Circuit Breaker Ratings and Electrical Protection

AI Thread Summary
To determine the required short circuit current rating of a circuit breaker for a standard commercial installation, it is essential to reference the upstream short-circuit current information, which may be available through Australian standards for 22kV/415V transformers. The discussion highlights the importance of understanding various protection terminologies such as Earth fault loop impedance, overload current, and RCDs. Users are encouraged to consult the Schneider Electric catalog for guidance on short-circuit current determination using cable data. Additionally, the concept of cascading and enhanced discrimination is mentioned as a means of backup protection. Overall, a thorough understanding of these factors is crucial for ensuring electrical safety and compliance.
MetroEngineer
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Hi,

I am student electrical engineer and I should probably know this stuff but I am trying to work out how to determine the required short circuit current rating of circuit breaker, I have seen in the Schneider Electric catalog 'determination of short-circuit current" using cable data and upstream short-circuit current information (which I can't find - I am assuming since this a standard commercial installation there is a Australian standard upstream SC rating for 22kV/415V transformer), there is also cascading(backup) and enhanced discirmination. I'm also concerned with all the 'other' protection terminology and requirements, Earth fault loop impedance, overload current, disconnection times, RCDs, abnormal voltages, equipotential bonding etc.

I have tried to go through the Australian Standards to determine how to determine the ratings for a standard commercial installation, but was hoping someone could enlighten me with a more succinct answer please!
 
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see if there's a number for 'subtransient reactance' on that transformer.

that should lead you to its short circuit performance.
 
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