Section 110.24/Available Fault Current Documentation
NEC 110.24 requires the available fault current to be documented at service equipment. Here is what the section requires, how plan reviewers check for compliance, and the most common violations on electrical drawings.
The available fault current must be field-marked on service equipment. The marking must be visible and include the date the calculation was performed and be of sufficient durability to withstand the environment. When modifications to the electrical installation affect the maximum available fault current, the marking must be verified or recalculated to ensure the equipment rating is still adequate.
Why this section exists
Electrical equipment has a maximum fault current rating, often called the AIC (ampere interrupting capacity) or SCCR (short circuit current rating). If the available fault current at the service entrance exceeds the equipment's rating, a short circuit event can cause equipment to fail catastrophically rather than interrupting the fault safely. This section ensures that the available fault current is documented so that equipment ratings can be verified against actual site conditions.
Before this requirement was added to the NEC, it was common for electrical equipment to be installed without anyone verifying that the available fault current was within the equipment's rating. The utility transformer size, the service entrance length, and the conductor sizing all affect the available fault current. When the utility upgrades a transformer on the street, the available fault current at the building can increase, potentially exceeding the original equipment rating.
What plan reviewers look for
Plan reviewers checking compliance with this section look for three things on the electrical drawings: the available fault current value stated on the one-line diagram or in the panel schedules, the AIC or SCCR rating of the service entrance equipment shown to be equal to or greater than the available fault current, and a note indicating the date of the calculation or referencing the utility's fault current data.
If the utility has not yet provided the fault current information at the time of permit submittal (which is common for new construction where the utility service is not yet designed), the reviewer typically accepts a note on the drawings committing to verify the available fault current and equipment ratings before energization. However, some jurisdictions require the actual value at the time of permit.
Common violations
Related NEC requirements
Section 110.9 covers the general requirement that all equipment intended to interrupt current at fault levels must have a sufficient interrupting rating. Section 110.10 addresses the requirement that overcurrent protective devices, equipment, and conductors must be selected and coordinated to withstand the fault current without extensive damage. Together with 110.24, these three sections form the fault current compliance framework in the NEC.
For arc flash analysis, Section 110.16 requires warning labels on equipment likely to be serviced while energized. The available fault current documented under 110.24 is one of the inputs to the arc flash hazard calculation per IEEE 1584.