For a while now, I've had a switched receptacle where only one of the outlets worked, so I dropped by the hardware store to pick up a replacement.

The first thing I did was measure the voltage at the receptacle. With the switch off, the upper receptacle measured 121V. The bottom receptacle measured 28V. WTF? With the switch on, it measured 121V in both receptacles.

At this point, it seemed that the formerly bad outlet was now working. Later on, it appeared that there was an intermittent connection in a wire nut, which I fixed. So, technically, I solved my problem, but I'm really concerned about 30V running through that outlet.

Anyway, here's how it's wired: The receptacle was evidently intended to be wired with one outlet switched, the other always on. The always-on outlet was the one not working at all. There are two cables coming into the box: one 2-conductor plus ground (B, W, G), and one 3-conductor plus ground (B, W, R, G). The Gs are all tied together and then connected to the ground screw on the outlet. Each W is tied to a neutral screw on the receptacle. The B from the 3-conductor cable is tied to the switched outlet's hot screw. The R from the 3-conductor cable and the B from the 2-conductor cable are tied together, and from there go to the hot for the always-on outlet.

At the switch panel, there is the outlet's switch, plus a switch that controls the porch light. In that box, there are four cables, three 2-conductor cables (let's call them A, B, and C) and one 3-conductor cable (D). The grounds are all tied together and attached to both switches. The whites are also all tied together. AB goes to the bottom of the porch switch. BB, CB, and DR are tied together and then go into the bottom of the outlet switch and the top of the porch switch. DB goes into the top of the outlet switch. This seems completely screwed up to me.

I'm not sure what is connected to what, though it seems that the 3-conductor cable is the same one in both locations.

Does anyone have any ideas what's going on? I'm starting to suspect a bad switch.

I'm going to see if I can post a wiring diagram in a bit, since the textual explanation is a bit hard to visualize.

Edit: changed to reflect common terminology