What does the "3" in 12/3 NM represent in electrical wiring?

In electrical wiring, the notation "12/3 NM" refers to a type of non-metallic sheathed cable that is commonly used for residential and light commercial electrical installations. The "12" in this designation indicates the gauge of the conductors, specifically that the wire is 12-gauge, which is an important factor in determining the amount of current the wire can safely carry.

The "3" represents the number of conductors included in the cable, excluding the ground wire. In this case, the three conductors are typically one hot wire, one neutral wire, and one additional hot wire, which allows for configurations such as a split-phase circuit or a multi-wire branch circuit. This is significant because it directly impacts the circuit's capacity for load and the variety of circuits that can be created from that single cable run.

Understanding this notation helps electricians determine the appropriate wire size and type for a specific application based on the expected load and safety requirements.