Adding GFCI Outlet in 2-wire ungrounded branch

Question

I have a 1938 house. Most of it has had the wiring upgraded. However, I have one room with multiple outlets that are all ungrounded with the original cloth covered wiring. There is only one pair of wires (1 black, 1 white) coming out of each outlet on the circuit. I want to add a single GFCI outlet to the first receptacle in the circuit to provide ground fault protection to it and all the other outlets downstream. But can I do this by simply connecting the single pair of wires in the first outlet to the the GFCI Line connectors? I don't see how this would work to break the circuit downstream if there there aren't two pairs of wires available (a pair of Load and a pair of Line wires) to hook up to the GFCI outlet. I really don't want to mess with or modify any of the the old wiring.

If it isn't possible to protect the entire branch with a single GFCI outlet, would I just be better off installing a GFCI breaker that serves that branch?

Answer 1

Broadly, fix this at the other end, unless you can find the point where it all ties together - which can be, but need not be a breaker. If you can find the circuit somewhere that it's just one cable from the supply at the breaker, you can put in a box, or a couple of boxes, with a GFCI "deadfront" device and an AFCI "deadfront" device to protect the circuit, usually for considerably less cost than a GFCI/AFCI breaker.

With cloth covered insulation, I would definitely want Arc Fault as well as Ground Fault protection on this circuit. If the cable to the breaker box has been upgraded, you can do this in the "newer" cable. If not, you can cut out a section of the cloth-insulated cable long enough to reach the new box, and use new cable from the breaker to that point, connecting the old cable to the load terminals of whichever device you put second in line, if you choose to use both AFCI and GFCI as suggested.

Answer 2

You are correct that a GFCI outlet will only protect devices connected to its LOAD terminals (other than itself, of course). A GFCI breaker is definitely the next best thing (maybe even better, especially if you combine it with AFCI), but there is a possibility that that won't work either. In knob-and-tube wiring, two circuits will often share a neutral run. This should be visible in your main panel as a two-pole breaker with (usually) a black and a red wire connected to the two terminals. But if the circuit in question is part of a two-pole breaker where the two wires end up in the same cable (most likely 14/3, but possibly 12/3), it's possible that NM cable has been spliced to a knob-and-tube system with a shared neutral. In that case, a GFCI breaker won't work, because it relies on checking for a difference in current between the hot and neutral conductors. If the neutral is shared with another circuit, it will thus trip any time the other circuit is energized.