AIC Ratings
- Thread starter eroberts
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What does the manufacturer's cut sheet say? Or even the breaker?
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- Wisconsin
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- PE (Retired) - Power Systems
eroberts said:
Your question is poorly worded.
Do you want to know the short circuit current available from your 150KVA transformer? If so you will need to know the %Z of the unit and preferably the line side available current.
Or, do you want to know the AIC of a general breaker? There are no standard AIC ratings of breakers based only on their ampacity and voltage.
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- Wisconsin
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- PE (Retired) - Power Systems
You have not described a circuit breaker. You have described a transformer. Are you trying to specify a secondary main breaker?
The general AIC rating of circuit breakers is 5kA unless they are listed for a higher amount.
The general AIC rating of circuit breakers is 5kA unless they are listed for a higher amount.
eroberts said:
According to Cooper Bussman, a 3 phase, 150 KVA xfmr with a 120/208 volt secondary and an impedance of 1.07% will have an available fault current of 43,237 amps. Keep in mind this is the AIC at the secondary terminals of the transformer. As the distance increases from the utility xfmr to the service disconnecting means, the fault current decreases.
The publication "SPD - Selecting Protective Devices Based On The 2005 NEC", by Cooper Bussman is an increadible resourse for calculating AIC.
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- San Francisco Bay Area, CA, USA
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- Electrical Engineer
Every breaker manufacturer is different. Most "Normal" off the shelf molded case breakers are anywhere from 14 - 65kAIC depending on brand and frame size. Most manufacturers also have 2 or 3 "levels" of breaker ratings available, calling them out by various terms such as "HIC" for High Interrupting Capacity, or even UHIC for Ultra High... Eaton (old Westinghouse) for instance has, for a 630A Frame, 400A trip breaker as you would likely use, 2 ratings available for 220V; 65kAIC and 100kAIC. Siemens Sentron breakers come 65, 100 or 200kAIC. ABB breakers are 65, 100 and 150kAIC for their "Normal", "High" and "Extra High" versions.
So basically you get what you pay for. With roughly 42k available in your case (give or take a few thousand), a 65kAIC breaker is going to be fine, just make sure it says that on the breaker itself.
So basically you get what you pay for. With roughly 42k available in your case (give or take a few thousand), a 65kAIC breaker is going to be fine, just make sure it says that on the breaker itself.
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