Some equipment needs to be marked with the available fault current and requires updating of that marking if modifications of the electrical system occur.

Definitions

Short Circuit Current Rating (SCCR): The prospective symmetrical fault current at a nominal voltage to which an apparatus or system is able to be connected without sustaining damage exceeding defined acceptance criteria

Interrupting Rating: The highest current at rated voltage that a device is identified to interrupt under standard test conditions.

The Code: Section 110.24

(A) Field Marking. Service equipment at other than dwelling units must be legibly marked in the field with the maximum available fault current The field marking(s) shall including 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, maintain, or operate the system

(B) Modifications. When modifications to the electrical installation affect the maximum available fault current at the service, the maximum available fault current must be recalculated 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) must be adjusted to reflect the new level of maximum available fault current.

Exception: Field markings aren’t required for industrial installations where conditions of maintenance and supervision ensure that only qualified persons service the equipment.

The purpose of this label is to allow the Short Circuit Current Rating (SCCR) of the equipment to be easily compared with the maximum available fault current. A SCCR label is usually placed on the equipment by the manufacturer.

Other Code Considerations

Section 110.9

Requires electrical equipment that is intended to interrupt current at fault levels to have an interrupting rating that is not less than the current available at the equipment’s line terminals at the circuit’s nominal voltage.

Section 110.10

Requires overcurrent-protective devices, the total impedance of the electrical circuit, electrical equipment short-circuit current ratings, and other electrical characteristics be selected to provide protection for the electrical components of the system.