Identify the type of cable that is permitted in single- and multifamily dwelling units but that cannot be used underground, nor in buildings that are more than three stories above grade, nor in commercial garages, motion picture studios, theaters, places of assembly, elevator hoist ways, and other corrosive or hazardous locations, and what electrical code is universally used in the United States?
The Correct Answer and Explanation is :
The type of cable that meets these restrictions is Nonmetallic-Sheathed Cable (NM Cable), commonly known as Romex® (a brand name). The electrical code universally used in the United States is the National Electrical Code (NEC), published by the National Fire Protection Association (NFPA 70).
Explanation:
Nonmetallic-Sheathed Cable (NM Cable) is widely used in residential electrical wiring for single-family and multifamily dwellings. It consists of two or more insulated conductors and a bare ground wire, all encased in a nonmetallic, moisture-resistant sheath. However, the NEC imposes several restrictions on NM Cable usage, ensuring safety in various environments.
- Permitted Uses:
- NM Cable is allowed in residential buildings, particularly single-family and multifamily dwellings up to three stories above grade.
- It is used for interior wiring in walls, ceilings, and attics where it is protected from physical damage.
- It is cost-effective, easy to install, and commonly used for branch circuits supplying outlets, lights, and appliances.
- Prohibited Uses:
- Underground Installations: NM Cable lacks moisture and corrosion resistance, making it unsuitable for direct burial or wet locations.
- Buildings Over Three Stories: The NEC restricts NM Cable to buildings no taller than three stories, requiring fire-resistant wiring methods (e.g., conduit or MC Cable) in taller structures.
- Commercial Garages, Theaters, and Assembly Areas: These locations pose fire and mechanical damage risks, necessitating more robust cable protections.
- Elevator Hoistways and Hazardous Locations: NM Cable is not permitted due to vibration, chemical exposure, and fire hazards.
The National Electrical Code (NEC) is the authoritative standard for electrical installations in the U.S., ensuring safety and consistency across all jurisdictions. It is updated every three years, with the latest version governing wiring practices nationwide.