Help explain how this receptacle is wired?

Question

My house was built in 1955. Original cloth braided wiring. However, the words are visible on some of the wires in the attic and they do say that they have a ground wire. My ground outlet tester confirms that the outlets are grounded.

Today, I was looking at this outlet and it was wired differently than I have seen before (power was off at the breaker and I was positive it was off). I was given advice to not touch anything and have an electrician come out because I don't know what I'm doing. Which is fair, I don't know too much about this. But I'd like to learn for my own knowledge.

The wiring to the receptacle has two hot wires screwed in and one neutral wire screwed in. The other other neutral is put in the back "stab in." The ground screw at the bottom left of the receptacle does not have a ground wire around it. However, my ground tester said it was grounded correctly. If I look in the back of the box, I can see what appears to be a ground wire twisted together. However, I don't fully understand how it's grounded back there.

Here are a couple of pictures:

The hot wires

The one neutral wire

The stab in neutral in the back

What I think is the ground wire in the back

A few questions:

1. What have one neutral wire stab in? Why not just use the open screw that is there? As you can see it came loose in the picture. So the outlet isn't working.
2. Why isn't the ground wire around the ground screw? The way it looks currently is that the two ground wires are twisted together. Neither is connected to the ground screw terminal. My understanding is that they should be connected, preferably with a wire nut instead of just twisted together, and then one of the ground wires should go to the ground screw terminal. From what I can tell, that isn't being done and they are just twisted together in the back. How come I'm getting a reading that it is correctly grounded? Is it because the yoke is metal and both the yoke and copper are touching the metal box?

Any help would be greatly appreciated!

Answer 1

I was having a hard time making out where the neutral with the bad insulation came from. it did not look wrapped on the other screw or no wire left there I can see. That bothers me unless there was a back stab on the receptacle then the long strip would make sense it pulled out.

One common place for solid wire to break is at the strip point if the wire is nicked or not (the reason most electricians won’t use solid wire in industrial locations or where there is high vibration).

The grounding conductors in the box should be connected to the box and the box can be the ground to the receptacle.

To me it looks like the hot jumper between top and bottom receptacles is intact so there is probably another receptacle that was not working since this one was dead. But if the hot tab is broken one of the receptacles is probably switched.

Last the wrap on the neutral is the wrong direction, the hot conductors are correct.

Code specified wrap is 66-75% the code book shows this as aluminum wire but inspectors use that as a guide for copper also.

Answer 2

Backstab

A backstab, when working properly, is no different from a screw connection. Typically you will have a chain of receptacles where all except the last receptacle has a pair of cables - black to hot, white to neutral from one cable to top of the receptacle and black to hot, white to neutral from the other cable to the bottom of the receptacle. Each of those 4 wires could be screw terminal or backstab. Generally you will see all backstab (original install, fast work) or all screw terminals. But there is no electrical reason you can't have a mix.

However, as you have found out the hard way, a backstab wire can come out more easily than from a screw terminal and cause problems.

Remove it fully from the backstab and connect to the corresponding screw instead. You might have to trim the bare wire a little bit - it looks like (but hard to tell from the picture) the bare wire may be too long to fit in one wrap around the screw.

Grounding

While grounding is preferable done using a wire to a screw, it is often acceptable (as I understand it, more for switches than for receptacles) to ground from the metal yoke to a metal box using the grounding screws. That may not be as good a connection as a proper ground wire to a ground screw on the receptacle, but it would certainly be enough to show proper ground using a tester. Go ahead and ground it properly with a green or bare ground wire to the screw on the receptacle and the other ground wires.

Answer 3

Receptacles can be split in two. One socket can be always hot while the other socket can be switched on and off. So you can enter a room, hit the wall switch and turn a table lamp on and off.

To do convert a receptacle, you break a small conductor between the two sockets.

That's what it looks like to me.