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  1. #1
    Platinum Lounger
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    N.Amer phone wiring

    Non-urgent; just curious.

    What signals are carried by each wire?
    I have moved into a 3-bedroom apartment and am replacing every wall socket/cover plate, lights, power, phone.
    I keep coming across Yet Another Phone Socket where the previous tenant applied latex paint In The Hole. I rip off the painted-over socket and install a brand new telephone jack-and-plate ($2.99 at your local hardware store.)
    I can comprehend the instructions ("connect red to red, green to green, yellow to yellow and black to black"), but have now come across some jacks where only the red and green were connected.
    (1) What purpose is served by the yellow and black?
    (2) Why would some of the (seven so far) sockets have all four wires connected, and some only two?
    I suspect that these are the wirings for the building when it was built about 40 years ago.

  2. #2
    Plutonium Lounger Leif's Avatar
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    Re: N.Amer phone wiring

    Perhaps somebody added room-to-room audio because they didn't have any unused communal TV antennae outlets?
    <img src=/S/grin.gif border=0 alt=grin width=15 height=15>

    If it is anything like UK wiring, the telephone signal itself comes in on two cores. Extensions will have one or two additional cores connected which detect when a handset is off-hook, and mute the bell/ringer on the other 'phones. This was necessary in the days of pulse dialing - I'm not so sure it is now.

    You may find more info here...

  3. #3
    Plutonium Lounger
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    Re: N.Amer phone wiring

    The read and green wires are the "primary" phone line. The yellow and black were intended for a second phone line, but traditionally remained unused until the advent of (A)DSL; this uses the spare lines to transmit the internet signal.
    In places built before (A)DSL became popular, technicians sometimes didn't bother connecting the yellow and black wires since they weren't used anyway.

  4. #4
    Platinum Lounger
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    Re: N.Amer phone wiring

    >The yellow and black were intended for a second phone line, but traditionally remained unused until the advent of (A)DSL;
    You got me all excited there, for a minute!
    It sounded to me that by connecting only the red/green I'd skip the DSL signal.
    To test this I took a phone and plugged it without the DSL filter into the socket I wired this morning, which had only a red/green.
    sadly, the hiss is still there.
    I had hopes that Bell had hooked the DSL to yellow/black leaving the red/green for voice. Alas, no.

    I suppose that Bell, in its infinite wisdom, decides that a 40-year old building may have only red/green connected, and so pipes the DSL down that pair.

  5. #5
    Platinum Lounger
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    Re: N.Amer phone wiring

    > You may find more info here...
    Thanks, I did, but it left me confused, since it doesn't describe red/green and yellow/black.
    Perhaps Toronto, self-styled World-Class City, chose to ignore standards.

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