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*TOTALLY* isolating phone from line, electrically?

Discussion in 'Electronic Basics' started by Don Bruder, Dec 10, 2003.

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  1. Mark

    Mark Guest

    Go to

    They specialize in lightening protection products and have them for
    telephone and datacom applications.
  2. Ken Taylor

    Ken Taylor Guest

    You could use a cell phone, albeit with possibly reduced throughput.

  3. w_tom

    w_tom Guest

    First, if incoming was a phone line, then what was the
    outgoing path? Without both incoming and outgoing paths, then
    no damage can happen. Second, how do you explain why a
    transient completely ignored that telco provided 'whole house'
    protector? Phone line typically has surge protection. AC
    electric typically does not.

    Did a transient enter on phone line, damage modem, then
    stop? Of course not. That would even violate primary school
    science lessons. Before damage occurred, first a complete
    circuit was conducting. Electricity flowed from cloud to
    earth via those modems. Only after the complete circuit
    conducts through everything in that circuit, only then did one
    part become damaged. Where that damage happened does not
    define the incoming path. It only defines what was in that
    destructive circuit.

    An AC electric transient that passes through modems
    typically damaged a modem's DAA section. It is, after all,
    where galvanic isolation causes highest energy dissipation.
    The DAA section is on phone line side of a modem; and often
    damaged by surges incoming on AC electric. This from one who
    repairs surge damaged modems (even back in the 1200 baud days)
    by first tracing a surge path, and then identifying all failed
    components. In fact, this modem was repaired after an AC
    mains surge damaged its DAA section.

    Damning evidence. I not only defined theoretically why
    modems are damaged by incoming transients, but also repair
    them at the component level - experience also cited.

    Again, until one can say why a telco provided surge
    protector did not earth the incoming transient, then one
    cannot claim modem was damaged by phone line. You can only
    speculate that an AC electric transient found earth ground via
    that phone line. Incoming modem destructive transient was
    from AC electric; outgoing to earth ground on phone line.

    Another's technical analysis to the same conclusion:

    Review your facts. Some IC pins on that serial port card
    make a direct connection to one AC mains wire. Use a
    multimeter to confirm it if you don't believe it. A direct
    connection that bypasses computer power supply. AC mains,
    through serial port card, through modem, to earth ground via
    phone line. Again, did the surge enter serial port card from
    modem, damage card, then stop? Of course not. Serial port
    card was in the same destructive circuit as modem. Follow the
    path of that surge from AC mains to earth ground via phone
    line. Because there is not 'whole house' protection on your
    AC mains, then AC mains is a perfect (and usual) path for
    surge damage - the complete electrical circuit. How many more
    reasons need I post? Another ten? These are damning facts
    base on fundamental principles and decades of personal
  4. w_tom

    w_tom Guest

    How does computer or telephone get electricity if it only
    connects to outside world using a fiber optic? Why recommend
    a high tech, expensive solution when effective protection
    methods are so effective, so less expensive, and proven in
    most every town every year for generations? The basic concept
    is called earthing - as Polyphaser application notes make
    woefully obvious.

    Early ham radio operators would suffer damage from
    lightning. They would even disconnect the antenna and place
    it inside a mason jar. They still suffered damage.
    Disconnecting alone did not stop damage. Distance alone (and
    that mason jar) was not sufficient. Then they earthed the
    antenna. Suddenly damage stopped happening. Of course. That
    is the principal behind well proven protection - without fiber

    Any wire that enters the building must first connect to
    central earth ground - as Polyphaser so repeatedly
    demonstrates. The important distance is the one to earth
    ground. Not farther; closer. Connection to central earth
    ground typically must be less than 10 feet. Some wires can be
    connected directly to earth ground (cable and satellite
    dish). Others must make that central earth ground connection
    via a surge protector.

    Nothing difficult about this. It's old, well proven
    technology. Protection is about earthing. Same principle that
    makes Franklin air terminals (lightning rods) so effective. A
    surge protector is only as effective as its earth ground.
  5. It might look that the telephone line get the lightning into house,
    but thigns are not as straighforward.
    What kills the device connected to the telephone line and the mains
    power is the huge voltage difference that happens between mains power
    and telephone line. This voltage difference can be cause by either:
    1. Lightning hitting the telpehone calbe, telephone central office
    where the cable goes or nearby the central office. This causes
    the telephone line potential to raise
    2. The lighting hits the electrical distirbution network. Your whole
    ground potential in your house raises to very many kilovolts
    This causes the voltage difference between the telephone wires
    that are grounded on the one end at the telephone central
    that is still the original ground potential (no raise there)
    It is the combination of mains connection and telephone connection
    that causes the msot disasters.
    The telephone modems are already isolated somewhat (1.5 - 4 kV osolation).
    This is not enough for ay real lighting protection.
    Ýou need a very high isolation to make the isolation work.
    There are some special products that convert telephone line to
    fiber and back, that could help in some this kind of cases.
    Quite expensive special solution.

    Usually the good enough protection can be made with proper
    whole house protection plan, where there are surge protectors
    for mains and telephone line, and both of those are connected
    togerher and wored to good ground connection. This kind of
    arrangement usually limits the voltage differences to something
    the equipment can handle.
    Here is one isolator:
    It promises up to 75,000 Volts isolation (4 inch air gap).

    Here are links to some other products:
    The existing products on the market I mentioned are from around
    370 USD and up.
  6. A normal PC definately needs the mains power connection
    or it needs to be a laptop running on batteries.

    If the device is very low power device (just uses
    milliwatts or tens of milliwatts), then it is possible
    to feed power to it optically through fiber optic cable.

    Ot use it off the solar panels from room lighting.
    Proper earthing combined with right surge protectors is
    a very good solution for this.
    You are right.
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