CSLB C-10 Electrical ContractorWiring Methods and MaterialsEasy
A homeowner is having new branch circuits installed inside the wood-framed walls of a single-family dwelling in a dry, unexposed location. Which cable type is most commonly specified for this concealed interior wiring?
- AType NM-B cable
- BType UF cable
- CType AC cable
- DType MC cable
Show answer & explanationAnswer & explanation
Correct answer: A. Type NM-B cable
Type NM-B (nonmetallic-sheathed) cable is the standard cable used for concealed dry-location wiring in dwellings per NEC Article 334. UF is rated for wet/underground use, and MC/AC are metal-armored cables typically used where extra mechanical protection is required.
Why the other options are wrong
- B. UF is rated for wet and underground locations, unnecessary here.
- C. AC cable is armored and used where impact protection is required, not standard interior wiring.
- D. MC has a metal sheath and is used where more mechanical protection is needed, not the typical dry-wall choice.
NM-B Cable
Nonmetallic-sheathed cable approved for concealed dry-location wiring in dwellings, consisting of insulated conductors plus a bare equipment grounding conductor inside a plastic jacket.
- Governed by NEC Article 334
- Limited to dry locations unless rated NM-B for damp per listing
- Not permitted in commercial high-rise or exposed to physical damage without protection
Memory trick: 'N' for Normal dry homes = NM-B.