Industrial Control Panel SCCR (UL 508A)
The short-circuit current rating of an industrial control panel by the UL 508A weakest-link method.
Example
You enter
- Component SCCRs (kA, comma or space separated) 65, 5, 5, 10
- Available fault current (kA) 22
You get
- Panel SCCR (weakest link) 5
Checked against published worked examples from: UL 508A Supplement SB / NEC 409.110.
Details, formula, and sources
ScopeThe panel SCCR is the LOWEST of its power-circuit components' individual ratings (and the feeder OCPD interrupting rating), not the main breaker -- one 5 kA contactor caps the whole panel. Checked against the available fault per NEC 409.110. A current-limiting fuse can raise a weak component's combination rating.
Formula or tablepanel_sccr = min(component SCCRs, feeder OCPD interrupting rating); compliant when panel_sccr >= available_fault.
Source and editionThe UL 508A Supplement SB industrial-control-panel short-circuit current rating (weakest-link method), with NEC 409.110 / 110.10, by name.
Free accessThe weakest-link SCCR method is defined in UL 508A Supplement SB; NEC 409.110 is available through NFPA free online read-only access.
What governsEstimate. AHJ and licensed professional govern.
API field namescomponent_sccrs_ka, available_fault_ka, panel_sccr_ka
- Weakest link panel SCCR = min of the component SCCRs and the feeder OCPD interrupting ratingUL 508A Supplement SB
- Combination ratings a listed current-limiting device can raise a weak component's combination SCCR through its let-throughUL 508A Supplement SB