Q. What are the rules related to the installation of conductors from different voltage systems — such as 120V, 208V, 240V, 277V, and 480V — in the same raceway or enclosure?
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A. If the premises wiring system contains branch circuits supplied from more than one voltage system, each ungrounded conductor must be identified by phase and system at all termination, connection, and splice points in accordance with Sec. 210.5(C)(1)(a) and (b) [210.5(C)(1)]. Identification can be by color coding, marking tape, tagging, or other means approved by the authority having jurisdiction [210.5(C)(1)(a)]. The method of identification must be documented in a manner that’s readily available or permanently posted at each branch circuit panelboard [210.5(C)(1)(b)].
When a premises has more than one voltage system supplying branch circuits, the ungrounded conductors must be identified by phase and system. This can be done by permanently posting an identification legend that describes the method used, such as color-coded marking tape or color-coded insulation.
Conductors with insulation that’s green or green with one or more yellow stripes can’t be used for an ungrounded or neutral conductor [250.119]. Although the NEC doesn’t require a specific color code for ungrounded conductors, electricians often use the following color system for power and lighting conductor identification:
• 120/240V, single-phase — black, red, and white
• 120/208V, 3-phase — black, red, blue, and white
• 120/240V, 3-phase — black, orange, blue, and white
• 277/480V, 3-phase — brown, orange, yellow, and gray; or, brown, purple, yellow, and gray
Power conductors of alternating-current and direct-current systems rated 1,000V or less can occupy the same raceway, cable, or enclosure if all conductors have an insulation voltage rating not less than the maximum circuit voltage [300.3(C)(1)].
