Siemens NEC Article 409 - Overview of Supplement SB from the UL 508 A Standard

Short-circuit current rating (SCCR) of industrial control panels
Reference Manual, 06/2013, A5E31896849002A/RS-AA/001
11
Overview of Supplement SB from the UL 508A
standard
3
Components in the power circuit
UL508A is the safety standard for industrial control panels.
NEC Article 409 references UL508A Supplement SB as an approved method for determining
the SCCR of an industrial control panel. The specific method is outlined in Section SB4.
The SCCR of the control panel is based on the SCCR of each component in the power
circuit. The component with the lowest SCCR defines the SCCR of the entire panel.
Paragraph SB4.2.1 and Table SB4.1 list the following components as part of the power
circuit:
Disconnect switches
Supplementary protectors
Branch circuit protective devices
Busbars
Fuseholders
Current meters
Load controllers
Current shunts
Motor overload relays
Switch units
Receptacles Terminal blocks or power distribution
blocks
Paragraph SB3.2.1 states that the primary short-circuit protective device for the control
circuit is also included in the calculation for the SCCR for the power circuit. Therefore, the
SCCR of the overcurrent protective devices (except for supplementary protectors recognized
according to UL1077 or sets of supplemental fuses recognized according to UL248-13) are
included in calculation of the SCCR of the control panel. Control circuit components on the
load side of these devices are not included in calculation of the SCCR.