In electrical terms, ICC often refers to the Rated Conditional Short-Circuit Current.
Specifically, according to EN 61439-1, Icc is the rated conditional short-circuit current of a circuit of an ASSEMBLY. This value, specified by the manufacturer, indicates the level of short-circuit current that a particular circuit within an electrical assembly can satisfactorily withstand when protected by a specific current-limiting Short-Circuit Protective Device (SCPD) also specified by the manufacturer. The withstand capability is for the operating time of that protective device.
Understanding Rated Conditional Short-Circuit Current (Icc)
The concept of ICC is crucial for ensuring the safety and reliability of electrical installations, particularly within low-voltage switchgear and controlgear assemblies governed by standards like EN 61439.
Here's a breakdown of the key elements:
- Rated Value: This is a maximum current level determined by the manufacturer.
- Conditional: The ability to withstand this current is conditional on the presence and correct operation of a specific current-limiting protective device (SCPD).
- Short-Circuit Current: This is the abnormally high current that flows during a fault condition, like a short circuit.
- Assembly: This term refers to a combination of one or more low-voltage switchgear and controlgear devices with associated control, measurement, signalling, protective, regulating equipment, interconnections, and structural parts, intended for electrical power distribution and control.
Essentially, Icc tells you that if a short circuit occurs, the circuit within the assembly is designed to survive the event provided the specified protective device clears the fault quickly enough, limiting the energy let-through.
Why is ICC Important?
Determining and specifying the ICC is vital for several reasons:
- Safety: Ensures that in the event of a short circuit, the assembly components do not catastrophically fail, causing fire or injury.
- Equipment Protection: Protects the equipment within the assembly from damage during a fault.
- Coordination: Requires careful coordination between the assembly's design, the specific circuit, and the selected protective device (SCPD).
- Compliance: Adherence to standards like EN 61439-1 which mandate the determination and verification of this rating.
Practical Implications
For engineers and technicians working with electrical assemblies:
- Always check the manufacturer's declared ICC rating for a specific assembly or circuit.
- Ensure that the specified SCPD is installed and correctly rated.
- Understand that the assembly's short-circuit withstand capability relies heavily on the performance of the upstream protection.
- Do not replace the specified SCPD with a device that has different characteristics (especially higher let-through energy) unless verified by the manufacturer.
| Term | Definition (Based on EN 61439-1) |
|---|---|
| Icc (Rated Conditional Short-Circuit Current) | The value of short-circuit current, specified by the manufacturer, which a circuit of an ASSEMBLY, protected by a current limiting SCPD specified by the manufacturer, can withstand satisfactorily for the operating time of the device. |
| ASSEMBLY | A combination of switchgear, controlgear, and related equipment. |
| SCPD | Short-Circuit Protective Device (e.g., fuse, circuit breaker). |
Understanding ICC is fundamental for anyone involved in designing, installing, or maintaining low-voltage electrical assemblies to ensure safety and compliance with relevant standards.
