In the United States, what circuit does black wire insulation indicate in a three-wire 120 V AC cable?

In United States residential AC wiring, standard color codes are strictly used to ensure safety. The black wire is designated as the 'hot' or ungrounded conductor, which carries the alternating current from the source to the load. The white wire is used for the neutral (grounded) conductor, returning the current back to the source. The bare, green, or green-with-yellow-stripes wire is used for the equipment ground, which acts as a safety path for faults. It is critical to learn this standard for station safety when wiring AC equipment. Never assume wire colors are correct without testing with a multimeter, but black is the universally recognized US standard for 'hot'.