Medium-voltage cable tray markings

Cable trays carrying conductors operating over 600 volts must be marked with “DANGER — HIGH VOLTAGE — KEEP AWAY” at intervals not exceeding 10 feet, following NEC 392.18(H) and labeling standards.NEC Requirements

Cable trays containing medium-voltage conductors (over 600 volts) are required to have permanent, legible warning labels stating: “DANGER — HIGH VOLTAGE — KEEP AWAY”. These labels must be placed in readily visible locations along the tray, with a maximum spacing of 3 meters (10 feet) between labels to ensure continuous hazard awareness (NEC 392.18(H)), .

Label Design and Compliance

• Labels must comply with NEC 110.21(B), which requires that hazard markings effectively warn of the danger using appropriate words, colors, and symbols .
• Handwritten labels are not permitted, except for variable information such as voltage ratings or installation-specific data.
• ANSI Z535.4-2011 provides guidance on font type, size, color, capitalization, and symbol usage to ensure the label is clearly understood .

Operational vs. Rated Voltage

• The 2020 NEC clarifies that markings are required based on the operating voltage of the conductors, not just the rated voltage. For example, a conductor rated at 1000 volts but operating at 480 volts does not require a danger label unless the operating voltage exceeds 600 volts .

Exceptions

• In industrial settings where equipment is inaccessible to unqualified personnel, labels may be exempt if maintenance and supervision ensure only qualified persons service the installation .

Practical Considerations

• Ensure labels are durable and resistant to environmental conditions such as UV exposure, moisture, and chemical contact.
• Position labels at eye level or other highly visible locations along the tray, especially near entry points, junctions, and areas where personnel may work.
• Regularly inspect labels for legibility and damage, replacing them as needed to maintain compliance and safety. By following these guidelines, medium-voltage cable trays will meet NEC requirements, provide clear hazard warnings, and enhance workplace safety for personnel working near high-voltage conductors .