Throughout Chapter 3 of the NEC, a Fine Print Note calls attention to 300.4(G) Insulated Fittings. This rule requires the use of insulated fittings when raceways containing ungrounded conductors 4 AWG or larger enter a cabinet, box enclosure, or raceway. A substantial fitting providing a smoothly rounded insulating surface usually provides the protection for the conductors, unless the conductors are separated from the fitting or raceway by substantial insulating material that is securely fastened in place. Conduit bushings constructed wholly of insulating material can't be used to secure a fitting or raceway. The insulating fitting or material must have a temperature rating not less than the insulation temperature rating of the installed conductors. This cabinet violates that rule because the fitting at the bottom right is metal.

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