This week's QOW is a continuation of the subject about electric utility data.

What data does the utility provide for arc flash studies (assuming data is provided)

(Select all that apply)

Normal conditions
Maximum fault current
Minimum fault current (line out/contingency etc.)
Infinite bus
Not sure
Depends on the utility.

I choose Depends on Utility as I have seen all the choices from utilities.

Most of the utilities that I deal with, provides maximum available fault current, although I specify to provide both Maximum & Minimum fault current in my RFI. So, I get back to them and dig the Minimum fault current and the range of their transformer impedance as well. This allows me to create multiple scenarios and analyze deeper.

Utilities are relunctan to provide this data. In the middle of the night after a storm, a line crew will replace fuses and transformers with what they have, and not with what it is supposed to be or was. One utility (name withheld) has stated they will base short-circuits on 1% transformer impedance, even though most transformers are 2% or higher. I saw a row of very old homes fed by a 350KVA transformer, The short circuit was well over the ratings of the usuall residental panelboards. Always request this data in Writing!!!