Wiring Methods & Practices


Thread Starter

Jack Reyes

NFPA 79 States that black ungrounded line, load, and control conductors at line voltage should be black while ac control conductors, at less than line voltage should be red.

We have an electrician that insists that only the 120Vac comming into the cabinate should be black but once it hits a fuse and continues on to a device the wire should be red.

His interpetation is that line voltage is a term that only applies conductors comming into the control cabinate. I always thought that any conductor that was at the same potential as the line voltage should be black.

Can someone please clear this up for me?

Kirk S. Hegwood

I maybe wrong but the only colors the NFPA 79 have mandatory are ground (green or green w/ yellow stripe) and grounded conductors (white or lt. Gray). We've always practiced similar to what your electrician is following. In a control panel, black is always power (120, 240, 480), but control power once it is broken by a relay or some switching device (plc) changes to red.

In the field, we've always practiced Brown, Orange and Yellow as 480V, Black, Red and Blue for 240V.

I believe it is somewhat arbitrary other than the ground and neutral.

Kirk S. Hegwood
Signing for Hegwood Electric Service, Inc.
[email protected]
Jack this is directly from NEMA Standard ICS-1-2000. It outlines the NEMA standard for wire colors.
Hope it helps
Mark Massa

7.6 Color coding of wiring
Where wired with thermoplastic insulated wire and where NEMA standard color coding is specified, the color code for Industrial control wiring shall be:
a. Line and load circuits (AC and DC), power and motor circuits - black
b. Control circuits
1. AC - red
2. DC - blue
c. Connection to primaries of control transformers - black
Color coding, where specified, applies to the wiring between devices that are interconnected to form a control assembly and not to the wiring which is an integral part of the devices. Where solenoids, brakes, and similar devices are employed as a part of the controller system, the panel wiring shall be color coded in the same manner as the power circuits. However, the panel wiring shall be color coded in the same manner as the control circuit where solenoids, brakes, and similar devices are either:
a. Operated at line voltage and fused by control-circuit fuses
b. Operated from a voltage lower than the line voltage.
The colors green and white have been recognized in equipment and distribution circuit work. Green usually indicates an equipment grounding conductor, and white indicates the grounded neutral conductor of the circuit.
7.7 Markings of coils
Coils that are applied at their continuous ratings on single coil devices shall contain the following minimum information:
a. Rated voltage;
b. Rated frequency (for AC coils),"DC" (for DC coils);
c. Manufacturer's name or trademark;
d. Manufacturer's ordering number.
It is recommended that the coils be so mounted that the manufacturer's ordering number will be visible when the coil is in place on the device.
Supply voltage wiring (120vac) to an instruction processor (plc or pc) should be black. Discrete input and output wiring (switches, coils,
etc..) should be red if 120vac, or blue if 24,12 or 5vdc.
The rules we follow at our panel shop are 208vac and above is to be black,120vac hot and controls are red and nuetral is white, 24vdc is to be blue both pos and neg or neg can be white with a blue stripe, 25vac is to be brown and blue with a white stripe. Now I don't think there is a writen standard for color coding, when I worked construction 480/460 went like this L1 brown L2 yellow and L3 orange if it was 480/277 the nuetral was to be grey. If it was a 208/120v system the incomong line was to be L1 black L2 red and L3 blue and nuetral is white. This designated the phasing incase parallel lines were run.
Good luck making sense of it I think you can make your own plant standard if you would like just dont make green one of you hot conductors.
Your electrician is correct, unless the plant line voltage is actually at 120 VAC (not likely). And you are correct that NFPA-79 does specify these colors. But the scenario you give is one that sometimes gives us trouble as well. What we have settled on, and has been accepted by our customers, who are typically automotive, is this: If the enclosure in question is
essentially an extension (i.e. has no disconnecting means of its own) of another enclosure that contains the disconnecting means for this enclosure, then red wiring is appropriate as the 120 VAC feed. Some of our customers ask us to use yellow or red with yellow stripe in this case IF the disconnecting means is not in the line of sight of the enclosure.

If the enclosure in question does have it's own disconnect, we treat ANY 120 VAC signals, even the feed to that disconnect, as interlock wiring. As such it is yellow (or orange if in Europe).

Hope this helps and happy holidays to all!
Jim Mooney

Roderick K. Duet

In the instance of a field device input, a prox. for example, the 120VAC or 24vdc line side of the switch is fed from the 120VAC or 24vdc source, our practice has always been to denote them as black and blue respectively, the switch leg has and always will be red and orange respectively. This way when a plant engineer pulls a switch apart he knows which leg of it is hot. I know you safety extreme people just had goose pimples, but welcome to the real world. I can't count the times I've had to work it HOT so the system can keep running.
You are absolutely right about the need for "hot" work. If this task was totally barred, productivity would drop by at least 20%.

Bob Pawley