Which AWG size is indicated for requiring an insulating bushing when entering a box or conduit?

The requirement for an insulating bushing is addressed in the National Electrical Code (NEC), specifically within the guidelines concerning the protection of conductors as they enter boxes or conduits. Insulating bushings are intended to prevent damage to the conductors, particularly at the points where they are subject to mechanical stress or potential abrasion.

In this context, the correct answer points to 4 AWG as the size at which conductors generally require such protection. When conductors of this gauge or larger are pulled into a conduit or connected to a box, the use of insulating bushings becomes crucial to safeguard the insulation from being compromised.

Conductors that are smaller in gauge, such as 6 AWG or 8 AWG, do not necessitate the same level of protection under the NEC guidelines, as they are deemed to have less potential for causing damage due to mechanical stress. Therefore, the 4 AWG size specifically aligns with code requirements for insulating bushings at critical entry points, ensuring both safety and compliance within electrical installations.