Short Circuit Withstand Testing

What is a Short Circuit?

Short Circuit Withstand testing is an aspect of 60439 Type Testing Assemblies or 61439 Verification, this is designed to ensure that the complete switchboard assembly can withstand the specified fault levels dictated by the network.

A short circuit is a low resistance connection between two or more conductors, it is essentially exactly what it says on the tin, a short between phases, commonly known as a 'dead short' referring to zero resistance which results in increased current flow to the designated Short Circuit, hence the requirement for every switchboard to have the certification that is relevant to the product

The most common ratings detailed below:

  • 25kA for 1 Second

  • 36kA for 1 Second

  • 50kA for 1 Second

  • 70kA for 1 Second

  • 80kA for 1 Second

  • 100kA for 1 Second

 

What Switchgear Manufacturers must do?

Simply, every switchboard must have a 3 phase Short Circuit Withstand for the complete assembly and a PE certificate typically 60% of the 3 phase fault level. 

This test assuring that the fault withstand capability of the product is a statement of operation without failure to either personnel or equipment up to the detailed fault level, and therefore suitable after for further service,. 

How does it affect assemblies?

Short circuits produce extremely high temperatures and mechanical stress due to high power dissipation. This is commonly demonstrated when you are to 'google' short circuits you see items exploding, which obviously doesn't fit the application.

The mechanical stress that is generated due to opposing magnetic fields between shorted conductors can be measured in tons. Ensuring that the product components must not only be large enough (typically relating to busbar size) but also mechanically strong enough to ensure prevention from movement and distortion.

The temperature rise that is generated due to the let-through energy of the fault must be absorbed by the product, of which to ensure to not cause damage to any part of the product functionality, ensuring the components are large enough to absorb the heat created which can commonly cause arc welding temperatures and melting upon failure which is commonly resulted in the physical welding of components.

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