110.24 Available Fault Current.
(A) Field Marking. Service equipment at other than dwelling
units shall be legibly marked in the field with the maximum
available fault current. The field marking(s) shall include the
date the fault-current calculation was performed and be of
sufficient durability to withstand the environment involved.
The calculation shall be documented and made available to
those authorized to design, install, inspect, maintain, or operate
the system.
Informational Note: The available fault-current marking(s)
addressed in 110.24 is related to required short-circuit current
ratings of equipment. NFPA 70E -2015, Standard for Electrical
Safety in the Workplace, provides assistance in determining the
severity of potential exposure, planning safe work practices, and
selecting personal protective equipment.
(B) Modifications. When modifications to the electrical installation
occur that affect the maximum available fault current at
the service, the maximum available fault current shall be verified
or recalculated as necessary to ensure the service equipment
ratings are sufficient for the maximum available fault
current at the line terminals of the equipment. The required
field marking(s) in 110.24(A) shall be adjusted to reflect the
new level of maximum available fault current.
Exception: The field marking requirements in 110.24(A) and
110.24(B) shall not be required in industrial installations where conditions
of maintenance and supervision ensure that only qualified
persons service the equipment.
