UNIT 2.7 — WIRING METHODS

Cable types and wiring methods

CERT 2 · Residential Wiring · ~10 min

Community content — not verified by a licensed electrician. Lessons and questions here are written for study practice and pinned to NEC 2023. Code editions and local amendments vary by jurisdiction. Always confirm against your adopted code book and your licensing board's published exam outline before test day.

The cable marking tells you where it may legally live. NM (non-metallic sheathed, the familiar 'Romex') is the residential workhorse — dry, protected, indoor locations only. UF (underground feeder) has solid molded insulation and is rated for direct burial and wet locations. MC (metal-clad) has an interlocked armor and includes a grounding conductor. AC ('BX') uses the armor itself plus an internal bonding strip as the ground path.

Support and protection rules generate most of the exam questions. NM cable is secured within 12 inches of a box (8 inches for single-gang plastic boxes without clamps) and every 4½ feet thereafter. Where cable runs through studs, the hole must be at least 1¼ inches from the nearest edge; if that clearance is impossible, a 1/16-inch steel nail plate protects it.

Conductor color is not decorative. White may be re-identified as a hot in a switch loop by permanently marking it with black tape or paint at every visible point — but you may never re-identify a white as a hot in an ordinary branch circuit just to save a cable pull.

Exam focus: match cable type to location (NM = dry indoor, UF = buried), the 12-inch/4½-foot support rule, and the 1¼-inch stud clearance with nail-plate fallback.

Dry indoor only

Direct burial / wet

Support

12 in + every 4½ ft

Knowledge check

Quiz — 3 questions

1. Which cable is listed for direct burial?

2. NM cable must be secured within what distance of a box?

3. A hole bored through a stud is less than 1¼ in from the edge. You must:

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