Short Time Rating of Circuit Breaker Formula
The short time rating (STR) of a circuit breaker is the maximum current that the breaker can carry for a specified period of time without tripping. The STR is typically expressed in kiloamperes (kA) and the time period is typically expressed in seconds (s). The STR is important because it determines the maximum fault current that the breaker can withstand without tripping. If the fault current exceeds the STR, the breaker will trip, which will interrupt the flow of electricity and protect the circuit from damage. The STR is determined by the following factors: * The interrupting rating of the breaker * The type of fault * The duration of the fault The interrupting rating of the breaker is the maximum current that the breaker can interrupt without damage. The type of fault refers to the way in which the fault occurs. There are two types of faults: * Line-to-line faults * Line-to-ground faults The duration of the fault refers to the length of time that the fault occurs. The STR is calculated by multiplying the interrupting rating of the breaker by the factor for the type of fault and the duration of the fault. The following table shows the factors for different types of faults and durations: | Fault Type | Duration | Factor | |---|---|---| | Line-to-line | 0.5 s | 1.0 | | Line-to-line | 1.0 s | 1.2 | | Line-to-line | 3.0 s | 1.5 | | Line-to-ground | 0.5 s | 0.8 | | Line-to-ground | 1.0 s | 1.0 | | Line-to-ground | 3.0 s | 1.2 | The STR is an important safety factor to consider when selecting a circuit breaker. The breaker should have a STR that is greater than or equal to the maximum fault current that is likely to occur in the circuit. ## Example Let's say that we have a circuit breaker with an interrupting rating of 10 kA. We want to determine the STR for a line-to-line fault that lasts for 1.0 second. The factor for a line-to-line fault that lasts for 1.0 second is 1.2. So, the STR for this circuit breaker is 10 kA * 1.2 = 12 kA. This means that the circuit breaker can withstand a fault current of up to 12 kA for 1.0 second without tripping. ## Conclusion The short time rating of a circuit breaker is an important safety factor to consider when selecting a circuit breaker. The breaker should have a STR that is greater than or equal to the maximum fault current that is likely to occur in the circuit. ## References * [IEC 60898-1:2016, Circuit-breakers for ac circuits – Part 1: General rules](https://www.iec.ch/en/standards/standard/60898-1ed2.html)
Air Operated Circuit Breaker Terasaki Electric Ltd Short Modular
Example To Calculate Short Circuit Cur For Breaker Drf Engineering Services
Simple Method For Basic Short Circuit Cur Calculations
Determining Short Circuit Rating Of Breakers Peguru
Short Circuit Cur Duties Of Breakers And Fuses Part 1 Ec M
Iec 60909 Short Circuit In Easypower
Duty Cycle Of Circuit Breaker Operating Sequence
Electrical Motor Circuit Protection Water Well Journal
Maximum Available Fault Cur What Is It Rozel Arc Flash Stus Electrical Safety Training
Dc Component Of Asymmetrical Faults
Circuit Breaker Ratings Breaking Capacity Making
Defining Short Circuit Values For Breakers Abb
Short Circuit Rating Selection Criterion S For Breaker In Pv Plants
Circuit Breaker Operation Operating Tripping Time Electrical4u
Circuit Breaker Rating
Defining Short Circuit Values For Breakers Abb
Setting Of Overload Short Circuit Ground Fault Protection Mccb Part 1
Short Circuit Rating Selection Criterion S For Breaker In Pv Plants
Short Circuit Cur Rating Sccr Vs Available Fault Understanding The Maze And What S New For 2020 Jade Learning