Color Coding Changes: NEC 2020 impacts 0–10V control wiring

Published On
Dec 15, 2021

Per a change in the 2020 National Electrical Code effective Jan. 1, 2022, 0–10V (Class 2) dimming wire insulation colors have changed to eliminate use of any reserved colors, notably gray. The National Electrical Manufacturers Association (NEMA), Arlington, Va., responded with an industry guideline adopting pink as a substitute. Here, I discuss the color change and then take a quick look at the cost-effectiveness of 0–10V versus digital dimming.

Color change

According to the 2018 Commercial Buildings Energy Consumption Survey, multilevel lighting and dimming is used to control lighting in an estimated 15% of commercial building floorspace. In these applications, 0–10V continues to serve as a workhorse dimming method, only growing more popular as dimming becomes far more widely adopted with LED than it did with its predecessor, fluorescents. With this dimming method, the control wires are used as a circuit for a low-voltage signal that communicates dimming intensity.

For many years, industry convention for 0–10V control wiring was to use one purple and one gray insulated conductor to designate conductor pairs for connecting luminaires, drivers and control devices in a 0–10V dimming control circuit. These colors are easily identified on wiring diagrams, installation instructions and dimmable driver/ballast labeling.

In the 2020 NEC , Article 410.69 disallows use of insulation colors reserved for the grounded branch circuit conductor (white or gray) or the equipment grounding conductor (green or green with a yellow stripe) for control circuit conductors connected in the field. This change minimizes potentially hazardous miswiring.

In response, NEMA’s Wire & Cable Section and Lighting Systems Division jointly decided on pink as an acceptable substitute for gray as a 0–10V conductor color, formalizing this guideline in the April 2021 Publication 100-2021, “Wire Insulation Colors for Lighting Systems.”

As a result, manufacturers adhering to the NEMA guideline and supporting compliance with the 2020 NEC will provide 0–10V control wiring with a violet (purple) conductor and a pink conductor, which are discernible as standardized CIE colors. While the NEMA guidance is not code, it provides the industry with consistency.

As the NEC change requires manufacturers to make significant revisions to their labeling and literature, NEMA encouraged the industry to act expeditiously to prepare for the Jan. 1, 2022, effective date. To facilitate compliance during the transition, the 2020 NEC allows permanent re-identification of gray control conductors (where visible and accessible) by installers using marking tape, painting or other effective means.

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Is 0–10V always more economical?

Due to its familiarity and cost-effectiveness, 0–10V, traditionally used with fluorescent dimming, is now very popular for LED dimming. For connected lighting systems, digital wiring offers an alternative with solid utility, but a typically higher luminaire cost has limited adoption in favor of 0–10V. In a contribution to the Lighting Controls Association website published October 2021, consultant C. Webster Marsh challenged the popular assumption that 0–10V is more cost-effective, saying, “It depends.”

“Just because 0–10V dimmed luminaires are cheaper than digitally dimmed luminaires, it should not be assumed there will be a lower price tag on the overall project,” he wrote.

In a nutshell: while 0–10V drivers require a remote switch such as a relay, dedicated switched circuit per control zone, and a pair of control wires per control zone, a majority of digitally dimmed luminaires allow the luminaire to act as its own control zone and relay without requiring additional equipment or wiring.

“What it boils down to is how many luminaires and zones are on the project,” Marsh said. “The greater the number of luminaires and zones the project has, the better equipped digital dimming is to provide a more cost-effective solution. A corridor with just one zone may be cheaper with 0–10V dimming, but a large open office may cost less if the luminaires are dimmed digitally.”

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