National Electrical Installation Standards

Standards as High as Your Own

Tuesday, October 12, 2021


Greetings CQD,

Can I use black and white conductors (12 AWG THWN) for 120-volt receptacle circuits installed in an operating room? I have an inspector telling me I have to use brown and orange. The receptacle outlets are 125-voly, 20 ampere, single phase and are supplied from an isolated power system that supplies just the operating room receptacles. Your opinion would be appreciated.


Joseph Franks



Hello Joe,

The inspector is referring to the branch circuit wiring requirements in Section 517.160(A)(5) which indicates that isolated circuit conductors be identified as follows: Isolated Conductor No. 1 — Orange with at least one distinctive colored stripe other than white, green, or gray along the entire length of the conductor (2) Isolated Conductor No. 2 — Brown with at least one distinctive colored stripe other than white, green, or gray along the entire length of the conductor For 3-phase systems, the third conductor shall be identified as yellow with at least one distinctive colored stripe other than white, green, or gray along the entire length of the conductor. Where isolated circuit conductors supply 125-volt, single-phase, 15- and 20-ampere receptacles, the striped orange conductor(s) shall be connected to the terminal(s) on the receptacles that are identified in accordance with 200.10(B) for connection to the grounded circuit conductor. This is a case where Section 90.3 is in play relative to Chapter 5 requirements modifying the general requirements in Chapters 1 through 4, in this case to be more restrictive. Also thee installation instructions often specify the type of conductor insulation and colors for identification, so Section 110.3(B) is applicable relative to use of installation instructions. Hope this is helpful. 

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