Q. Does the NEC require GFCI protection when replacing a non-GFCI receptacle in an existing building?
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A. When existing receptacles are replaced in locations where GFCI protection is currently required, the replacement receptacles must be GFCI protected [406.4(D)(3)].
Exception: Where receptacle replacement is impracticable, such as where the outlet box size won’t permit the installation of a GFCI receptacle, a GFCI‑protected grounding‑type receptacle marked “GFCI Protected” and “No Equipment Ground” is permitted.
The GFCI protection required by Sec. 406.4(D)(3) can be accomplished by a GFCI circuit breaker for the entire circuit or an upstream GFCI receptacle, but check other requirements in 406.4(D).