Fault Rating is an extremely important element when devising a system, it is the maximum current your switchgear can withstand under short circuit fault conditions. This can be calculated by

 

KA = (Transformer KVA Rating / (√3 x Volts ) / Transformer Impedance

(400V is typically the worst case application for 3 phase systems)

 

Example,

Isc = ((100,000 / 693) / 0.06) = 24,050 KA fault rating.

 

 This is typically supported by a Short Circuit Test Certificate (Expand-Click Me), typically known as ASTA or KEMA Certificate.
A fault rating certificate is awarded to clarify that the switchgear will still function under a given fault. Typically,

 

- 36KA for 1 Second

- 50KA for 1 Second or 50KA for 3 Seconds

- 70KA for 1 Second or 70KA for 3 Seconds

- 80KA for 1 Second or 80KA for 3 Seconds

- 100KA for 1 Second or 100KA for 3 Seconds

 

Your Switchgear needs to have this certificate to ensure it can take the maximum fault current supplied by the transformer (& other network incoming supplies if at all running in sync), this to ensure that the system can withstand the maximum fault levels that can be supplied at any one time by your network. Therefore if a fault was to occur the Switchgear would in fact still be functional afterward, however, noting that this is the essential test certificate for any Switchgear construction assembly. Quick point of advice when reviewing this certificate, always check the busbar ratings of your switchgear and the given certificate, ensuring this matches the given design throughout the complete panel to ensure the complete busbar is certificated to you detailed fault rating. This doesn't limit it to the same busbar rating, however, ensures that the complete busbar is rated to the maximum fault rating.