What is the minimum size of nonmetallic sheathed cables that may be secured directly to the lower edges of joists in unfinished basements?

The minimum size of nonmetallic sheathed cables that may be secured directly to the lower edges of joists in unfinished basements is 6 AWG. This is based on the National Electrical Code (NEC), which provides guidance on the allowable sizes and installation practices for various types of electrical wiring in different environments.

Using 6 AWG ensures that the cable can handle the expected load while providing adequate protection against overheating and electrical hazards. Nonmetallic sheathed cables, commonly referred to as NM cables, are designed to be flexible and easy to install in various residential applications, including basements. In unfinished basements, securing the cables to the lower edges of joists is an acceptable practice as long as they meet the NEC requirements regarding size and securing methods.

Other sizes, such as 4 AWG, 8 AWG, and 10 AWG, do not meet the NEC guidelines for this specific installation, either being too large or too small for the applications permissible in such conditions. The guidelines aim to balance safety, functionality, and adherence to code. Thus, recognizing the importance of using the correct gauge ensures compliance and enhances safety in electrical installations.