What size wire gauge requires protection by a bushing when entering a box?

The requirement for using a bushing when entering a box is primarily focused on the protection of conductors from physical damage and ensuring proper electrical connections. According to the National Electrical Code (NEC), conductors that are larger than 4 AWG must have a bushing at the entry point of a box to protect the insulation from abrasion and to maintain the integrity of the electrical system. The bushing acts as a safeguard that ensures that the sharp edges of the box entry do not compromise the insulation of the wire, which could potentially lead to short circuits or electrical failures.

In this context, options related to sizes smaller than 4 AWG do not require such protection, as their insulation is generally considered sufficient to withstand normal wear and tear without additional means of protection. Thus, the focus on 4 AWG or larger wires is crucial for maintaining safety and reliability in electrical installations.