Available Fault Current Calculation

[SPierce]

Good morning all! I've used Mike Holt's Fault Current calculator several times and it works well for most applications. But there doesn't seem to be an option for overhead services with open-air conductors. Also, it asks for the size of wire and whether you're using aluminum or copper. Well, the size and type of wire used in the service mast is different than the wire that the POCO uses. Does that become a factor? Is there a calculator on-line that's available? Any help is appreciated. Thanks!

 

[Carultch]

Good morning all! I've used Mike Holt's Fault Current calculator several times and it works well for most applications. But there doesn't seem to be an option for overhead services with open-air conductors. Also, it asks for the size of wire and whether you're using aluminum or copper. Well, the size and type of wire used in the service mast is different than the wire that the POCO uses. Does that become a factor? Is there a calculator on-line that's available? Any help is appreciated. Thanks!

I recommend setting it to conductors in PVC, to approximate the same physics as you'll get for open air conductors. The intent of that dropdown is to determine if the steel raceway affects the magnetism of region surrounding the conductors, which adds inductive impedance that affects fault current (usually reduces it). In the case of PVC or open air conductors, a ferrous raceway is not present and will not add this effect.

 

[don_resqcapt19]

Bussmann has a nice app for your smart phone...http://www.cooperindustries.com/content/public/en/bussmann/electrical/resources/fc2.html

 

[SPierce]

Thanks Don! I've looked at the Bussman app and downloaded it - I like how it operates. I still wonder if the calculation should be based solely on the size and type of wire the POCO installs? Or does it play into the calculation at all if the POCO installs an aluminum, open-air cable and the contractor installs copper conductors in a metal conduit?

 

[Carultch]

Thanks Don! I've looked at the Bussman app and downloaded it - I like how it operates. I still wonder if the calculation should be based solely on the size and type of wire the POCO installs? Or does it play into the calculation at all if the POCO installs an aluminum, open-air cable and the contractor installs copper conductors in a metal conduit?

If you have dissimilar circuit construction along the length of the same circuit, then the way to calculate it is to first calculate the fault current from the transformer to the splice point, and then use that as the fault current input for the length of conductor from the splice point to the service equipment.


You need to do some creative work-arounds with these calculation spreadsheets, while keeping in mind that it is a point-to-point method. In the spreadsheet that you download from MH's website, every section is a different point-to-point stage.