I just moved in to a new home I'm renting to find this, near where a TV would usually be installed.

This is near TV height, under a TV mount that was installed by the homeowners. top And this is on the bottom near the baseboards. bottom

When we arrived, the white power cable was plugged in to both ends.

I took off the faceplates, and it seems that BOTH outlets are wired to the mains, but I can't get power from the one on the top, and I don't have a multimeter with which to test them.

If I wanted to use them correctly, how would I?

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    This is way off the reservation. Even setting aside @Tester101 's comment about it being not up to code, I have no idea what it's supposed to do. – Hank Feb 26 '15 at 0:09
  • Your pictures are a little blurry and parts of your description are a little vague. Can you please confirm. On the top you have a single power outlet and to the left is an opening to run cables. On the bottom you have an opening to run cables and the blue area has coax and network connections? You also mentioned power and the cord was plugged in at both ends. The blue area isn't big enough to have coax, network and power so please elaborate where the other end of the extension cord was plugged into and where everything is in more detail. – OrganicLawnDIY Feb 26 '15 at 1:05
  • If the female/male plug ends are different ends of the same cord, this could be used to plug into a switched outlet on a cable box or some such to power off something below the TV when the box is shut off. Only thing I can think of to cover this. – Pᴀᴜʟsᴛᴇʀ2 Feb 26 '15 at 1:38
  • @OrganicLawnDIY Sorry, the "blue area" on the bottom is the male 110 receptacle. The coax and network are off to the left. I was just trying to say that it's near the baseboard (That's probably a better way to say it). The extension cord was plugged into the female 110 at the top, and the male 110 at the bottom. – Jonah H. Feb 26 '15 at 1:38

I've seen installations like this before, and I think you're missing a piece of the puzzle.

First step, is to get that cord out of the wall.

In a typical instsllation, the male receptacle at the bottom of the wall is connected to the upper receptacle via NM cable (or other approved wiring method). The male end of a cord (like the one in the wall in your case) plugs into a nearby receptacle, while the female end plugs into the male receptacle (like the one in your photo). This cord passes power to the upper receptacle, via the NM cable within the wall.

I'm not sure if this is how your setup is wired, since you say the receptacles are connected to the mains. But this is how a typical Installation works.

You should be able to verify this with a multimeter (when you have access to one). With nothing connected, neither of the receptacles should have power. You should also be able to get continuity between the receptacles.

Plugging the cord in as described above, should supply power to the upper receptacle.

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  • Next time I'm near a computer, I'll draw a diagram to hopefully be more clear. – Tester101 Feb 26 '15 at 2:14
  • Ah. That makes sense why someone would have a male receptacle there. Never seen that before. Didn't even think that it would be acceptable to have an isolated circuit powered by extension cord. I thought I read it as there was power on the bottom though so I'm confused. – OrganicLawnDIY Feb 26 '15 at 2:19
  • @OrganicLawnDIY I'm not sure what I said is correct in this case, I'm just explaining how I've seen things like this done. I was concerned when he said both receptacles are connected to mains, but I guess he could have mistaken the cable connecting the two receptacles as a connection to mains. – Tester101 Feb 26 '15 at 2:22
  • Do you happen to know if the setup you described is code compliant according to NEC? – OrganicLawnDIY Feb 26 '15 at 2:27
  • @OrganicLawnDIY I'm pretty sure it is, as long as all the devices used are listed for the use, and proper cable is used inside the wall. – Tester101 Feb 26 '15 at 2:29

If I wanted to use them correctly, how would I?

I'm still confused about the details but this part I can answer.

These types of wall plates are used to hide the wiring for wall mounted TVs. You have an outlet behind the TV so that you don't have a power plug running down the wall and you have an opening that allows access to the stud cavity behind so you can run low voltage wires (HDMI, coaxial for cable or antenna, network, digital audio, speakers, etc) behind the wall down to the corresponding outlet in the lower mounted faceplate.

Next to the opening on the lower faceplace can be a number of different fixtures. Either an electrical outlet or video, data or voice jacks.

The outlet would be for things like DVR players that may be on a shelf or small cabinet.

The cable pass through holes are not intended to be used for mains power and as Tester has indicated it is not wise to use it for that.

I can't tell from your picture if the bottom receptacle is a combination coax/network or a male 110 receptacle.

If it's a male 110 receptacle that doesn't make any sense why it would be connected via extension cord to the other outlet. The only thing I can think of is that the both outlets are supposed to be on the same circuit but somehow the connection between the two was broken which may have resulted in other fixtures further down the circuit not operating. That's just a guess but the only reason I can think of why it would be like that.

There's no reason to have a male 110 near entertainment equipment. My advice would be to get an electrician to sort things out because when people do strange things like that it's frequently a temporary fix for a more serious problem.

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  • See my comment on the question to clear up some things you found confusing. – Jonah H. Feb 26 '15 at 1:39
  • @Crazydog Thanks for the clarification. You said the top outlet has no power. When you removed the extension cord did you notice any other lights, outlets or other devices lose power as well? There's no common use case for a 110 male outlet in that location so my answer is unchanged you need to get the male changed to a female and resolve the problem with the top outlet not working. Ditch the in wall extension cord and run your A/V cables through there instead. – OrganicLawnDIY Feb 26 '15 at 1:51
  • Nope. Nothing changed. I wont be using the outlet, as I'm going to have a projector screen where a TV would normally go. Do you think it's safe to just leave the extension cord plugged in to both the male and female outlets and ignore it, or should I definitely replace the bottom faceplate and outlet? – Jonah H. Feb 26 '15 at 2:57

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