High-voltage cable tray markings

Cable trays carrying conductors over 600 volts must be marked “DANGER — HIGH VOLTAGE — KEEP AWAY” at intervals not exceeding 10 feet, with labels complying with NEC 110. 21(B) and ANSI Z535. 4 standards.

NEC Requirements

According to NEC 392. 18(H), any cable tray containing conductors rated over 600 volts must be marked with a DANGER label stating: “DANGER — HIGH VOLTAGE — KEEP AWAY” at intervals no greater than 10 feet along the tray. These labels must be permanent, professionally printed, and cannot be handwritten except for variable information.

The labeling must effectively warn of the hazard using appropriate words, colors, and symbols as specified in NEC 110. 21(B).

Label Design Standards

The NE

C references ANSI Z535. 4-2011, which provides detailed guidance on hazard sign design, including: Font type and size for readabilityColor coding (typically red for danger)Use of symbols to indicate electrical hazardsCapitalization and text hierarchy to ensure the hazard is immediately clearPlacement of supporting information on the label These standards ensure that the warning is visible, legible, and understandable to anyone near the cable tray.

Exceptions

An exception exists for inaccessible equipment in industrial establishments where maintenance and supervision ensure that only qualified personnel service the installation. In such cases, marking may not be required.

Practical Considerations

Labels should be durable and resistant to environmental conditions such as moisture, heat, and UV exposure. Placement should not obstruct access or interfere with cable tray function. Regular inspection is recommended to ensure labels remain legible over time.

Compliance with UL marking guides can provide additional assurance that the installation meets safety and code requirements. By following these requirements, high voltage cable trays will meet NEC compliance, provide clear hazard warnings, and enhance safety for personnel working near or around electrical installations.