Short-circuit current of SPD disconnector is important

The question of whether short-circuit current is an important factor in the regulations for disconnectors installed before surge protective devices (SPDs) can be clearly answered as “yes” for the following reasons:

Regulatory and Technical Requirements

1. The role of SPD disconnector

• This device safely disconnects the SPD from the system when it fails or requires maintenance. This disconnector can be installed either internally or externally (External SPD Disconnector).

1. Short-circuit current and related standards

• According to representative KS C IEC 61643-11, KS C IEC 61643-12, and IEC 60364-5-53 regulations, SPD separators must have the ability to protect not only overcurrent (surge, fault, leakage, etc.) but also short-circuit current .

• In particular, the Disconnector installed before the SPD in the system must be able to withstand the **maximum short-circuit current (Isc)** that may flow through the SPD and circuit breaker, and must have the short-circuit withstanding rating (kA) specified by the SPD manufacturer or required by the relevant standards.

1. Selection criteria for SPD disconnectors

• The rated short-circuit breaking current capacity (kA) of the separator , i.e. the capacity that can withstand a system short-circuit, must be taken into consideration, and this value must be determined by calculating the actual short-circuit current around the installation location of the SPD, etc.

• Typically, SPD external isolators are required to have the following ratings:

thermal protection

Over-current and short-circuit protection

Surge impulse withstand

Convenience of maintenance, etc.

Real-world examples from standards/catalogs

• For external isolators specifically designed for SPDs used in practice, the “maximum short-circuit current (Isc)” rating is specified, and must be used in accordance with the system’s short-circuit current rating, such as 25kA .

• If the SPD Disconnector cannot withstand the short-circuit current of the system, serious secondary damage (fire, equipment damage, etc.) may occur to both the SPD and the system. Therefore, the short-circuit current rating must be considered and is required by regulations.

conclusion

In the regulations for disconnectors installed before surge protectors, “short-circuit current” is a very important factor and a key criterion that must be considered.

That is, the separator must have a rating that can block/withstand more than the expected short-circuit current of the system, and this must be clearly stated in all domestic and international standards, design guidelines, and practice catalogs.

The KS C IEC 61643-1 (IEC 61643-1) standard makes clear reference to short-circuit current in relation to the disconnector of SPD (surge protective device) .

The standard stipulates that:

• It states that “the overloaded (short-circuited) SPD must be able to withstand the power short-circuit current that may occur in actual service”, and short-circuit current testing of the internal or external separator of the SPD is also required in actual testing.

• In the test, the voltage-limiting components of the SPD (e.g., MOV, circuit breaker, etc.) are replaced with a copper block (dummy) to evaluate whether the entire SPD (i.e., including the disconnector) normally disconnects at the maximum short-circuit current Isc specified by the manufacturer .

• At this time, the disconnector must function properly to safely disconnect the SPD from the system in a short-circuit current situation without fire, explosion, or damage. Therefore, short-circuit current (Isc) is an item that must be tested and required by regulations.

• These tests and evaluations are adopted not only in IEC 61643-1 but also in domestic KS C IEC 61643-1.

Therefore, we can confirm that the short-circuit current related tests and safety requirements of SPD disconnectors are officially specified in KS C IEC 61643-1 .

Short-circuit current is one of the most important safety requirements for SPDs (including disconnectors).