On any given project, choosing the appropriate colors for conductors during installation facilitates maintenance and enhances troubleshooting efforts later on. The universal language of colors clarifies the intent of the original installation, thereby enhancing safety and efficiency for those who will work on the electrical system for years to come. Although most color coding is mandated by the National Electrical Code (NEC), there are some trade practices that make good sense, even if they're not required. Adhering to these additional guidelines and making them part of your work protocol will inevitably lead to more professional installations.

The NEC gives explicit directives on color coding, but not in any one article or chapter. In fact, there are more than 20 major NEC locations that address color coding. NEC 2008 does not contain big changes in this area. The last major change was in NEC 2005 with the addition of Art. 210.5, which required enhanced identification where different voltage or phase systems are in the same building.

Most fundamental from the point of view of safety and functionality is the distinction between grounded and ungrounded conductors. Grounding conductors (which are ideally at the same potential as grounded conductors but serve a different purpose) are color coded differently so that they can be connected properly (Photo 1 on page C20).

Grounded conductors

Permitted methods of identification for grounded conductors depend upon size. For 6 AWG and smaller, an insulated grounded conductor must be white or gray — or have three continuous white stripes in other than green insulation along its entire length. At one time, the Code talked about “natural” gray insulation. However, that word was dropped as meaningless, because it would imply that there was such a thing as “unnatural” gray, which could not be used. A Fine Print Note (FPN) points out that gray may have been used in the past for ungrounded conductors, so care must be used when working on older systems.

It is not permitted to re-identify an ungrounded conductor as grounded in the field for sizes 6 AWG and smaller (Photo 2) except in certain cases, which are:

  • Mineral-insulated, metal-sheathed cable (Type MI)

  • Single-conductor photovoltaic outdoor-rated sunlight-resistant cable

  • Fixture wire

Aerial cable is permitted to have a ridge along its entire length instead of white, gray, or three white stripes.

Also noteworthy is that colored tracer threads to show the source of manufacture are permitted and do not nullify the color coding requirements of the Code.

For sizes larger than 6 AWG, a different set of NEC rules applies (Photo 3), because it would be impractical to stock these sizes in various colors. There would also be more waste, generating many cutoffs instead of just one for the whole job. Besides the white, gray, or three white stripes along the entire length as allowed for smaller conductors, conductors larger than 6 AWG may have white or gray marking at all terminal points. This can be paint or tape completely encircling the conductor. For grounded conductors larger than 6 AWG that simply pass through an enclosure without termination, such as those within a pull box, re-identification is not required.

Returning to all size conductors, an insulated grounded conductor in a flexible cord may be identified by a white or gray outer finish or white or gray braid, a white or gray tracer in the braid, or a white or gray separator. For cords having insulation integral with the jacket, individual tinned strands may identify the grounded conductor. In addition, ridges, grooves, or white stripes on the exterior of the cord may signify the grounded conductor.

Where different systems are present within the same raceway, cable, or enclosure, the grounded conductor of each must have a different means of identification, all of which have to conform to the rules outlined above. The means of identification must be posted at each branch-circuit panelboard. Although not Code mandated, trade practice is to use white for the lower voltage and gray for the higher voltage grounded conductor (Photo 4). Where multiple systems are present within the same raceway, cable, or enclosure, differing colored stripes other than green along the entire length of white insulation will suffice.

Where conditions of maintenance and supervision ensure that only qualified persons service the installation, grounded conductors in multiconductor cable may be identified at terminations by white paint or tape that completely encircles the conductor. This exception applies to all sizes.

In addition to the foregoing means of identification, the Code also stipulates that white or gray conductors, other than green with three continuous white stripes and conductors marked white or gray at terminations, may not be used for anything but grounded conductors except for the following limited cases:

  • Circuits of less than 50V, unless required to be grounded. (This is an exception within an exception.) Examples are thermostat control circuits and telephone lines.

  • Circuits of 50V or more, where re-identified. Notice that in the case of conductors 6 AWG or smaller, white may be re-identified black, but black may not be re-identified white. Larger black conductors may be re-identified white.

  • For switch loops, white conductors may be used as grounded conductors, but they must be re-identified. Prior to the 1999 NEC, a white ungrounded conductor supplying a switch did not have to be re-identified because its use was considered self-evident. However, now both supply and return conductors must be re-identified.

The Code also stipulates color coding for terminals. Unless it is clearly evident which terminal is to be grounded — as in the case of panelboards — the grounded terminal must be white or of silver finish, or be marked with the word “White” or the letter “W.”

Grounding conductors

For equipment-grounding conductors, the color coding is somewhat different. The equipment-grounding conductor, unless separately derived, originates in the service equipment where it is connected to the neutral by means of the main bonding jumper. From there, it accompanies the other conductors to every outlet, never to rejoin the grounded conductor. Even an ungrounded system must have an equipment-grounding conductor.

Grounding conductors may be bare, covered, or insulated. If they are insulated, they must be green or green with one or more yellow stripes. They may not be re-identified for use as grounded or ungrounded conductors.

Like grounded conductors, grounding conductors larger than 6 AWG may be re-identified. Permitted methods are stripping the insulation or covering from the entire exposed length, coloring the exposed insulation green, or marking the exposed length with green tape or adhesive labels. Any means of re-identification must entirely encircle the conductor. Such re-identification is not required in conduit bodies that contain no splices or unused hubs.

In flexible cord, a bare equipment-grounding conductor is allowed. However, if it's individually covered, the covering has to be green or green with one or more yellow stripes.

Ungrounded conductors

Despite the innocuous sounding name, ungrounded conductors are more hazardous than the conductors covered so far. Colloquially, an ungrounded conductor is called the “hot wire” and with good reason. Because it is at a different voltage potential from ground — and people are almost always at least partially grounded — contact with one of these conductors can cause injury or death. Therefore, it is critical for these conductors to be correctly and consistently color coded. A fundamental NEC requirement is that ungrounded conductors be finished to be clearly distinguishable from grounded and grounding conductors, and that these markings shall not obscure the size and other required markings. Further details are provided separately for branch-circuit ungrounded conductors and?ungrounded feeders.

Like grounded conductors, ungrounded conductors have to be separately identified when different systems are involved, but there is an important distinction. Grounded conductors must be differentiated by system only when they are present in the same raceway, cable, or enclosure but accessible ungrounded conductors of different systems must be differentiated whenever they appear in the same building. The means of identification is up to the electrician. It may be by color coding, marking, or tagging. It has to be consistent and is to be permanently displayed at each panelboard or distribution equipment.

The usual means of identification is color coding. Phase tape (regular electrical tape), which is available in many colors, is easier to use, and is more durable than paint. The means of identification must completely encircle the conductor. The Code does not specify which colors to use except not white, gray, or green. However, for years industry practice has been to use brown, orange, and yellow for the higher voltage (typically 480Y/277V) and black, red, and blue for the lower voltage (208Y/120V).

Specialized color coding

So far, we've looked at the rules for grounded, grounding, and ungrounded conductors, but there are other situations you may encounter in the field. Here are some of those special applications.

If the midpoint of a 4-wire, 3-phase delta-connected system is grounded, the high-voltage phase conductor or bus bar (usually called the B phase) must be orange, or other effective identification may be used. This identification is to appear wherever a connection is made if the grounded conductor is also present.

The non-heating leads of heating cable are to be identified as follows to indicate voltage:

  • Yellow - 120V
  • Blue - 208V
  • Red - 240V
  • Brown - 277V
  • Orange - 480V

Intrinsically safe systems are permitted in hazardous (classified) locations because they are made up of intrinsically safe circuits in which any spark or thermal effect is incapable of causing ignition under specified conditions. Furthermore, such circuits are isolated by an intrinsic safety barrier that prevents, under fault conditions, non-intrinsically safe energy levels from being applied to the hazardous environment that is meant to be protected.

Intrinsically safe terminals and wiring must be identified, both within the classified area and outside of it to ensure it will not be inadvertently energized to a higher level. Such identification is permitted to be light blue where that color is not already in use. Light blue also is used to identify raceways, cable trays, and junction boxes provided they contain only intrinsically safe wiring. Per the Code, raceways, cable trays, and other wiring methods shall be identified so that they may be readily traced throughout the installation. Labels with the wording “Intrinsic Safety Wiring” or equivalent are to be spaced not more than 25 feet apart. Although not required, the use of light blue raceway material and light blue enclosure covers would provide a superior installation.

As for fire alarm circuits, identification requirements are less stringent, because a high level fault would not cause an immediate explosion — just a supervisory trouble alarm (Photo 5). They are to be identified at terminal and junction box locations to prevent interference with the signaling circuit during testing and servicing. Though not NEC mandated, industry practice is to color enclosure covers red. The use of red raceways throughout makes future maintenance easier.

Sensitive electronic equipment feeders and branch-circuit conductors are required to be identified at all splices and terminations. Use of color is suggested. Whatever means of identification is used, it is to be posted at all branch-circuit panelboards and disconnects.

In health-care facilities, isolated power systems are made up of power circuits typically supplied by isolation transformers whose secondaries are ungrounded. The color code for isolated conductor Number One?is orange and for Number Two is brown. Where a third conductor is needed for a 3-phase system, it is yellow.

These are the principal color code schemes. Others mentioned in the Code are mobile home power supplies, park trailer power supplies, trailing cable, marina hoists, and cranes. Details for these particular installations can be found in Chapter 5 of the NEC.

Herres is a licensed master electrician in Stewartstown, N.H.