Molly Ayala
Short-Circuit Current Rating (SCCR) is a rating on components and assemblies representing the maximum level of short-circuit current that a component or assembly can withstand. SCCR is often used interchangeably with Ampere Interrupting Capacity (AIC), but they are not the same. While AIC applies to protective interrupting devices such as circuit breakers and fuses, SCCR looks at the product as a whole and what it can withstand. SCCR is an important consideration for electrical safety, as it helps prevent equipment from being located in an electrical system where the available fault current is greater than what the equipment can handle.
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What You'll Learn
SCCR stands for Short-Circuit Current Rating
SCCR is an important consideration for electrical safety. Both the NEC and OSHA requirements for SCCR prohibit having any equipment located within an electrical system where the available fault current exceeds the equipment's capacity. This applies to new installations and equipment moved within or between facilities. Overcurrent protective devices, such as fuses and circuit breakers, must have suitable interrupting ratings for the available fault current.
It is important to note that SCCR considers the product as a whole and what it can withstand. It describes the maximum fault current that a product can safely withstand or the maximum available fault current that the product may be safely connected to. For example, a meter socket with an SCCR of 10K should be able to withstand a three-cycle (1/20 of a second) surge of up to 10,000 Amps without breaking down or posing immediate danger.
To ensure compliance with SCCR requirements, it is necessary to know the available fault current in the facility where equipment is installed. Software programs and mobile applications are available to calculate fault current levels and ensure compliance with NEC and OSHA SCCR requirements. Additionally, UL Listed industrial machinery uses UL 508A Supplement SB to determine SCCR, and NFPA 79 is the standard guide for designing and building such machinery.
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SCCR is calculated using complex methods
SCCR, or Short-Circuit Current Rating, is a critical specification when designing industrial control panels. While determining the SCCR does not involve calculations per se, it is a complex process that requires a series of steps to be followed.
Firstly, the SCCR of each component or combination of components in the power circuit must be determined. This information is usually found on the component label or its instruction manual. For unmarked components, the Assumed Maximum Short Circuit Current Rating for Unmarked Components, Table SB4.1 in the UL 508A Standard, can be used.
Secondly, it is necessary to identify whether feeder circuit components limit fault current. This includes circuit-protective devices such as fuses or circuit breakers.
The third step is to determine the overall short-circuit current rating for the industrial control panel. The panel SCCR is the smallest branch circuit SCCR.
Finally, the SCCR marking must be listed on the control panel nameplate.
Additionally, when determining the SCCR for machinery, it is important to consider the available fault current at the line terminals of each machine supply circuit disconnecting means. This is to ensure that the control panel has an adequate short-circuit current rating. If a machine has multiple industrial control panels, each panel must have its own nameplate that includes the SCCR.
Furthermore, when selecting a current-limiting fuse or circuit breaker, it is critical to ensure that it limits the peak current to a value less than or equal to the SCCRs of all panels supplied by the main panel.
While there are software programs and tools available to simplify SCCR calculations, the process can still be complex, particularly when considering the specific requirements and standards that must be met to ensure safety and compliance.
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SCCR and AIC are different
Short-Circuit Current Rating (SCCR) and Ampere Interrupting Capacity (AIC) are two different electrical terms that are often confused with each other. SCCR is the maximum fault current that a product can safely withstand without breaking down or causing immediate danger. For example, a meter socket with an SCCR of 10K should be able to withstand a three-cycle (1/20 of a second) surge of 10,000 Amps without any issues.
SCCR is calculated using complex methods, and it is crucial for ensuring the safety of electrical systems. Overcurrent protective devices like fuses and circuit breakers must have suitable interrupting ratings to limit the available fault current and prevent it from exceeding the equipment's SCCR.
On the other hand, AIC, also known as Available Interrupting Current or Ampere Interrupting Rating, is a rating given to protective devices such as circuit breakers and fuses. It describes the maximum fault current that these protective devices can safely clear without welding closed or causing damage to equipment or personnel. For instance, a device rated 10K AIC can interrupt current up to 10,000 Amps without shorting to ground or exposing live parts.
While SCCR focuses on the product's ability to withstand a fault current, AIC focuses on the protective device's ability to interrupt the fault current safely. Some metering products may have both an SCCR and a different AIC rating, with the AIC rating applying to the internal means of disconnect, such as a breaker or fuse, within the product.
It is important to understand the distinction between SCCR and AIC to ensure proper electrical safety and compliance with industry standards and regulations.
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SCCR is about safety
SCCR, or Short-Circuit Current Rating, is a critical aspect of electrical safety in various contexts, from industrial machinery to electrical panels and installations. It refers to the maximum short-circuit current that a component, assembly, or system can withstand without sustaining damage or causing immediate danger. This rating is essential for ensuring compliance with safety standards and regulations, such as those outlined by the National Electrical Code (NEC) and the Occupational Safety and Health Administration (OSHA).
The NEC and OSHA requirements for SCCR are designed to prevent equipment from being exposed to fault currents higher than they can handle. This rule applies to newly installed equipment and equipment moved within or between facilities. Overcurrent protective devices, such as fuses and circuit breakers, play a crucial role in this regard. They must have suitable interrupting ratings to limit the fault current and protect the equipment.
While AIC (Ampere Interrupting Capacity or Available Interrupting Current) specifically addresses the capacity of protective devices like circuit breakers and fuses to interrupt or disconnect in the event of surges, SCCR focuses on the product as a whole. SCCR determines the maximum fault current a product can safely withstand. For example, a meter socket with an SCCR of 10k should be able to handle a short-duration surge of up to 10,000 Amps without failing or posing an immediate threat.
Compliance with SCCR requirements is essential for maintaining safety in electrical systems and installations. Properly calculating and adhering to SCCR values help prevent equipment damage, fires, and electrical hazards that can endanger personnel and property. This is particularly crucial in industrial settings where machinery and electrical equipment are prevalent. By ensuring that equipment can withstand potential fault currents, the risk of accidents and injuries is significantly reduced.
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SCCR compliance can be ensured with software
SCCR stands for Short-Circuit Current Rating. It is a critical measure in electrical systems, as it ensures that equipment can withstand the available fault current in the event of a short circuit. Non-compliance with SCCR requirements can lead to safety hazards and costly shutdowns and delays.
To ensure SCCR compliance, electrical systems must adhere to specific standards and regulations, such as the National Electrical Code (NEC) and Occupational Safety and Health Administration (OSHA) requirements. These regulations prohibit equipment from being located where the available fault current exceeds the equipment's capacity. This applies to new installations and equipment moved within facilities.
Compliance software has emerged as a valuable tool to ensure SCCR compliance. One prominent example is the Cooper Bussmann OSCAR (Online Short-Circuit Current Rating) software, which helps facilities comply with electrical industry standards for determining the SCCR of industrial control panel assemblies. This software offers a comprehensive database of over 50,000 online part numbers, enabling users to accurately determine the SCCR of their assemblies. OSCAR also allows users to enter specialised component rating information for devices not found in its database, ensuring flexibility and customisation.
The OSCAR software simplifies the complex process of calculating SCCR, reducing the risk of non-compliance. It guides users through entering an electrical panel's components, calculating the equipment SCCR, and providing detailed documentation. This user-friendly approach ensures that facilities can meet the marking requirements specified by the 2017 NEC and UL 508A Supplement SB. Additionally, OSCAR provides access to a portfolio of circuit protection devices, helping to address any weak links in the system.
Another useful tool for ensuring SCCR compliance is the Bussmann series FC2 Available Fault Current Calculator, offered by Eaton. This online and mobile app enables users to easily calculate fault current levels and generate NEC-compliant labels and diagrams. Knowing the available fault current is crucial for complying with NEC and OSHA SCCR requirements, and this tool simplifies the process.
In conclusion, SCCR compliance is essential for the safety and proper functioning of electrical systems. By utilising software tools like OSCAR and the FC2 Available Fault Current Calculator, facilities can ensure compliance, mitigate risks, and protect their equipment and personnel from the dangers of short circuits. These software solutions streamline the complex calculations and documentation required for SCCR compliance, making them invaluable resources for electrical system management.
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Frequently asked questions
SCCR stands for Short-Circuit Current Rating.
A Short-Circuit Current Rating is a rating on components and assemblies representing the maximum level of short-circuit current that a component or assembly can withstand.
AIC stands for Ampere Interrupting Capacity or Available Interrupting Current. AIC applies to protective interrupting devices such as circuit breakers and fuses, whereas SCCR looks at the product as a whole and what it can withstand.
The calculation method is complex. It requires the demonstration that the downstream circuit breaker remains passive during the short-circuit interruption period of the line-side protective device.
The SCCR Protection Suite is an online application that provides access to a comprehensive product portfolio of circuit protection and wiring distribution/termination/switching devices and their component SCCRs.
