Short-Circuit Current Rating (SCCR) is the maximum fault current an industrial control panel can safely withstand. NEC Article 409.110 requires the marked SCCR to meet or exceed the available fault current at the installation point.
A short circuit creates an unintended low-resistance current path. The resulting fault current can reach 10,000 to 200,000+ amperes, vaporizing conductors and causing arc flash events in milliseconds. A panel with a 10 kA SCCR installed on a system with 50 kA available fault current is a safety hazard and a code violation.
A panel's overall SCCR equals the SCCR of its weakest component in the power circuit. If a panel contains a 65 kA main breaker, a 50 kA motor starter, and a 10 kA supplementary protector on a control circuit, the panel's SCCR is 10 kA. The calculation must account for every component including control power transformers, power supplies, pilot devices, and terminal blocks.
Supplement SB provides three methods:
| Component Type | Default SCCR |
|---|---|
| Industrial control equipment (UL 508) | 5 kA |
| Supplementary protectors (UL 1077) | 5 kA or marked rating |
| Power supplies | 5 kA |
| Terminal blocks | 10 kA |
| SCCR (kA) | Typical Application |
|---|---|
| 5 kA | Default for many control components; small isolated systems only |
| 10 kA | Light commercial, small machinery, panels far from service entrance |
| 22–25 kA | Standard commercial and light industrial |
| 50 kA | Heavy industrial, most manufacturing floor applications |
| 65 kA | Large industrial, panels near service entrance transformers |
| 100 kA | High-power industrial, utility-adjacent installations |
| 200 kA | Maximum rating with current-limiting fuses and tested combinations |
Class J, RK1, CC, and CF fuses clear faults in less than half a cycle, limiting let-through current. A branch circuit with a 5 kA component can achieve 100–200 kA SCCR when protected by the right current-limiting fuse.
Two components tested together under fault conditions may achieve a higher SCCR than either alone. A 5 kA motor starter might achieve 65 kA when protected by a specific Class J fuse — but only for that exact combination. Manufacturers publish tested combination tables (Eaton, Siemens, ABB, Rockwell, Schneider).
Some breakers are listed as current-limiting and reduce fault current to downstream components. Not all breakers are current-limiting — standard thermal-magnetic breakers typically do not reduce downstream SCCR.
| Installation | Typical Available Fault Current | Recommended Min SCCR |
|---|---|---|
| Small commercial (200A service) | 5–14 kA | 10–14 kA |
| Large commercial (400–800A) | 14–25 kA | 25 kA |
| Light industrial | 10–25 kA | 25 kA |
| Manufacturing floor | 25–65 kA | 50–65 kA |
| Heavy industrial | 50–100 kA | 65–100 kA |
| Utility / process plant | 65–200 kA | 100–200 kA |
Sterling Made performs SCCR calculations per UL 508A Supplement SB on every panel, documenting the methodology in a worksheet that ships with the panel. Contact us at 617-256-3460 or request a quote.