Code Change Summary: New code definitions and a new illustration of available fault current.

“Fault current” occurs during a short-circuit but the maximum amount of fault current that can be delivered during that short-circuit condition is the “available fault current”.

The amount of available fault current during a short-circuit depends on factors such as the length and size of the conductor supplying the faulted circuit; whether the conductors are in a ferrous metal raceway or a nonmagnetic conduit; type of conductor (copper is more noble and a better conductor of electricity than aluminum).

For many code cycles, the NEC^® has provided requirements on “available fault current” without defining what it is:

• Section 110.24 requires service equipment at other than dwelling units to be legibly marked in the field with the maximum available fault current.
• Section 240.86 provides rules on series rated overcurrent devices where the available fault current is higher than the interrupting rating of the overcurrent devices used in a series rated system.
• Section 700.4(A) requires emergency system equipment to be suitable for the maximum available fault current at its terminals.

And the list goes on.

Now, the 2020 NEC^® has brought over two new definitions of “fault current” and “available fault current” that first appeared in the 2018 NFPA 70E Standard for Electrical Safety in the Workplace.

Below is a preview of the NEC^®. See the actual NEC^® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the 2020 NEC^® edition of NFPA 70.