Protect your equipment. Ensure compliance. Prevent catastrophic failure.
What is SCCR?
Short-Circuit Current Rating (SCCR) defines the maximum fault current a control panel can safely withstand without causing fire, explosion, or extensive damage. It’s expressed in kiloamperes (kA) and must meet or exceed the available fault current at the installation point.
Why SCCR Matters
Safety First
An underrated panel exposed to high fault current can fail violently—putting personnel and equipment at serious risk.
Code Compliance
Standards like NFPA 70 (National Electrical Code) and UL 508A require proper SCCR marking and verification for industrial control panels.
Avoid Costly Rework
If a panel’s SCCR is lower than the available fault current, it may fail inspection—leading to redesigns, delays, and added cost.
How SCCR is Determined
SCCR is based on the lowest-rated component within the power circuit—unless specific tested combinations allow for higher ratings.
Key factors include:
- Overcurrent Protection Devices (OCPDs)
Fuses and circuit breakers can significantly influence overall SCCR when properly selected. - Component Ratings
Contactors, motor starters, terminal blocks, and drives all have individual SCCRs. - Tested Combinations
Using manufacturer-tested combinations (per UL 508A Supplement SB) can increase the panel’s overall SCCR.
Common Pitfalls
Weakest-Link Limitation
A single low-rated component can reduce the entire panel’s SCCR.
Ignoring Available Fault Current
Failing to calculate or verify available fault current at the installation site leads to mismatches.
Improper Component Pairing
Not all combinations of breakers, fuses, and components are rated to work together at higher fault levels.
Using current-limiting devices or UL-tested component combinations can allow a control panel’s SCCR to exceed the rating of its lowest-rated individual component. A component SCCR applies only to an individual device, while a panel SCCR represents the overall short-circuit withstand rating of the entire assembled control panel under specified conditions.
How to Increase SCCR
Use Current-Limiting Fuses
These can dramatically raise the effective SCCR by reducing let-through energy during a fault.
Select High-SCCR Components
Choose contactors, drives, and terminals with higher withstand ratings.
Leverage Tested Assemblies
Follow UL 508A Supplement SB guidelines for approved component combinations.
Optimize Circuit Design
Segment circuits or add protective devices to isolate and limit fault exposure.
Best Practices
- Verify available fault current early in the design phase
- Match or exceed SCCR across all components
- Clearly label panel SCCR per code requirements
- Document calculations and component ratings for inspection
SCCR isn’t just a specification—it’s a critical safeguard. Properly rated control panels protect people, ensure compliance, and prevent costly failures.
