I’m looking at some electrical cable run on the subfloor, behind kitchen cabinets. I can call out the NEC as the subfloor is less than 1 1/4", thus someone could in theory put a screw in from below and hit the wire. Can I do better?
Technically according to code this could be citeable . It depend on the highly subjective “subject to physical damage” definition. However someone could also use a 3" screw in a wall and create an issue even with the cable setback the proper distance. How many times is something screwed to the underside of the flooring? I have had to run cables in the manner and never worried about it.
I have posted some sections below, but you will see that even though the concept of setback is required some do not apply as the cable is not through bored holes. A section similar to this was added recently regarding wiring under a corrugated roof deck to maintain clearances.
From the 2011 NEC.
300.4 Protection Against Physical Damage. Where subject
to physical damage, conductors, raceways, and cables
shall be protected.
(A) Cables and Raceways Through Wood Members.
(1) Bored Holes. In both exposed and concealed locations,
where a cable- or raceway-type wiring method is installed
through bored holes in joists, rafters, or wood members,
holes shall be bored so that the edge of the hole is not less
than 32 mm (11⁄4 in.) from the nearest edge of the wood
member. Where this distance cannot be maintained, the
cable or raceway shall be protected from penetration by
screws or nails by a steel plate(s) or bushing(s), at least
1.6 mm (1⁄16 in.) thick, and of appropriate length and width
installed to cover the area of the wiring.
(2) Nonmetallic-Sheathed Cable and Electrical Nonmetallic
Tubing. Where nails or screws are likely to penetrate
nonmetallic-sheathed cable or electrical nonmetallic tubing,
a steel sleeve, steel plate, or steel clip not less than 1.6 mm
(1⁄16 in.) in thickness shall be used to protect the cable or
tubing.
334.17 Through or Parallel to Framing Members. Types
NM, NMC, or NMS cable shall be protected in accordance
with 300.4 where installed through or parallel to framing
members. Grommets used as required in 300.4(B)(1)
shall remain in place and be listed for the purpose of
cable protection
334.15 Exposed Work. In exposed work, except as provided
in 300.11(A), cable shall be installed as specified in
334.15(A) through ©.
(A) To Follow Surface. Cable shall closely follow the surface
of the building finish or of running boards.
(B) Protection from Physical Damage. Cable shall be
protected from physical damage where necessary by rigid
metal conduit, intermediate metal conduit, electrical metallic
tubing, Schedule 80 PVC conduit, Type RTRC marked
with the suffix -XW, or other approved means. Where passing
through a floor, the cable shall be enclosed in rigid
metal conduit, intermediate metal conduit, electrical metallic
tubing, Schedule 80 PVC conduit, Type RTRC marked
with the suffix -XW, or other approved means extending at
least 150 mm (6 in.) above the floor.
Type NMC cable installed in shallow chases or grooves
in masonry, concrete, or adobe shall be protected in accordance
with the requirements in 300.4(F) and covered with
plaster, adobe, or similar finish.