Code Change Summary: Previous requirements in 110.16(B) were shortened up but also expanded to include equipment supplied by a feeder.

In the 2020 NEC^®, this section required service equipment in other than dwelling units to be marked with several items unless an arc flash label was applied in accordance with “acceptable industry practice”. The item that most electrician struggled with was marking the clearing time of service overcurrent devices based on the available fault current at the service equipment.

Most electricians (with the help of the electric utility company) can determine and mark the available fault current at the service which has been required by Section 110.24 for several code cycles.

Determining the clearing time of the overcurrent device based on the available fault current is a duty typically handled by the electrical engineer responsible for the project (if there is one).

Determining and marking the clearing time of an overcurrent device requires an understanding of time-current curve charts for the overcurrent device. Even if the electrician understands how to read the time-current curve charts for the service overcurrent devices, the electrical inspector might not. An electrical inspector may want proof that the marking of the clearing time (placed by the electrician) required by Section 110.16(B) depicts an accurate value. Does the electrical inspector know how to verify that the electrician marked an accurate clearing time at the service equipment?

In addition, the available fault current is never the same from job to job and changes based on field conditions. If the utility transformer ends up being larger or having less impedance than originally shown on the plans, then the available fault current at the service will be higher than originally specified. If the service conductors between the secondary side of the utility transformer and the service equipment are shorter or larger than originally specified, then the available fault current will be higher than originally specified. Variances in the amount of available fault current have an impact on the actual clearing time of an overcurrent device.

The NEC^® previously required a “field or factory” marking of the clearing time. The factory might not have access to know the available fault current that will be present at the electrical service in order to provide a “factory marking” of the clearing time for the specific job site conditions.

In the 2023 NEC^®, “Feeder supplied equipment” was added to the title and the requirements of Section 110.16(B). Now, this section applies to service equipment and feeder supplied equipment, but the rules only pertain to equipment in other than dwelling units.

The language was further revised to apply to equipment rated 1000 amps or more instead of 1200 amps or more to increase worker safety.

The previous list items (1)-(4) and the exception were removed and incorporated into the text of 110.16(B) in sentence and paragraph format, rather than a list format.

The concept of marking “the clearing time of service overcurrent protective devices based on the available fault current at the service equipment” was removed and replaced with a requirement for the arc flash label to be “in accordance with acceptable industry practice and include the date the label was applied”.

Not every job or project will involve an electrical engineer. Some service change or panelboard installation permits for commercial and industrial occupancies can be pulled by the electrician without electrical engineer involvement. For installations including service equipment or feeder supplied equipment rated 1000 amps or more, be prepared to create an arc flash label in accordance with “applicable industry practice”.

“Acceptable industry practice” for this type of marking requirement will typically be something in accordance with the language in NFPA 70E, the 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 2023 NEC^® edition of NFPA 70.