Code Change Summary: The marking requirements for signs in 600.4 were reduced and clarified to remove duplication with existing product standards.

SME commentary: In the 2026 NEC^®, Section 600.4 was revised to streamline sign marking requirements by deleting former subsections 600.4(A), (C), and (E), and consolidating the remaining provisions under a simplified structure. Revised Sections 600.4(A) and (B) are all that remain. The revisions were prompted by public input noting overlap between NEC^® marking requirements and those already mandated by product standards UL 48, Standard for Electric Signs, and UL 879A, Standard for LED Sign Retrofit Kits. Section 600.2 already requires signs and retrofit kits to be listed, labeled, and installed in accordance with the product listing, which includes the manufacturer’s required markings and installation instructions. Removing the redundant code language in 600.4 improves clarity and reinforces the NEC’s focus on installation requirements rather than manufacturer obligations already governed by product safety standards.

Under UL 48, Section 7.2.1, all listed signs and outline lighting systems are already required to bear the manufacturer’s identity, voltage, and current markings. Likewise, UL 879A, Section 26, requires sign retrofit kits to include appropriate instructions. Because these details are already incorporated into the product listing, maintaining parallel requirements in the NEC^® introduced unnecessary repetition and complexity without improving safety.

The deletion of 600.4(E) eliminates the prior mandate that all signs and retrofit kits be marked to indicate that installation instructions are “required.” This language, first added in 2014, was determined by the Code-Making Panel to be redundant and potentially confusing, as product standards already require manufacturers to provide these instructions. The change removes an unneeded phrase that had no direct enforcement value.

Remaining provisions in 600.4(A) retain essential marking requirements for signs with retrofitted illumination systems, ensuring that it is evident the illumination system has been replaced and that markings identify the kit provider and installer’s name, logo, or unique identifier.

For signs equipped with tubular LED lamps powered by the existing sign sockets, the code still requires a label alerting service personnel that the sign has been modified. The label must be visible during relamping, meet the requirements of 110.21(B), and also include a warning not to install fluorescent lamps.

These markings preserve field safety and inspection clarity for retrofitted signs, where the potential for component substitution remains a valid concern.

Revised 600.4(B) reorganizes the visibility requirement for listing labels and voltage markings, clarifying that such labels must remain permanently affixed and visible prior to servicing, but may be installed where they are not visible to the public. This reinforces practical field application while aligning the NEC^® text with current product marking and labeling conventions.

This alignment of Section 600.4 with UL standards and removal of redundant requirements intends to improve usability for installers and inspectors. The revision maintains critical safety labeling for modified or retrofitted signs while eliminating unnecessary or duplicative language that offered no additional protection.

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 2026 NEC^® edition of NFPA 70.

2023 Code Language:

600.4 Markings.

(A) Signs and Outline Lighting Systems. Signs and outline lighting systems shall be listed and labeled; marked with the manufacturer’s name, trademark, or other means of identification; and input voltage and current rating.

(B) Signs with a Retrofitted Illumination System. Signs with a retrofitted illumination system shall contain the following:

(1) The sign shall be marked that the illumination system has been replaced.

(2) The marking shall include the kit providers and installer’s name, logo, or unique identifier.

(3) Signs equipped with tubular light-emitting diode lamps powered by the existing sign sockets shall include a label alerting the service personnel that the sign has been modified. The label shall meet the requirements of 110.21(B). The label shall also include a warning not to install fluorescent lamps and shall also be visible during relamping.

(C) Signs with Lampholders for Incandescent Lamps. Signs and outline lighting systems with lampholders for incandescent lamps shall be marked to indicate the maximum allowable lamp wattage per lampholder. The markings shall be permanently installed, in letters at least 1⁄4 inch high, and shall be located where visible during relamping.

(D) Visibility. The markings required in 600.4(A) and listing labels shall be visible after installation and shall be permanently applied in a location visible prior to servicing. The marking shall be permitted to be installed in a location not viewed by the public.

(E) Installation Instructions. All signs, outline lighting, skeleton tubing systems, and retrofit kits shall be marked to indicate that field wiring and installation instructions are required.

2026 Code Language:

600.4 Markings.

(A) Signs with a Retrofitted Illumination System. Signs with a retrofitted illumination system shall contain the following:

(1) The sign shall be marked that the illumination system has been replaced.

(2) The marking shall include the kit providers and installer’s name, logo, or unique identifier.

(3) Signs equipped with tubular light-emitting diode lamps powered by the existing sign sockets shall include a label alerting the service personnel that the sign has been modified. The label shall meet the requirements of 110.21(B). The label shall also include a warning not to install fluorescent lamps and shall also be visible during relamping.

(B) Visibility. Listing labels and markings that identify the input voltage and current rating shall be visible after installation and be permanently applied in a location visible prior to servicing. The marking shall be permitted in a location not viewed by the public.