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I stumbled across this device while renovating the bedroom of my house. It is screwed into the wall. There is only one wire going into it. The wire has several small diameter wires inside the sheathing and those wires are connected to the device in some nontrivial fashion.

Is it something abandoned?

electrical device

22

It's a beat up telephone jack. You can see the actual plastic jack off on the left, and there was originally a cover over the box.

  • Either someone was in there recently, or that spot is never vacuumed. The screws and washers are lying on the ground beneath it. The cover would contain a modular jack or an old school 4-prong, and possibly a DSL filter. – Harper - Reinstate Monica Jun 11 '17 at 15:47
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    @Harper, People rarely vacuum underneath the carpet. The hardware pieces you describe are sitting on the tack-strip used to secure the carpet. – Makyen Jun 11 '17 at 16:17
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    I'd check whether there's voltage on the thing. If found, trace the wire back to a place where it's safely clippable. People didn't always disconnect when they stopped using these things. It might have 48 volts DC across it: jkaudio.com/article_10.htm – Wayfaring Stranger Jun 11 '17 at 16:35
  • They were under the carpet? That's bizarre, normally one takes those screws off when connecting wires and puts them right back. That suggests they did it during construction and their purpose was to permanently abandon the junction (and therefore the cables to it). – Harper - Reinstate Monica Jun 11 '17 at 17:05
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    As this is a phone connection, power isn't supplied therough your normal breakers -- it comes from the phone company. It's weak but still enough to give you a jolt (especially if it rings while you're touching it with sweaty hands). – Chris H Jun 12 '17 at 9:24
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It's a four-wire junction box (missing plastic cover) for connecting a phone or other customer premises equipment to one or more central office lines. It predates the use of phone jacks.

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    Actually it would be likely for something just like that to be under the phone jack. – Harper - Reinstate Monica Jun 11 '17 at 17:07
  • Concur. I've wired many of them. Haven't seen one in years now, though. – SDsolar Jun 11 '17 at 17:29
  • @Harper - I disagree. The 4-prong jack was a later development, and often you would see units such as the above retrofit with one, but if that were the case it would still be there. The cover was removed and the screws unscrewed to release the phone set's cord when it was being removed. – Hot Licks Jun 11 '17 at 19:55
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Other answers provide great info, just adding a picture for reference. At first glance I thought it was an RJ45 block, but this has less screws.

Four Conductor Surface Jack

Image from https://www.commgear.com/allen-tel-4-cond-surface-jack-biscuit.html

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