Code Change Summary: New code section requiring switchboards, switchgear, and panelboards to have a short-circuit current rating not less than the available fault current.

A short-circuit current rating is the maximum fault current at a nominal voltage to which an apparatus or system is able to be connected without sustaining damage exceeding defined acceptance criteria. Basically, the maximum amount of current that the switchboard, switchgear or panelboard can be subjected to before it reaches a level of failure outside of the acceptable criteria specified in the appropriate UL Standard.

Although this is a new code section, the concept is not. Since the 1965 NEC^®, electricians have been required by the code to consider equipment short-circuit current ratings (SCCR’s), circuit impedance, the speed at which overcurrent devices operate and other circuit characteristics in order to ensure that any installed overcurrent device can eliminate an overcurrent condition before the equipment being protected sustains extensive damage. This language is in NEC^® 110.10.

Section 110.24 requires service equipment at other than dwelling units to be legibly marked in the field with the maximum available fault current. The field marking must include the date the fault-current calculation was performed and be backed up with documentation showing how the final available fault current values were obtained.

This is only a marking requirement and does not require the electrician to do anything after the mark is applied. The intent of Section 110.24 is for the electrician to be made aware of the available fault current at the service and then install a service panelboard with appropriately rated overcurrent devices that have an interrupting rating or an ampere interrupting capacity (AIC) at least equal to the available fault current in accordance with 110.9 and 110.10.

In the 2020 NEC^®, new code language now appears in 408.6 that is somewhat of a combination of Sections 110.10 and 110.24. The new section applies to the overall short-circuit current rating of the actual switchboard, switchgear or panelboard whether used as the service, or downstream of the service. This new requirement is about the switchboard, switchgear or panelboard rather than the overcurrent devices inside them but keep in mind that some switchboards, switchgear or panelboards have a SCCR that can vary based on what type of overcurrent devices are used.

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.