note: ANSI/UL 508A, Standard for Industrial Control Panels, Supplement SB, is an example of an approved method.

Exception to (4): Short-circuit current rating markings are not required for industrial control panels containing only control circuit components.