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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. This rating is used to determine compliance with the National Electric Code (NEC). The SCCR of equipment must be no less than the Available Fault Current (AFC). The AFC is the maximum amount of unwanted current that will flow on the grounded metal of the equipment in the event of a fault.
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What You'll Learn
- SCCR is a rating representing the maximum short-circuit current a component can withstand
- It determines compliance with NEC 110.10, requiring SCCR labelling on panels and assemblies
- SCCR is calculated by examining the maximum ratings of devices connected to branch circuits
- The device with the lowest rating becomes the limiting factor
- Mersen High-Speed Class J fuses are recommended for the best protection of electrical components
SCCR is a rating representing the maximum short-circuit current a component can withstand
Short Circuit Current Rating (SCCR) is a rating assigned to components and assemblies of electrical equipment. It represents the maximum amount of short-circuit current that a component or assembly can withstand without experiencing damage or failure. In other words, it is the equipment's ability to withstand high levels of current that may occur during a short circuit or other fault.
The SCCR is typically measured in amps and is used to determine the equipment's compliance with safety standards, such as the National Electrical Code (NEC). For example, NEC section 408.6 states that switchboards, switchgear, and panel boards must have an SCCR rating not less than the available fault current. This ensures that electrical panels and equipment can handle the high currents that may result from a short circuit or ground fault.
The SCCR rating is an important consideration in electrical design and equipment selection. It helps ensure that the equipment can safely operate within the electrical system and protect against potential hazards. The SCCR rating of a motor control system, for instance, is determined by evaluating the maximum ratings of the individual devices connected to the branch circuits. The device with the lowest rating becomes the limiting factor for the entire system.
Fuses are often used in conjunction with SCCR ratings to provide protection against short circuits. The primary role of a fuse is to prevent equipment fires by limiting the current during a fault. However, it is important to select the appropriate fuse size and type to ensure compatibility with the SCCR rating of the equipment. Maximum fuse sizing is typically dictated by the National Electric Code and standards set by organizations like Underwriters Laboratories (UL).
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It determines compliance with NEC 110.10, requiring SCCR labelling on panels and assemblies
The National Electric Code (NEC) defines the Short Circuit Current Rating (SCCR) as the "prospective symmetrical fault current at a nominal voltage to which an apparatus or system can be connected without sustaining damage exceeding defined acceptance criteria". In other words, it is the maximum level of short-circuit current that a component or assembly can withstand.
SCCR labelling is required on all panels and assemblies to ensure compliance with NEC 110.10. This label allows for the SCCR of the equipment to be easily compared with the maximum available fault current. The NEC requires that the labels are able to withstand the environment in which they are located and are placed on the equipment by the manufacturer.
The addition of SCCR nomenclature was to clarify that, for equipment with electrical power devices inside, the interrupting capacity (IC) rating of the main protective device alone is not enough, and the entire power circuit must be evaluated. If equipment already has an IC rating, then the SCCR is implied. For example, a panelboard, switchboard, or fused disconnect with an IC rating of 65kA implies that the equipment can withstand that much fault current.
To ensure compliance with NEC 110.10, it is important to have SCCR labelling on panels and assemblies, as well as to consider the environment in which the labels are placed.
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SCCR is calculated by examining the maximum ratings of devices connected to branch circuits
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 calculated by examining the maximum ratings of devices connected to branch circuits.
The branch circuits must have an SCCR equal to or higher than the let-through current of the feeder circuit. If they do not, the overall rating for the panel is the lower rating of the panel or the branch circuit.
To determine the SCCR, one must first identify the SCCR for the components and then determine whether feeder-circuit components, such as circuit-protective devices like fuses, limit the fault current. Circuit breakers must be marked "Current Limiting" to use SB4.3.2. The breaker let-through current will not exceed a defined value.
If the devices have a lower SCCR than the interrupt capacity of the circuit breaker, the SCCR for this circuit is the lower value. The maximum let-through for a circuit breaker is determined by the manufacturer. For fuses, it is determined by a standard, and Table SB4.2 can be used to obtain the necessary values.
When determining the SCCR for UL Listed industrial machinery, UL 508A Supplement SB would be the method used to determine the SCCR, and NFPA 79 is the standard/guide for designing and building the industrial machine.
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The device with the lowest rating becomes the limiting factor
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. This rating is used to determine compliance with NEC 110.10. SCCR labelling is required on all panels and assemblies.
The SCCR for the control panel is determined by the lowest SCCR value for any component or branch circuit. This means that the device with the lowest rating becomes the limiting factor. In other words, the device with the lowest rating determines the overall SCCR of the control panel.
The SCCR rating of the electrical panel must be equal to or greater than the available fault current determined. If the available short-circuit current supplied to the panel is higher than the SCCR rating marked on the rating label of the panel, installation of the panel is prohibited by NEC 670.5.
In general, on LV circuits, a single protective device protects against all levels of current, from the overload threshold to the maximum rated short-circuit current-breaking capability of the device. The protection device should be able to operate in a maximum time to ensure people and circuit safety for all short-circuit currents or fault currents that may occur.
The temperature rating related to the ampacity of a conductor must not surpass the lowest temperature rating of any connected termination, conductor, or device. This means that the device with the lowest temperature rating becomes the limiting factor for the overall temperature rating of the system.
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Mersen High-Speed Class J fuses are recommended for the best protection of electrical components
Mersen is an international industrial company that offers a wide range of circuit protection products. Their High-Speed Class J fuses are recommended for the best protection of electrical components.
Mersen's HSJ Class J High-Speed Fuses are designed to protect electrical components from short circuits. Short Circuit Current Rating (SCCR) is a measure of the maximum short-circuit current that a component or assembly can withstand. A 100kA SCCR is significant for meeting safety and insurance requirements, particularly in low-voltage operations where personnel work near live equipment.
Mersen's fuses are designed to provide protection in such scenarios. Their HP15NH photovoltaic (PV) fuse series is engineered to protect photovoltaic systems. The Helio-Protection® HP15NH fuse links safeguard cables in a PV group of chains during a short circuit in a panel. These fuses comply with IEC 60269-6 and UL 2579 PV standards and are available with various mounting options.
Additionally, Mersen's NH gBat fuse series is specifically designed for battery system protection. These fuses offer full-range protection, including small overcurrents and DC fault currents up to 150kA. The NH gBat series complies with the IEC 60269-7 standard for battery protection and is available in different sizes and voltage ratings.
Mersen's expertise in energy efficiency and thermal control of high-temperature industrial processes, along with their rigorous selection of raw materials, makes them a trusted provider of circuit protection solutions. Their Class J fuses, including the HSJ High-Speed Fuses, are recommended for safeguarding electrical components, ensuring compliance with safety standards, and providing reliable protection against short circuits.
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Frequently asked questions
SCCR stands for Short Circuit Current Rating.
The SCCR is the maximum amount of Root-Mean-Squared (RMS) current an electrical component can handle when using an overcurrent protection device, such as a fuse.
The SCCR of a motor control system is determined by examining the maximum ratings of the individual devices connected to the branch circuits. The device with the lowest rating becomes the limiting factor.
