Figuring AIC of panels/breakers.....

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chevyx92

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VA BCH, VA
If I know that I need a 22KAIC rating on my 3P 480V Main Breaker how do I know my KAIC ratings down stream after the step down transformer? I know the main rating because POCO gave me the fault current information. I know secondary estimated load is about 300A @ 208V.
 
You will need to perform an available fault current calculation for the system.

Go HERE and click on the fault current calculator and it will allow you to download a free Excel spreadsheet with the point to point method.

Chris
 
raider1 said:
You will need to perform an available fault current calculation for the system.

Go HERE and click on the fault current calculator and it will allow you to download a free Excel spreadsheet with the point to point method.

Chris
Click to expand...
If that is same calculator I have downloaded before (I did not open your link, but appears to be the one on Mike Holt's site, which I have downloaded before) it will not accurately give you load side results of a separately derived system. You can start from the top at the separately derived system - but it is going to assume infinite capacity from the transformer input, which will leave you with a higher then actual result. Many times that works, but when you get to the point where you are on borderline of one kA rating or another from your equipment it can be a costly decision made if you choose not to have more accuracy.
 
We are trying to figure out the KAIC rating for our equipment, We have the sheets from the utility yet we are not able to make sense of this, Could anyone help out please? Here are the values listed below.

400A Main
120/240 1Phase 3 wire
(Gen Only)
ESG=50kw
VD=2.47V
VR=1.42V
VF=0.73V
SCI=25000A

Thank you,
 
You can not determine the AIC of breaker, that must be done by the manufacturer. You can chose or specify an AIC value that exceeds your available Short Circuit Amps (SCA).

Based on the data you provide I would assume the utility value for SCI is what I called SCA, therefore you need a panel and breakers rated for 25kA.
 
kwired said:
If that is same calculator I have downloaded before (I did not open your link, but appears to be the one on Mike Holt's site, which I have downloaded before) it will not accurately give you load side results of a separately derived system. You can start from the top at the separately derived system - but it is going to assume infinite capacity from the transformer input, which will leave you with a higher then actual result. Many times that works, but when you get to the point where you are on borderline of one kA rating or another from your equipment it can be a costly decision made if you choose not to have more accuracy.
Click to expand...
It lets you add a transformer to a system, so you start with utility current, put in the service conductors and then add a transformer to that system. That will use the calculated fault current at the end of the service conductors as the primary current for the transformer.
 
don_resqcapt19 said:
It lets you add a transformer to a system, so you start with utility current, put in the service conductors and then add a transformer to that system. That will use the calculated fault current at the end of the service conductors as the primary current for the transformer.
Click to expand...
I will share this with my partners and appreciate the fast feedback.
 
There is not enough information provided for someone to perform their own fault current calculations. The utility does not specify which point in the system where their values are located. A number as specific as 25,000 tells me that it is a made up or default value.

In this area utilities provide the SCA that they want your equipment sized for, especially on a small service like this.
 
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