Section 110.24/Available Fault Current Documentation (2020 Edition)
NEC 2020 Section 110.24 requires fault current documentation at the service, narrower scope than the 2023 expansion.
The available fault current must be field-marked on service equipment, along with the date the calculation was performed. The marking must be of sufficient durability to withstand the environment. When modifications to the electrical installation affect the maximum available fault current, the documentation must be updated. The 2020 edition maintained the 2017 requirement and clarified that the fault current must be recalculated when upstream utility changes affect the available fault current at the service.
Key differences from NEC 2023
The 2023 NEC expanded 110.24 to require fault current documentation at additional locations beyond the service equipment, including at industrial control panels and motor control centers. The 2020 edition requires marking only at the service equipment. Jurisdictions on the 2020 NEC have the narrower requirement.
What plan reviewers look for
Plan reviewers check the one-line diagram for the available fault current value at the service entrance. They verify that the calculation accounts for the utility transformer size and impedance, the service conductor length, and the total impedance to the service equipment. They check that the interrupting rating of the service disconnect exceeds the available fault current.