Q. When is an insulating bushing required on raceway fittings?
A. Where raceways containing conductors 4 AWG and larger enter an enclosure, the conductors must be protected from abrasion during and after installation by a fitting that provides a smooth, rounded insulating surface, such as an insulating bushing [300.4(F)].
Rigid nonmetallic conduit male-adapter termination fittings are sometimes considered to provide the required smooth rounded insulating surface. But check with the authority having jurisdiction (352.46).
One last thing: insulating bushings aren’t required where a raceway terminates in a threaded raceway entry that provides a smooth, rounded, or flared surface for the conductors. An example would be a meter hub fitting or a Meyer’s hub-type fitting [300.4(F) Ex.].
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