While teaching codes and standards across the United States, the question often arises why the National Electrical Code (NEC) incorporates so many requirements for signage. For example, orange has historically served as a warning to electrical personnel. The orange high-leg in a delta system usually signifies that the voltage is 208 volts (V) to ground. Until the 1975 NEC, orange on a 480Y/277V (wye) system identified the center phase as 277V to ground and not 120V to ground as in a 208Y/120V (wye) system. Orange wiring in industrial machines signifies that the wiring remains energized if the main supply has been disconnected. Other sections in the NEC also require signage.
Arc flash hazard warning
Section 110.16 of the NEC warns of the arc flash hazard, and Section 130.5(C) of NFPA 70E warns of other items to be placed on the equipment label.
Available fault current
Unless the Exception to Section 110.24(A) and (B) is applied, service equipment (other than dwelling units) is required to have the available fault current field marked on the service equipment enclosure and when modifications are made that change the current value.
The method of identifying the grounded conductor from another system requires signage that properly identifies the grounded conductor from each system.
Identifying ungrounded conductors
When an electrician forgets the sections that cover procedures for identifying the ungrounded conductors as required in NEC Section 210.5(C)(1) through (C)(3), refer to Section 310.110(C), which sends the Code user to 210.5(C) for branch circuits and 215.12(C) for feeder identification of the ungrounded conductors. Note that the method used must be posted.
Identifying disconnecting means
Where a building or structure is equipped with any combination of branch circuits, feeders or services passing through or supplying it, a permanent plaque or directory shall be installed to denote the location of each in a manner that easily identifies where one is located from the other.
A permanent, legible, warning notice worded “Danger-High Voltage” must be placed in a conspicuous place at all entrances and access points to substations with a requirement not to exceed 10 feet in all cable trays where high-voltage cables are present. Additionally, a permanent, legible sign also must be placed at each isolation switch. Designers and installers should consult Section 110.34(C), which requires “Danger-High Voltage-Keep Out” to be placed in such installations. Per Section 225.70(A)(3), a suitable warning sign must be erected to alert operators not to replace fuses while the circuit is energized. To warn personnel of a voltage backfeed problem, a similar notice must be provided as Section 225.70(A)(4) outlines.
Metal-enclosed, metal-clad switchgear
Unless Exception (a) to Section 225.70(A)(5) is applied, a permanent, legible, single--line diagram of the switchgear must be provided in a readily visible location within sight (defined in Article 100) of such switchgear, and this diagram must identify interlocks, isolation means that include all voltages that might pertain to the normal or emergency operation of the installation. Section 225.70(A)(5)(b) requires panels or doors that provide access to high-voltage energized conductors or parts to carry a notice with the wording “Danger-High Voltage.” Again, see Section 110.34(C). Where the utility is involved, refer to Section 225.70(A)(5)(c), which requires a notice for limitation for utility use only.
Service-entrance conductor sets
Where the number of service disconnecting locations exceeds six for any given supply classification, they shall be clearly described with graphics, text or both on plaques that are located in readily accessible and visible areas.
Service-entrance conductors in cable trays
Cable trays containing service-entrance conductors in accordance with Section 230.44 must be provided with permanent affixed labels with the wording “Service-Entrance Conductors.” Such labels must be visible at 10-foot intervals, so they are readily traceable throughout the length of the cable tray. Section 392.18(H) provides further verification of this requirement.
Systems that operate ungrounded must be legibly marked “Ungrounded Systems” at the source or first disconnecting means of the system. This requirement per 250.21(C) notifies electrical personnel that the electrical system is operating ungrounded.
This article does not cover all the labels, plaques, directories and markings that the 2011 NEC requires. It does not even cover all the existing requirements of the 2008 NEC. Designers, installers and inspectors have the responsibility to cover signage requirements outlined in the NEC and other standards.
STALLCUP is the CEO of Grayboy Inc., which develops and authors publications for the electrical industry and specializes in classroom training on the National Electrical Code and other standards, including those from OSHA. Contact him at 817.581.2206.