Wednesday, February 22, 2023
Hi CQD, we are finishing up the wiring of a new 3 story office building. The inspector is asking for a short circuit study. We have never been required to provide this before. Why are they asking for this? Is it required by the code? Regards, Thomas Vollrath
Hi Thomas, A “Short Circuit Current Study” of “Fault Current Study” is a point to point one-line diagram that shows the maximum available fault current at each point throughout the electrical distribution system. It starts with the maximum available fault current value at the service connection point, which is established by the utility. This value can be obtained from the utility and provided to an engineer or other qualified person to calculate the available fault current at each point on the electrical system. There is a misnomer out there that fault current is addressed at the service only, and everything else downstream is protected by the service OCPD. This is not true, as there is level of available fault current that extends beyond the service, downstream to all points on the electrical system.
A “Short Circuit Current Study” is indirectly required by the NEC® as follows:
- NEC 110.9 & 110.10 requires that all electrical equipment and OCPDs must be rated for the for the available fault current present.
- There are several Code Sections requiring the available fault current and the date the calculation was performed, to be posted on the electrical equipment.