Outlets that seem to be on same circuit, but not behaving that way

Question

I'm trying to install a GFCI outlet in my kitchen. My understanding is that you can install one GFCI on the circuit and this will protect all of the other outlets. This is assuming that the GFCI outlet is installed at the beginning of the circuit. (Correct me if I'm wrong about this).

In attempting to identify the outlet at the start of the circuit, I went one by one and disconnected each one of them, testing the others as I did that. They all seem to operate independently of each other. Disconnecting one outlet did nothing to the others.

What makes this puzzling to me is they are all connected to the same circuit breaker. So wouldn't this mean they are all on the same circuit? If they are all on the same circuit, why do all of them continue to work no matter which one is disconnected?

Answer 1

The old way of running kitchen plugs was to split the top and bottom plugs so each plug was on a seperate feed. This was accomplished by running 3 wire between the plugs and removing the breaker tabs, the entire thing was conected to a dual pole break so the entire plug would trip at once.

If your house was built to code before the advent of gfci this is probably what is going on.

If you test the breakers for those plugs and find them tied together with breaker bars or some othe way this is almost certainly the case.

Unless they were wired with 12g cable you will need dual pole 15a gfci breakers rather than 20a gfci plugs to add gfci protection or to run new cable and 20a breakers.

Fyi: not an electrician

Answer 2

Depends how they are wired - "star" wiring (where each outlet has its own wire leading back to a junction box) will give the described result, but is unusual.

Then again, as implied in comments, a "pigtailed" circuit where each outlet is connected to a short wire that connects (typically with a wirenut in the box) to the wires leading to the source of power or previous outlet on one side - the next outlet on the other will be unaffected by disconnecting the receptacle from the short wire.

Being aware of the possibility that the current outlets are split via a Multi Wire Branch Circuit (MWBC) as @beast describes is wise, as this was a very common way to get the required two kitchen circuits (20 A these days, not sure if it was always 20A when it started to be required.) Look for the tabs being broken between the hots sides, and (usually but not always) red, black and white wires being connected to the outlets.