Chart of the possible wire functions for two-wire and three-wire cable (14-2, 12-2, 14-3, 12-3). This chart will apply below to the diagrams (Fig.1-7) and all their Commentary, and to the Cable-and-Box Chart below that. New window.
The status or intended function of each insulated wire in any cable will be one of these:
Hot =live =being 120 volts in relation to ground =able to shock
The chart shows us that any two-wire cable in your home can be given one of four names, according to the combination of its black-wire and white-wire functions. All three possible combinations of the first three functions -- hot, neutral, switched -- have their cable-names. I suppose theoretically a cable could have one wire be hot or neutral and the other be a traveler, but this is never really done. Since the travelers are needed as a pair, they have their own cable: "x". Its nickname is not established. By the function of its wires, it could be called a traveler cable or a 3-way cable.
Neutral =grounded white wire for carrying circuit current back to the source
Switched =hot only at times (when switch is "closed")
Traveler =a particular switched (hot at times) wire that is to be hot when its partner-traveler is not
Dead =neither hot nor grounded =floating =what a switched wire is when it is not hot
(No always-dead wire is shown in the chart because the chart is to show functions, not lack of function.)
Likewise, we can designate five wire-uses possible within three-wire cables. We do not have to divide the 3-way switching cables -- "n" and "t" -- into separate categories, the way I have done. However, the most common 3-way/4-way wiring does have a neutral accompany the travelers, and since the neutral must be white, the travelers' colors are determined. In contrast, the wires of an n-cable have more color leeway because by definition no wire is a neutral in them.
Other notes: The use of red as a switched wire in f-cables is only conventional, not a matter of house wiring color Code... The two hot wires in a d-cable are supposed to be 240 volts apart from each other, which is set up by how their two breakers are arranged in the panel. These hots are still each 120 volts in relation to ground.
As you can see, in any cable the only reliable meaning that wire color will have is: reds and blacks will not be neutrals.
Realize too that, in spite of its intended function or tested characteristics, a wire's actual status can change. Any switched wire is an example of this already, being hot or dead at the whim of the switch. But in addition the failure, undoing, or misconnection of wires at one point along a circuit can make some other wires lose their intended character. A "neutral" could become hot. A hot could become switched or dead. Since these disconnections and misconnections are exactly what you may be involved in solving, until they are all solved, you will need to watch your wire-identity assumptions closely.