7900 Butt-In II
Lineman's Test Set
Ordering: 800-462-5532

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  • Rugged High-Impact Case
  • Monitor and Talk Switch
  • Extended Range Switch
  • Water-Resistant
  • Changeable Cords
  • Overvoltage Protection
  • Tone and Pulse Dial

  • Hardware » Outside Plant » 7900 Butt-In II

    The CMC 7900 BUTT-IN II has a case constructed of a high-impact plastic and the internal electronics are packaged for the rugged treatment it receives in the field.

    The keypad is constructed of a water-repellent rubber and the case is designed with tight-fitting joints to prevent moisture intrusion.

    The BUTT-IN II provides either DTMF or Dial Pulse output. The Pulsing Mode is selected by a Mode Switch (Tone/Pulse). A Talk/Monitor switch permits an off-hook condition for dialing and talking or a line monitoring function for monitoring the line without disrupting conversation, data or signaling.

    Two colored (red and green) Light Emitting Diodes (LED's) and a push-button switch (Polarity) provide a quick visual check of the circuit polarity.

    A Mute Switch allows the caller to shut off the transmitter for improved hearing from noisy locations. The last number dialed can be redialed by simply pushing a button on the keypad.

    An extended range switch allows the caller to extend the range of the test set when testing exceptionally long lines.

    An optional Ringer provides an audible ringing tone when the BUTT-IN II is in the Monitor mode.

    The CMC 7900A BUTT-IN II is provided with a five foot cord with insulating piercing alligator clips. The CMC 7900B is equipped with a one-foot cord and 346A plug to allow cord changes, and the 7900C is equipped with insulation piercing (spike and cluster of needles) alligator clips.

    CMC's sturdy belt hook is easily replaced without disassembly and clips around a 7/16" strand.

    Technical Specifications

    Mode Selection Switch
    Talk/Monitor Switch
    Polarity Indication Button
    Mute Button
    Extended Range Switch
    Redial Button


    2000 ohms at 48 Vdc (20 mA minimum loop current)


    150 ohms typical


    120K ohm minimum at 1000 Hz


    Pulsing Rate - 10 pps 5%
    Percent Break - 60% 2%
    Interdigit Interval - 800 ms typical


    Tone Frequency Error - 1.5% maximum
    Level Per Tone Pair +2dBm max, -6dBm min
    Low vs. High Tone Difference - 4dBm max


    Size 10in x 4in x 3in
    Weight 1.25 pounds (567g)

    * Specifications are subject to change without notice.

    Ordering Information
    Part Number


    CMC 7900AButt-In II equipped with 5-foot cord with insulation piercing (spike) alligator clips
    CMC 7900BButt-In II equipped with 1-foot cord terminated with a 346A plug to allow cord changes
    CMC 7900CButt-In II equipped with a 5-foot cord with insulation piercing (spike and cluster of needles) alligator clips
    OPTIONAL RINGER - An "R" suffix at the end of the number will indicate that a "RINGER" is included (i.e., 7900AR, 7900BR, 7900CR)
    OPTIONAL CORDS - These cords used with the CMC 7900B Butt-In II are terminated by a 471A female connector
    CMC 0040Cord equipped with standard insulated alligator clips for central office use
    CMC 0042Cord equipped with a 310 plug
    To order the 7900 Butt-In II and its accessories, contact the CMC Customer Service group by telephone at 800-462-5532.

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    CMC Communications Manufacturing Company
    2234 Colby Avenue, Los Angeles, California 90064
    530 Gordon Baker Rd., Willowdale, Ontario M2H 3B4 CANADA

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