Wire colors

The color for wire insulation is clearly described in the National Electrical Code and is an important part of the electrical installation.  The colors of the wire insulation help to identify the purpose and usage of the wire.  Using a wire with the wrong color insulation is a sign of very poor workmanship and it can cause someone down the road to treat that wire as though it had a different purpose.  This might lead to a very unsafe condition.

Grounding wires – wires that don’t normally carry any electrical current – must have green insulation or green with a yellow stripe.  Some grounding wires can be bare copper with no insulation at all.

So if a green wire is connected to a circuit breaker – meaning that it’s being used as hot conductor (or as the NEC call it an “ungrounded conductor”) then someone downstream might see this green wire, think it’s a grounding wire, and do something with it that makes the whole system unsafe, maybe injuring the person doing the work.  This is a terrible situation.

Neutral wires (or as the NEC calls them “grounded conductors”) must have white or gray insulation or have three continuous white or gray stripes over another color (but not green).

This is all pretty simple for small wire sizes, but for large sizes of wire it can be hard (or just impossible) to get wire with green or white insulation.  So there are some rules for marking a differently colored large wire with green or white tape to identify it as a grounding or neutral wire.

Hot wires (“ungrounded conductors” as per the NEC) – connected directly to the circuit breakers – can be pretty much any other color except white, gray, or green.  Black is the most common color, but red is very common also.  Other common colors for hot wires include blue, yellow, purple, brown, and orange.  This is all pretty basic for a normal residential system consisting of a single phase 120/240 volt system, but there are different rules and conventions used for 3-phase systems and for systems using higher voltages.

As noted above with larger sizes of grounding and neutral wires, there are some times when you are allowed to reidentify a wire – to mark the ends of the wire with different colors of tape to reidentify the wire as having a different purpose than its color would indicate.  Many 240-volt circuits don’t use a neutral wire but instead use two hot wires.  This kind of circuit is often installed using a cable that comes as a manufactured assembly of three wires – black, white, and green (or bare).  If you want to use this cable for a 240-volt circuit then you can reidentify the white wire with some black electrical tape at both ends of the cable, to identify the wire as now being used as a hot wire.

In the Chicagoland area most residential systems include metal conduit with separate wires pulled through the conduit tubing.  It’s never acceptable to reidentify a white neutral wire that runs through conduit.  You can only reidentify a white neutral wire that’s part of a cable assembly.

To recap:

• Green is grounding
• White or gray is neutral
• Anything else is hot
• Doing anything else can lead to problems down the road and is unsafe and a sign of poor workmanship.

Like most everything in the National Electrical Code there are exceptions.