O NEC simplesmente informa "onde é fornecido através de um interruptor de circuito de falha de aterramento" neste caso, assim você pode conseguir isso por um receptáculo GFI, um dispositivo GFI sem máscara ou um disjuntor GFI.
Você não pode, no entanto, usar um disjuntor AFCI, a menos que seja um dos novos (e raros) disjuntores AFCI / GFCI. Boa sorte em encontrar um. Eu acho uma Siemens na Amazon e é sobre isso.
Veja "(c)" abaixo.
Do NEC 2011:
406.4 General Installation Requirements
Receptacle outlets shall be located in branch circuits in accordance with Part III of Article 210. General installation requirements shall be in accordance with 406.4(A) through (F).
(D) Replacements.
Replacement of receptacles shall comply with 406.4(D)(1) through (D)(6), as applicable.
(2) Non–Grounding-Type Receptacles.
Where attachment to an equipment grounding conductor does not exist in the receptacle enclosure, the installation shall comply with (D)(2)(a), (D)(2)(b), or (D)(2)(c).
(a) A non–grounding-type receptacle(s) shall be permitted to be replaced with another non–grounding-type receptacle(s).
(b) A non–grounding-type receptacle(s) shall be permitted to be replaced with a ground-fault circuit interrupter-type of receptacle(s). These receptacles shall be marked “No Equipment Ground.” An equipment grounding conductor shall not be connected from the ground-fault circuit-interrupter-type receptacle to any outlet supplied from the ground-fault circuit-interrupter receptacle.
(c) A non–grounding-type receptacle(s) shall be permitted to be replaced with a grounding-type receptacle(s) where supplied through a ground-fault circuit interrupter. Grounding-type receptacles supplied through the ground-fault circuit interrupter shall be marked “GFCI Protected” and “No Equipment Ground.” An equipment grounding conductor shall not be connected between the grounding-type receptacles.