This mystery thing is mounted to a ceiling joist in the basement of a 1940s house. I have a couple of questions:

  1. What is it?
  2. Is there any reason I couldn't rip it out and run new Cat 5e's from the NID to the wall jacks, just for the sake of modernizing? (Is that how they are supposed to get wired up?)

enter image description here

  • 8
    Just older type of junction box for telephone connections. Newer types be made out plastic, but do same job. It could be clean up and or replaced, but make work for getting same use. If not broken, why fix.
    – crip659
    Feb 18, 2022 at 0:37
  • See diy.stackexchange.com/q/144387/18078 for a complete one
    – Ecnerwal
    Feb 18, 2022 at 0:51
  • 5
    Those old phone wires are likely full of staples so you'll have a hard time using them to pull Cat5 and they likely don't go where you'd want them to anyways. There's really no such thing as "modernizing" a land-line phone system. You'll just get an outdated system with new wires. Just cut it out and throw it away or leave it be.
    – gnicko
    Feb 18, 2022 at 1:58
  • 4
    @gnicko That's only true when you only use POTS for voice. Many people nowadays need a landline exclusively for DSL data, and there the quality of the wiring can make a big difference in attenuation and noise level, thus significantly impacting the attainable data rates (especially when you want to go to >100 Mbps).
    – TooTea
    Feb 18, 2022 at 10:35
  • 1
    If it's really that easy to just rip out and replace original telephone wiring with modern data wire throughout your 1940s house, I am jealous! I've been trying to figure out how to run data in my 1930s house without making massive holes in drywall and original plaster and it's largely impractical. :)
    – 640KB
    Feb 18, 2022 at 13:46

2 Answers 2


Standard Bell System (Western Electric, usually) terminal block. Appears to be missing the protective devices, but those are not needed since it's no longer the NID.

Sure, take it out and modernize if that makes you happier. Depending where the old wires run, it may not be at all easy to replace them, and there's no benefit to replacing them - what's there is standard and works fine for Plain Old Telephone Service - POTS or "analog lines" as they are known.

Here's an image of "what that used to do" when it was the NID/Demarc back in the day from a "Classic Rotary Phones" website. Note that in modern use it's just red and green unless you have two lines - the "yellow as ground" thing is very old - in the past multiple decades it would be another line on black and yellow, which would have run to another of those blocks "in that day."

enter image description here

If you really get bothered by the "messy" nature of it you can replace it with a newer terminal block while keeping the existing wires. But if voice quality on the lines is good as is, there's still no concrete benefit beyond "looks neater." Those were well made, and provide a very solid connection if wired properly.

  • 5
    Just because it's old doesn't mean it's bad.
    – FreeMan
    Feb 18, 2022 at 12:46
  • You should perhaps explain that the cable with all the stripped wires (the four-pair cable) runs to a box on the outside of the house. You can also explain that this outdoor box is not the new demarcation point between the wiring which belongs to the telephone company and the wiring which belongs to the customer. The protection devices were removed by the installer of the new box. There is a technical term for the box, but I can't remember it.
    – David42
    Feb 18, 2022 at 12:54
  • As both the questioner and I know, it's the NID - Network Interface Device (and Demarc) and it would be incorrect to say that "the 4-pair cable" runs there, as there at least 3 4-pair cables in the questioner's picture, at least one of which has not had the unused pairs properly dressed, (wrapped neatly back around the cable jacket out of the way) which creates a lot of the mess.
    – Ecnerwal
    Feb 18, 2022 at 13:32
  • @FreeMan True, but it is ugly!
    – Mohair
    Feb 18, 2022 at 18:11
  • 1
    @rrauenza the pairs in the questioners picture are already twisted. Yes, that includes the red/green yellow/black 2-pair cables. They are not twisted as tightly as cables trying to carry 100 MHz, but then, they are not trying to carry 100 MHz.
    – Ecnerwal
    Feb 19, 2022 at 0:29

That is a second generation Bell System lightning suppressor being used as a junction block. The missing threaded devices were carbon wafer lightning suppressors, known to fail "short" and induce a lot of hum on the telephone audio. There was also a gas fired screwed in suppressor (expensive white ceramic cartridges) used on priority data circuits and two-way radio remote transmitters. Normally, the bakelite termination units were on the outside of the structures where the over head lines met the inside wiring and protected from the weather by a snap-on rubber cover. Their predecessors were a pair of long fusible wires that were useless stopping direct lightning strikes that could explode a 500 series telephone. First balanced pair is Red-Green, Second Pair is Yellow-Black. Do not mix the wire pairing as the quad is balanced and prevents cross talk.

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