Available fault current

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Jpflex

Jpflex

Electrician big leagues
Location
Victorville
Occupation
Electrician commercial and residential
Is the formula for available fault current for a transformer KVA divided by secondary voltage for single phase or voltage x 1.732 for 3 phase

Then the resultant secondary I amperes is divided by the transformers impedance percentage?

But if this is correct how do you compute primary utility conductors resistance/ figures and therefore small reduction to maximum available fault current for NEC required labeling?
 
Primary utility conductors data is not needed. Just ask your Poco for a chart of transformer available short circuit current at secondary terminals
 
I had a utility engineer in Jacksonville say they just use infinite buss in their calculations, so if you know the transformer size and impedance, then you can do your own calculations.
 
tom baker said:
Primary utility conductors data is not needed. Just ask your Poco for a chart of transformer available short circuit current at secondary terminals
Click to expand...

I think I can find short circuit current at secondary but I read somewhere online that you must measure distance from first transformer to final transformer and include these figures or maybe it was secondary wire distance?
 
hillbilly1 said:
I had a utility engineer in Jacksonville say they just use infinite buss in their calculations, so if you know the transformer size and impedance, then you can do your own calculations.
Click to expand...

So this goes back to what I said about using transformer secondary current calculation divided by transformer nameplate impedance? Was my first post calculation therefore correct?
 
hillbilly1 said:
Eaton has a nice free app to do the calculations for you.
Click to expand...

But Instead of asking utility what if I want to know this formula for my own, especially if trying to take my journeyman’s license test later?
 
hillbilly1 said:
Good point, but since I already have all the licenses I need (journeyman and masters) I like quick and easy! LOL!
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Yes my old boss said the same thing. He doesn’t do dwelling load calculations any more but used software to do it for him. He says that what I’m doing is old school.

By the way how much more areas are you required to master, for masters electrician license vs basic journeyman license.

I plan to go all the way, journeyman to electrical engineer to master
 
Jpflex said:
Yes my old boss said the same thing. He doesn’t do dwelling load calculations any more but used software to do it for him. He says that what I’m doing is old school.

By the way how much more areas are you required to master, for masters electrician license vs basic journeyman license.

I plan to go all the way, journeyman to electrical engineer to master
Click to expand...
Varies greatly state to state. A lot of states require business regulations knowledge for the masters, which is not required on the journeyman. In Georgia, they don’t have a journeyman license, they just have two classes, class I, and class II, class II is the masters, and class I is basically a residential license. In Indiana, the licenses are through the cities. Michigan and Florida has journeyman licensing.
 
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