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Short Circuit Current Ratings (SCCR) and Control Circuits

Question: Do the components in a control circuit have a short circuit current rating?

Answer: UL and NEC rules define which components in a control panel require a short circuit current rating.

Control circuit devices, such as pilot lights, push buttons, etc,do not have an SCCR, nor are they required per the NEC or UL 508A.

UL 508A September 2009 and NEC 2008 both talk about what is required to have an SCCR rating, and what is not.

The NEC 2008 (NFPA 70), 409.110 states: "Exception to (3)Short-circuit current rating markings are not required for industrial control panels containing only control circuits.." When you read and apply this to a panel when you have a mix of power and control circuits, the rational of not having short circuit ratings on control circuit devices becomes clearer.

UL 508A SB4.2.1 states "All power circuit components, including disconnect switches, branch circuit protection devices, branch circuit fuse holders, load controllers, motor overload relays, terminal blocks, and bus bars, shall have a short circuit current rating expressed in amperes or kiloamperes and voltage."

UL 508A does not require SCCR for control devices.

The UL 508A lists the definitions of a control circuit (2.11) and the power circuit (2.38).

SB3.2.1 addresses the over current protection of the control circuits tapped from the feeder circuit. Here is where UL 508A discusses the protection of the common control circuit, and the primary of a control transformer or power supply. It also addresses how that branch circuit protection fits into the determination of branch circuit current rating in SB4.4.1 and SB4.4.4(a) (Determination of the overall short circuit rating of a panel).