AIC and available fault current

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Jennabob

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Sequim, WA
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Electrical Admin
Hi All,
I am a new Electrical Admin. I have very limited practical experience, however passed the Exam with flying colors including a 90% on the calcs. However, that is not helping me at all as I am very familiar and comfortable with load and motor calcs but nothing else (learning everyday). So, please excuse my ignorance. My EC sent me the following from the POCO. Below is the only info I have. I'm not sure what they need of me or what calculation to use given the very limited info. Any help would be greatly appreciated. Thanks!

First email: The AIC for the service at 825 Georgiana St. is 3,172A at the top of the weatherhead.
Second email (from another guy at POCO): Don't forget to apply the available fault current on the panel.
 
Dennis Alwon

Dennis Alwon

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Yeah that is something we don't learn in the field or at school. Fault current is usually calculated by an engineer but maybe someone here can help more. I believe Mike Holt has a free fault current calculator
 
T

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
Jennabob said:
Hi All,
I am a new Electrical Admin. I have very limited practical experience, however passed the Exam with flying colors including a 90% on the calcs. However, that is not helping me at all as I am very familiar and comfortable with load and motor calcs but nothing else (learning everyday). So, please excuse my ignorance. My EC sent me the following from the POCO. Below is the only info I have. I'm not sure what they need of me or what calculation to use given the very limited info. Any help would be greatly appreciated. Thanks!

First email: The AIC for the service at 825 Georgiana St. is 3,172A at the top of the weatherhead.
Second email (from another guy at POCO): Don't forget to apply the available fault current on the panel.
Click to expand...
The POCO is using the wrong term. AIC (amps interrupting current) is the rating of a breaker, fuse, etc. in amps that it is capable of opening under a short circuit current. It appears to me they mean they have 3172 amps of available fault current at that point. A Breaker installed at that point in the system will then need an AIC rating of at least that value. So you would use a 10K rated breaker as that is standard minimum in most cases.
Field marking of available fault current for service equipment is required. See 110.24 for details. Note this would not apply to a dwelling unit.
There are other areas of the code that require available fault current labeling as well. But remember, even if labeling is not required the equipment must still be rated for the fault current that is available at the point in a system that it is installed.
I would suggest you get the free Android/Apple fault current app from Bussmann as it is a valuable tool. You can practice with it and learn a lot by trying various scenarios. Fault current has become sort of a hot button issue in recent years in the code and you should learn as much as possible to understand the concepts. Also note that available fault current is not the same thing as incident energy as many erroneously think.
 
augie47

augie47

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Tennessee
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State Electrical Inspector (Retired)
Last edited:
Jraef

Jraef

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Location
San Francisco Bay Area, CA, USA
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Electrical Engineer
texie said:
The POCO is using the wrong term. AIC (amps interrupting current) is the rating of a breaker, fuse, etc. in amps that it is capable of opening under a short circuit current. It appears to me they mean they have 3172 amps of available fault current at that point. …
Click to expand...
Agree, but maybe they meant AFC (Available Fault Current), not AIC.

I don’t know of any panels or gear rated for less than 10kA, even untested devices are good fir 5kA, so you (OP) should be fine.
 
G

gh0st

Member
Location
California
Occupation
Designer
I would first question at what point in the distribution do you need to run this calc?
If you're replacing the service, then you can go with 3,172 available fault at the utility primary for your calculations. I agree with Jraef, regarding standard equipment ratings.
If you're adding a breaker to the main panel, that OCPD should have the same (max) AIC rating at the equipment it is being installed in.
If you're performing work downstream of the service, there are other contributing elements (ie. motors) that will affect the required AIC ratings.
 
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