Circuit Breaker Ratings and Electrical Protection

In summary, the conversation discusses the process of determining the required short circuit current rating of a circuit breaker for a standard commercial installation. The speaker has referred to the Schneider Electric catalog for guidance and is also concerned about other protection terminology and requirements. They have also attempted to go through the Australian Standards but are seeking a more concise answer. A suggestion is made to check for the "subtransient reactance" number of the transformer to determine its short circuit performance.
  • #1
MetroEngineer
3
0
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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  • #2
see if there's a number for 'subtransient reactance' on that transformer.

that should lead you to its short circuit performance.
 

1. What is a circuit breaker rating?

A circuit breaker rating is a measure of the maximum current that a circuit breaker can safely handle without tripping. It is typically expressed in amperes (A) and is determined by the design and construction of the circuit breaker.

2. Why is it important to have the right circuit breaker rating?

Having the right circuit breaker rating is important because it ensures that the circuit breaker can handle the normal current load of the circuit without tripping. If the rating is too low, the circuit breaker may trip frequently, causing inconvenience and potential damage to electrical equipment. If the rating is too high, the circuit breaker may not trip when it should, posing a safety hazard.

3. What factors determine the circuit breaker rating?

The circuit breaker rating is determined by the type and size of the circuit, the type of load (e.g. resistive, inductive, capacitive), and the ambient temperature. In general, larger circuits and higher ambient temperatures require higher circuit breaker ratings.

4. Can a circuit breaker rating be increased?

No, a circuit breaker rating cannot be increased. The rating is determined by the design and construction of the circuit breaker and cannot be changed. If a higher rating is needed, a different circuit breaker with a higher rating must be installed.

5. How does a circuit breaker protect against electrical hazards?

A circuit breaker protects against electrical hazards by automatically opening the circuit when it detects an overload or short circuit. This prevents excessive current from flowing through the circuit and potentially causing damage or starting a fire. Additionally, some circuit breakers have built-in features such as ground fault protection to further enhance safety.

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