NEC Chapter 2: Wiring and protection

08/14/2013


Identifying grounded conductors 

For insulated grounded conductors of 6 AWG or less, the conductor must be manufactured to meet the identification requirements. Namely, it must have a continuous white or gray outer finish or three white stripes along the entire length of the conductor. There are other options for mineral-insulated (MI) cable, photovoltaic (PV) power systems, fixture wires, and aerial cable.

  1. MI due to nature of construction requires re-identification at terminals
  2. Single-conductor, sunlight-resistant outdoor cable for PV systems allows distinctive white markings at terminations (690.31)
  3. Fixture wire allows ridges for the grounded conductor among other color options detailed in 400.22
  4. Aerial cable may be identified by a ridge on cable. 

Conductors larger than 6 AWG also require white or gray outer finish or three white stripes along the entire length of the conductor, but there is an option to re-identify the conductor by wrapping the cable with white or gray at termination points. Paint, tape, or shrink tube are good options. Just be sure the identification completely circles the conductor.

Where grounded conductors of two different systems are in the same raceway or enclosure, they must be identified differently from each other (200.6 D). Identification requirements are the same as explained above, plus there is an option to have a colored stripe other than green running along the insulation. Color code labels are required at junction boxes and at termination equipment. An example color code table:

Alternate uses for conductors

Conductors for systems greater than 50 V, identified by the manufacturer with white or gray, may be used for alternate purposes under the following conditions:

  • Conductors within a cable assembly that are not switched. Supply to the switch is allowed but return from switch is not.
  • Flexible cords as permitted in 400.22. 

Figure 4: This is a switched receptacle for a chain-hung fixture. The white conductor in NM cable has been re-identified with red tape and is connected to a hot conductor. Courtesy: CH2M HillWhere the grounded conductor is repurposed, it must be identified by encircling the conductor with a color other than white, gray, or green. Red tape is commonly used and paint is listed as an option; red shrink tube is a cleaner installation and it doesn’t fall off. The white conductor can only be used as the ”energized” leg to the switch. Troubleshooting the circuit and finding potential to ground on the white conductor clues the technician that this is a switch leg. Another advantage is that you end up with standard color coding at the device. This helps avoid confusion as to the purpose of the white conductor at the switch because it is energized under operating conditions. This practice is going to be less common because the 2011 NEC now requires that the grounded conductor also be carried to the switch and standard nonmetallic cable assemblies have only one neutral. 404.2 C is outside the scope of this article (see Figure 4). 

This receptacle is switched and common nonmetallic cable was used for a switch leg. Red tape was used to re-identify the ungrounded conductor. At the switch, while the circuit is energized, voltage can be found on the white repurposed wire.



Pete , United States, 08/21/13 12:12 PM:

Great Article, I've tried to explain same, hundreds of times, this distills it very well.
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