NM-B cable: 14/2 through 6/3, coils and cut lengths

Two or three conductors under a PVC jacket

NM-B is a factory assembly of two, three or four insulated conductors plus a bare equipment ground, all wrapped in a flame-retardant PVC jacket and filled to a round or flat profile. It is a 600-volt cable for dry locations, run through stud bays, joist spaces and attic floors, secured with staples and protected by nail plates where it passes close to a framing face.

The conductors are rated 90°C, but the cable is applied at the 60°C ampacity column, which is why a 12 AWG NM-B circuit is a 20-amp circuit and not more. That limitation is printed nowhere the seller will see, and it is the reason an inspector asks for the jacket print rather than accepting a size from memory.

Reading the size: 14/2 through 6/3

The first number is the conductor gauge and the second is the count of insulated conductors, ground excluded. So 14/2 is two 14 AWG conductors plus a bare ground, and 12/3 is three 12 AWG conductors plus ground. The common residential set runs 14/2 for lighting, 12/2 for receptacles and kitchen circuits, 10/2 and 10/3 for dryers and air handlers, and 6/3 for ranges and service feeds to outbuildings.

The larger sizes are where the money and the weight sit, and where partial coils are most common. A 6/3 range run takes thirty-five feet out of a fifty-foot coil, leaving fifteen. A 10/3 dryer run leaves more. Those remainders are numerous and individually small, and they are the reason a residential contractor's shelf looks the way it does.

Why partial NM-B coils accumulate

Retail packaging drives it. Big-box coils come in 25, 50, 125 and 250 feet, and a job that needs eighty feet buys a hundred and keeps twenty. Over a season a three-man crew builds a shelf of these, each coil banded with its own tag, none long enough for the next job and none short enough to throw away.

Then there is the removed cable. A kitchen remodel pulls old NM-B out of the walls, and it comes out in short kinked runs with staples still in it. That material is a different thing from a coil: the jacket is deformed, the conductors are work-hardened, and the length is whatever the wall allowed.

How a partial coil is judged

Two things separate a resaleable coil from scrap: the print and the condition. The jacket print gives the size, the type and the listing, and it survives most handling. Sun is the enemy, since NM-B is not sunlight rated and a coil left on a truck bed through a summer goes brittle and fades. Staples and pulled bends are the second enemy.

• Size and conductor count from the jacket print
• Remaining length measured, or the original coil length stated
• Whether the coil is still in its retail band and tag
• Jacket condition: brittle, faded, stapled or kinked
• Removed cable kept apart from unused coil stock