Fault current question

[BJAP]

OK. I have looked at the utility's fax. It has blank spots that are filled in by hand. One of these is "ultimate" fault current.

I am not certain exactly what is represented by the phrase, ?ultimate 171,800 amps symmetrical at 240 volts.? But it certainly has nothing to do with the fault current available at a specific user?s transformer location. As evidence, I offer the fact that a city in Houston (served by the same utility company as the OP is discussing) has published a list of requirements related to permits and construction. Here it is (copy into browser to view the document):
[FONT='Arial','sans-serif']www.bunkerhill.net/Government/Permits/Contractor%20Permit%20Package%20122007.pdf[/FONT]

On page 18 of that document, it declares that the local utility?s value of ultimate fault current, for single or three phase, is 171,800. So clearly that number is not related to any given installation.

The number you should be using as the basis for the rating of any equipment within your building need be no higher than the 12,300 amps that the utility shows as ?initial fault current.?

Charlie,

The formula sheet that was given to me and the one I faxed you some how forms a number the inspector is looking for. Is the 12,300 number you gave as the initial fault current based on the formula sheet? thanks

 

[charlie b]

Is the 12,300 number you gave as the initial fault current based on the formula sheet? thanks

I didn't do any math, so I don't know how they arrived at the value of 12,300. All I can say with confidence is that the value of 171,800 amps has nothing to do with any specific installation, and your equipment need not be rated for that level of fault.

Your application form has a name (Fernando F.) and phone number for a utility contact. I suggest calling him, and getting him to explain the two numbers they gave you for fault current (initial and ultimate).

 

[BJAP]

It looks like I may have misunderstand what the inspector wanted. The formula sheet says short circuit calculation. Is the short circulation available with the info from above? It says Line to Line and Line to Neutral. thanks

 

[BJAP]

Figured it out ! thanks for all who gave input.

 

[nakulak]

and what was the result you figured out ?

 

[alfer_cbk@yahoo.com.ph]

What are the wire size for three 100kva single phase to 3 phase transformer

What are the wire size for three 100kva single phase to 3 phase transformer

Please give me an idea to what size of wire to to use in connecting three 100kva transformer to be connected to form three phase.