National Electrical Installation Standards

Standards as High as Your Own

Tuesday, February 28, 2023


Hi Charlie and thank you for continuing this great resource. We recently had an inspection on a small commercial office remodel project. The service providing power to the building is an 1200A, 120/208V service. We installed a 50kVA, P-120/208V to S-277/480V transformer for the lighting. During the final inspection, we were cited because we used the following color coding:

  • 120/208: A-BLK, B-RED, C-BLUE, N-WHITE

The Inspector stated that we are not allowed to use White and Gray for the two different system Neutral Conductors. Basically, citing that gray and white are the same color and there needs to be more of a differentiation than just those two colors. I have never heard this before and using this color coding has been common practice for years. What has changed? What am I missing? Thanks, Adam Dassow.



Hi Adam, there are a couple things at play here.

Section 210.5(C) requires anytime a building has two nominal voltages present you must establish two separate color codes, and then keep them consistent throughout the entire building.

The requirement for the Neutral conductor the inspector is referencing, only comes into play if circuits/feeders from both systems are in the installed in the same raceway, cable, box, or auxiliary gutter. NEC 200.6(D) states when this mixing of system conductors exists, the methods of identifying the Grounded/Neutral conductor cannot solely rely on one Grounded/Neutral Conductor being White, and the other being Gray.

The reasoning behind this rule is, a White conductor will get dirty, and discolored over time, starting to look Gray. So additional marking must be in place, like a trace color (other than green) on the White or Gray insulation. Again, this rule only applies if the branch circuits and feeders from both systems are present in the same raceway, cable, or box etc.

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CHARLIE TROUT: Charles M. Trout, better known as Charlie, was a nationally known NEC® expert and author. He served on several NEC® technical committees and is past chairman of CMP-12. In 2006 Charlie was awarded the prestigious Coggeshall Award for outstanding contributions to the electrical contracting industry, codes and standards development, and technical training. Even though Charlie passed away in October of 2015, his work continues in spirit. NECA continues to maintain this question forum for its many subscribers in memory and recognition of all his significant contributions to making the NEC what it is today.

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