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NM Cable Support, Protection, and Clearance Rules

Reference ServiceDelivery Updated Oct 28, 2026 ยท Electrical

Why this matters

Rough-in inspections fail on NM cable for a short list of reasons: a staple too far from a box, a hole drilled too close to the face of a stud with no plate, a cable stapled across the bottoms of basement joists, a run across an attic floor beside a scuttle with no guard strips. Each is cheap to get right before the drywall and expensive after, because the failure that inspection is guarding against is a drywall screw or a homeowner's boot finding the cable years later. This card is the support and protection rules for NM cable with the reason each distance exists. The attic and basement routing HowTo applies them run by run.

Support: within 12 in of the box, then every 4-1/2 ft

NEC 334.30, 2023 edition (2020 where the section moved), as adopted by your jurisdiction: NM cable is supported and secured by staples, cable ties, straps, hangers or similar fittings designed and installed so they do not damage the cable, at intervals not exceeding 4-1/2 ft, and within 12 in of every cable entry into an enclosure such as an outlet box, junction box, cabinet or fitting.

VERTICAL DROP INSIDE A STUD BAY (side of stud)
  TOP PLATE    ==========   hole through plate, see
                    |       the setback rule below
                    S  <- staple
                    |
                    |  <- 4-1/2 ft maximum between
                    |     staples on the run
                    S  <- staple 12 in or less
                    |     above the box
                [ BOX ]

The rules that sit around that distance:

  • Bored holes count as support on horizontal runs. 334.30(A), in substance: a cable run horizontally through holes or notches in framing members spaced no more than 4-1/2 ft apart is considered supported and secured. A cable running through every stud at 16 in on center needs no staples between studs; it still needs one within 12 in of the box it ends in.
  • The 8 in exception at a small nonmetallic box. 314.17, as adopted, in substance: where a single-gang nonmetallic box of the size it describes has no cable clamp, the cable must be secured within 8 in of the box, measured along the sheath, with at least 1/4 in of sheath inside the box. Most new-work plastic boxes are clampless, so in practice 8 in is the number at a single-gang plastic box and 12 in everywhere else.
  • Fished cable is exempt. 334.30(B)(1): cable fished through concealed spaces in finished buildings, where support is impracticable, may be unsupported. That exemption covers old work only, not a new wall left open.
  • Flat cable is not stapled on edge. 334.30 says it in so many words. A staple driven over 12/2 standing on edge pinches one conductor against the other.
  • Staples are snug, not crushing. A staple driven until the jacket bulges has damaged the cable the support rule exists to protect. One cable per staple unless the staple is listed for more and for the cable size.

Protection in framing: the 1-1/4 in setback

300.4(A)(1), as adopted, in substance: where a cable runs through a bored hole in a wood framing member, the edge of the hole is not less than 1-1/4 in from the nearest edge of the wood member. Where that distance cannot be kept, the cable is protected by a steel plate or bushing at least 1/16 in thick, of appropriate length and width, covering the area of the wiring. Listed steel plates thinner than 1/16 in are permitted where listed and marked to give equal or better protection.

2x4 STUD CUT ACROSS: 3-1/2 IN FACE TO FACE
FACE A                                        FACE B
|<--- 1-1/4 --->|<--- 1 IN HOLE --->|<--- 1-1/4 --->|
  wood to face      largest hole        wood to face
                    centered with
                    both edges legal
EDGE CLOSER THAN 1-1/4 IN TO A FACE: 1/16 IN STEEL
PLATE ON THAT FACE, OVER THE CABLE'S PATH

The arithmetic on a 2x4 is the whole story: 3-1/2 in of depth, less 1-1/4 in on each side, leaves 1 in. A 1 in hole drilled dead center is legal with no plate. A 1 in hole drilled 1/4 in off center leaves 1 in of wood on one side and needs a plate on that face. The distance is there for fasteners: a 1-1/4 in drywall screw through 1/2 in drywall reaches about 3/4 in into the stud, and trim nails and longer screws go deeper. A longer fastener does not change the code distance, so keep holes centered.

The same distance applies in other places, in substance:

  • Notches (300.4(A)(2)). A cable laid in a notch in a stud or joist is protected by a 1/16 in steel plate before the notch is covered, whatever its depth, and the notch must not weaken the framing (structural limits come from the building code as adopted, not the NEC).
  • Running along framing (300.4(D)). A cable run parallel to a stud, joist or rafter is kept at least 1-1/4 in from the nearest edge of the member where nails or screws are likely to penetrate, or protected by a plate. A cable stapled to the face of a stud where the drywall lands is the common violation.
  • Under roof decking (300.4(E)). Cables installed under metal-corrugated sheet roof decking are kept at least 1-1/2 in from the lowest surface of the decking, because roofing screws come through it. This is a light-commercial issue more than a residential one.
  • Steel framing (300.4(B)). Holes punched or cut through metal members carry a listed bushing or grommet that covers all metal edges, secured in the opening before the cable is pulled.

Attics: guard strips near the scuttle

334.23, as adopted, sends NM in accessible attics to the rule written for armored cable (320.23), in substance: where cables run across the tops of floor joists, or within 7 ft of the floor or floor joists across the face of rafters or studding, they are protected by guard strips at least as high as the cable. Where the attic is not accessible by permanent stairs or ladders, that protection is required only within 6 ft of the nearest edge of the scuttle hole or attic entrance. Cables run along the sides of rafters, studs or ceiling joists need no guard strips.

The logic is foot traffic. Where people walk, a cable lying across the joist tops gets stepped on, and in a pull-down-stair attic that is everywhere; in a scuttle-only attic it is the area inside reach of the hole.

Basements and crawl spaces: not across the bottoms of joists

334.15(C), as adopted, in substance: in unfinished basements and crawl spaces, where cables run at angles to the joists, cables smaller than two 6 AWG or three 8 AWG conductors are run through bored holes in the joists or on running boards. Larger cables may be secured directly to the lower edges of the joists. A 12/2 or 14/2 stapled across the bottoms of joists is the most common rough-in write-up in basements.

Where NM runs down an unfinished basement wall or anywhere exposed to physical damage, 334.15(B) requires protection, in substance, by rigid metal conduit, intermediate metal conduit, EMT, Schedule 80 PVC, or another approved means, with a nonmetallic bushing or adapter where the cable leaves the raceway. Schedule 40 PVC is not on that list for this purpose; check the wording of your edition.

Bundled cables through one hole

Three or more NM cables through one bored hole that will be sealed with caulk, foam or insulation trigger the ampacity adjustment in 334.80, as adopted, because the cables cannot shed heat; so do more than two such cables installed in contact with thermal insulation without spacing. Separately, cables stacked or bundled together for more than 24 in without spacing take the general adjustment in 310.15(C)(1). The factors are in 'Conductor Ampacity Reference'; the practical answer is to drill a second hole rather than pack five cables through one.

Worked example: a basement-to-bedroom run

A new 20 A circuit in 12/2 NM from a panel in an unfinished basement to a receptacle in a first-floor bedroom wall, with 2x10 floor joists at 16 in on center running perpendicular to the cable's path, and 2x4 studs.

Before drilling into finished walls or floors, know what is in them: a scanner pass and a look at the panel schedule, and the circuits in that area turned off and verified dead with a CAT III or better meter proven on a known live source before and after, per NFPA 70E Article 120 (120.5 in the 2021 edition, renumbered in 2024) and 29 CFR 1910.333(b)(2). Drilling overhead puts chips in your eyes, so safety glasses with side shields. In a house built before 1978, drilling or cutting painted plaster or trim can release lead dust: where the work disturbs more painted surface than the rule's minor repair and maintenance allowance, the EPA Renovation, Repair and Painting rule (40 CFR Part 745) applies to protect occupants, and worker protection follows the OSHA lead standard for construction (29 CFR 1926.62), including a respirator under a written 29 CFR 1910.134 program (applied to construction by 29 CFR 1926.103) where the exposure assessment calls for one. When the drilling is done, restore those circuits and confirm each outlet on them works.

  1. Across the joists. The cable crosses six joists between the panel and the wall. 12/2 is smaller than two 6 AWG, so it cannot be stapled to the joist bottoms; drill each joist. A 3/4 in hole at mid-depth of a 9-1/4 in joist leaves more than 4 in of wood on each side, well clear of 1-1/4 in, and within the building code's bored-hole limits for joists, as adopted. The holes are about 16 in apart, so the horizontal run is supported by them.
  2. Up into the wall. Through the bottom plate from below with a 3/4 in bit centered on the 3-1/2 in plate: each edge of the hole sits 1-3/8 in from a face (3-1/2 minus 3/4 is 2-3/4, halved). That clears 1-1/4 in, no plate needed.
  3. Across two studs to the box. The first stud gets a 1 in hole centered, 1-1/4 in of wood each side, legal. On the second stud the bit wandered: the hole's center ended up 1-1/2 in from the room-side face, so its near edge is 1 in from that face (1-1/2 minus 1/2). That is under 1-1/4 in, so a 1/16 in steel plate goes on the room side of that stud over the hole.
  4. Into the box. A clampless single-gang plastic box: staple 6 in from the box, under the 8 in exception, with 1/2 in of sheath inside the box past the knockout, more than the 1/4 in minimum. Each conductor leaves at least 6 in of free length, with at least 3 in outside the opening of a box this small (300.14).

What the inspector checks on that run, and what it shows: no cable on the joist bottoms; one plate, on the stud where the setback failed; a staple 6 in from the box. Leave the plate visible and the stud bay open until the rough-in inspection signs off.

And if a plate gets forgotten, the failure shows up later as a drywall screw through the cable: a breaker that trips the day the drywall is hung, or worse, a screw that nicks the insulation without tripping anything. If a circuit trips during drywall, the hangers stop, the circuit stays off, and the screw is found before the wall is finished.

References

  • NFPA 70, National Electrical Code, 2023 edition as adopted by your jurisdiction: 300.4, 300.14, 314.17, 320.23, 334.15, 334.23, 334.30, 334.80
  • NFPA 70E, Standard for Electrical Safety in the Workplace, current edition, Article 120; 29 CFR 1910.333(b)(2)
  • 40 CFR Part 745 (EPA Renovation, Repair and Painting); 29 CFR 1926.62 (lead in construction)
  • See related: How to Run NM Cable Through Attics and Basements; Conductor Ampacity Reference

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