National Electrical Installation Standards

Standards as High as Your Own

Monday, March 13, 2023


Good morning, Code friends. I am working on an office renovation project where the ceiling grid and lighting is being replaced. The lighting we are installing utilizes a switch device that has line (Class 1) voltage to the switch, but also 0-10V (Class 2) wiring for the dimming. The manufacturer is telling me I can wire both circuit in the same raceway and box if I use THHN 600V conductors. This does not sound right to me. Would this be permitted in the 2020 NEC®? All the best, Jack



Hello Jack, yes, under certain conditions. On the surface the Code prohibits us from installing Class 2 & 3 circuits in the same raceway as Class 1 circuits, but Section 725.130, Exception No. 2 allows a Class 2 or 3 circuit to be reclassified into a Class 1 circuit. This reclassification is done by using a Class 1 wiring method (any of the NEC® Chapter Three wiring methods would be acceptable), but then you must also remove any identifying markings indicating the circuit was a Class 2 or 3 circuit. Once this reclassification is done, the newly reclassified circuit must now be treated as Class 1 circuit regardless of the power source.

So back to the dimming circuit, by reclassifying the Class 2 dimming circuit as Class 1 circuit, you are now able to run the dimming circuit in the same raceway as Class 1 power circuit. Couple things to keep in mind. The newly reclassified Class 2 dimming circuit is a Class 1 circuit now, and as such must be wired as Class 1 circuit in its entirety. It must also be kept separated from other Class 2 and 3 circuits per Section 725.136. 

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