Section 14/Ground Potential Rise
IEEE 80 Section 14 establishes tolerable step and touch voltage limits based on body weight, surface material, and fault duration.
The ground potential rise (GPR) is the maximum voltage the grounding grid reaches during a ground fault, calculated as the product of the fault current flowing through the grid and the grid resistance to remote earth. GPR = Ig x Rg, where Ig is the grid current (total fault current minus the portion returning through overhead ground wires and neutral paths) and Rg is the grounding system resistance. The GPR determines the voltage exposure at the substation fence and at communication circuits entering the substation. When GPR exceeds safe limits, special measures are required for personnel protection and equipment isolation.
Why this section exists
During a ground fault at a substation, the entire grounding grid rises in voltage relative to remote earth. This voltage appears at the fence, equipment pads, and any metallic paths leaving the station (communication cables, water pipes, railroad tracks). A person standing outside the fence touching a grounded conductor experiences the full GPR as a touch voltage. Communication equipment connected between the substation and a remote location sees the GPR as a voltage surge. The GPR calculation determines whether the grounding design provides adequate protection.
What plan reviewers look for
Plan reviewers check the grounding study for the GPR calculation including the assumed fault current, current split factor, and grid resistance. They verify the fault current comes from the short- circuit study. They check the current split (how much returns through ground wires vs. through the grid). They verify the grid resistance from the soil resistivity analysis and grid geometry.