TRansformer AIC

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augie47

augie47

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State Electrical Inspector (Retired)
I don't seem to have the charts I once had but I need to have some idea of the AIC av available from a 167 kva dry type transformer 480 -240/120 volt. I know it's impedance related but I don't have that info and at one time I had some charts that showed a "common" number which is all I need a present. Anyone ?
 
AIC is a term used only with protective devices that interrupt fault current. This is related to NEC 110.9.
SCCR is a term used with non protective devices. This is related to NEC 110.10


You are looking for the SCA (short circuit amps, or short circuit available) from your source.
The cheap and dirty method, for transformers, is to take the FLA and divide it by the impedance.

In your case of a 167kVA, 240V:
FLA = 695A
%Z = 1.9 (provides a worse case based on my local POCO)

SCA = 695/.019 = 36,579 = 37kA rounded

This means you need to specify devices rated for a minimum of 37kA, but the next standard size is 42kAIC.
 
Try as you may, you can't teach this old dog the correct terminology
(I will again try and save your answer for reference so I can look half-way intelligent)

Thanks..
That's what I was needing.... just something to say "problem" or "no"
 
augie47 said:
I don't seem to have the charts I once had but I need to have some idea of the AIC av available from a 167 kva dry type transformer 480 -240/120 volt. I know it's impedance related but I don't have that info and at one time I had some charts that showed a "common" number which is all I need a present. Anyone ?
Click to expand...

From EATON
 
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Thanks, I had one of those panic phone calls. Another inspector was en forcing 240.35 (2011) and the E/C had no idea if he might have a problem. I couldn't recall SCA (did I do good, Jim :D ) of different larger transformers to save my life. Just trying to get some idea for him.
Engineers will be involved next week... this was a "so he can sleep" call.

Thanks again. I have updated my reference files
 
augie47 said:
Thanks, I had one of those panic phone calls. Another inspector was en forcing 240.35 (2011) and the E/C had no idea if he might have a problem. I couldn't recall SCA (did I do good, Jim :D ) of different larger transformers to save my life. Just trying to get some idea for him.
Engineers will be involved next week... this was a "so he can sleep" call.

Thanks again. I have updated my reference files
Click to expand...

Augie, now you have me confused. We (TN) are not on the 2011 yet, and second, there is no 240.35 in the 2011 or 2008.:?
 
Little Bill said:
Augie, now you have me confused. We (TN) are not on the 2011 yet, and second, there is no 240.35 in the 2011 or 2008.:?
Click to expand...

My world extends beyond TN :D and, since we are not on 2011 (although some cities are within months of adopting I'm told), I used my "draft" as a guide. It looks like it may have ended up as 110.24
 
augie47 said:
Thanks, I couldn't recall SCA (did I do good, Jim :D )
Click to expand...
:thumbsup:

For a 'so I can sleep tonight' down and dirty method just multiply FLA x 50.
I cannot imagine any system that will ever have substantially more than this much SCA.
 
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