Yes, there are absolutely code requirements to label junction boxes with multiple power sources. Here's a breakdown: NEC 110.21(B) Marking Requirements. Legibility and durability

This section emphasizes that labels must be durable enough to withstand the environment and clearly legible. They shouldn't fade, peel, or become unreadable easily.

NEC 110.21(B)(1)

The marking must contain the manufacturer's name or trademark symbol and the rated voltage.

NEC 408.4(A) Marking Requirements

In the instance of having more than one source feeding the box. Each source should be labelled. This section requires the original manufacturer marking not to be removed.

NEC 701.10(B)(5) Identification of Power Sources

For emergency systems, it requires the source of power to be identified.

OSHA Regulations

While the NEC is a consensus standard and not law unless adopted by a local jurisdiction, OSHA incorporates many NEC requirements by reference. Failure to comply with NEC labeling requirements could be a violation of OSHA regulations regarding electrical safety.

Best Practices and Considerations



Clear and Concise Language

Use language that anyone (including future technicians) can easily understand. Avoid jargon or overly technical terms.

Permanent Labeling Methods

Consider engraved plastic labels, durable printed labels with a protective over laminate, or even directly etching or stamping the information onto the box (if the box material allows).

Placement

Place the labels prominently and near the point where the conductors enter the junction box.*

Color Coding (Optional but Recommended)

Consider using color-coded labels to further differentiate the sources (e.g., red for Source 1, blue for Source 2). While not explicitly required, it adds another layer of safety and clarity.

In summary, YES, you absolutely MUST label the junction box with the identification of each power source, its voltage, and relevant characteristics. Failure to do so is a safety hazard and a code violation. It's well worth the time and effort to do it right. Consult with a licensed electrical contractor or inspector if you have any doubts about the specific requirements for your installation. Flag for review