Type NM cable is stapled to wood studs during a dwelling remodel. What is the maximum support interval, and what is the maximum distance from an outlet box at which the cable must be secured?
- Supported every 4-1/2 feet and secured within 12 inches of the box
- BSupported every 6 feet and secured within 12 inches of the box
Six feet is the support interval for MC cable, not for nonmetallic sheathed cable.
- CSupported every 3 feet and secured within 8 inches of the box
The 8-inch figure belongs to the special case of a single-gang nonmetallic box without internal clamps, and 3 feet is not the general support interval for this cable.
- DSupported every 10 feet and secured within 3 feet of the box
Ten feet and 3 feet are the numbers for rigid metal raceways such as EMT. Cable requires far tighter support.
Why A is correct
Nonmetallic sheathed cable carries no mechanical load of its own, so the support intervals exist to keep the jacket from being stretched and to keep pulling strain off the box connection. NEC 334.30 sets 4-1/2 feet along the run and 12 inches from each box for exactly that reason: the last staple is what absorbs a tug on the cable instead of the clamp or the terminal screws.
What this question is testing
This item tests recall of the general securing and supporting numbers for nonmetallic sheathed cable and awareness that a different distance applies at nonmetallic boxes without clamps.
On the job
Rough-in inspections in residential work turn on this rule more than any other. Inspectors count staples across a wall and check the first staple above every box. Drooping cable between joists also gets flagged, and cables running across the bottom of floor joists must be protected or run through bored holes. Keeping a staple within a foot of every box and roughly every 4 feet along the run makes the walkthrough painless.
Memory technique
A foot off the box, and four and a half between staples.
Exam tip
Twelve inches from the box and 4-1/2 feet along the run covers NM, AC, FMC, and LFMC alike.
Where to look it up
Look at the .30 section of the nonmetallic sheathed cable article, and read the subsection that addresses nonmetallic single-gang boxes.