Another (US) electrical wiring problem.

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

My mind is having trouble reading your posting, because what you actually have are more commonly known as a two-conductor (plus ground) and a three-conductor (plus ground).

Arghh.. it's taking me forever to parse your posting and make that correction in my mind..

Okay, I don't know about the 30V (but that's very bad).

However, for your first (outlet) box:

The 2-wire cable is delivering electricity from the panel. The bare ground wire should be directly bonded to the metal box, and go from there to a pigtail with the bare ground wire from the other cable. Black is hot, White is neutral. All is good.

The 3-wire cable goes from there to the switch. For some odd reason, they chose the red wire to continue the hot run, rather than black. White is still neutral. The Black wire acts as a hot return from the switch to the switched outlet.

At the switch box, the 3-wire cable (above) is delivering electricity from the panel on the Red wire, via the outlet box discussed above.

From here, one 2-wire cable goes to the porch light -- the black for this is connected to the incoming Red (hot) wire. Okay.

The other two 2-wire cables continue the circuit onwards to additional outlets elsewhere.

All perfectly normal, except I would have swapped the red and black conductors (at both ends) for the 3-wire cable. No biggie, the code usually allows either method.

EDIT: As elperepat pointed out, the circuit could be the other way around, with the outlet box being downstream from the porch switch, and not the other way around. This doesn't really affect anything, though, other than which bare ground wire gets hooked directly to the screw on each metal box.

-ml

Mmm.. I suppose the 30V at the not-so-off outlet could be caused by induction, since the switched black wire runs alongside the hot red wire for (how far?) a decent length. Mmm.. I oughta be able to measure that somewhere here just to see if induction is a real possibility or not with this.

-ml

[edit](mlord wrote his replies while I was writing this)[/edit]

Main power comes from either BB or CB.

Red is always live. It brings power from the switch box to the outlet box, then goes somewhere else.

Black is switched. It is powered by the switch. The fact that line is on the bottom of the switch is not usual, but it should work.


The 30V you're seeing may be caused by induction (the two wires parallel are long enough to act as primary/secondary of a transformer). Try plugging something (night light, lamp) in the switched receptacle and just pull it back enough to measure voltage across prongs. If it's induction, voltage should drop to 0V. It should not cause problem.

A drawing would probably help though.

Okay, so you think it's all wired properly. Fair enough. Seems kinda weird to me. Maybe I was initially thinking that there would be two hot cables coming into the switch box, and tying all those neutrals together seemed odd. But I guess that's probably not the case.

The distance from the switch to the outlet is about 15 feet. There's currently nothing plugged into the outlet, so there shouldn't be any, uh, flux(?), to cause induction, right? I mean, effectively, it's all open circuits.

I think I'm going to remove the outlet switch and test its resistances.

Quote:
My mind is having trouble reading your posting, because what you actually have are more commonly known as a two-conductor (plus ground) and a three-conductor (plus ground).

The reason for this, by the way, is that electical codes seldom consider the bare ground wires as "conductors". They're just present for safety, and under normal circumstances don't conduct anything. And they usually don't count for "box fill", whereas real insulated conductors do count for "box fill".

The term "box fill" refers to electrical code limits on how many conductors are allowed to enter/exit a given-size electrical box, based on the shape and cubic-inch volume of the box. The bigger the box, the higher the "box fill" limit.

A typical deep wall outlet box has a fill count maximum of 6, which allows for a circuit to enter on 2-wires (plus bare ground), exit on another 2-wire cable, and have a third 2-wire cable venture off to a switch and back again. Total of 6 "conductors" in the box, plus the three bare ground wires.

Fill count gets more complicated than that, as it also can take into account how many plastic wire connectors are present, plus other details. EDIT: I actually fibbed above: the box fill for that example was really 8, because two plastic wire connectors are needed to hook it all together.

Cheers