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Thread: Did BT get it wrong?

  1. #1
    Automated Home Lurker
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    Default Did BT get it wrong?

    Hi,

    As a result of phone noise problems occurring after I installed ADSL, I checked out every extension/connection in my house very carefully. Nothing untoward found, correct cables used etc.

    However, I did find that there was -52.5V (to earth) on terminal 5 of my (old style) BT NTE5 Socket and -4.2V (to earth) on terminal 2 - i.e. on the opposite terminals to that shown on publically available wiring diagrams. The BT installed wire colours appear to be correct however - i.e. orange to 2 and white to 5.

    This suggests that somewhere along the line between my house and the exchenge the wires have been crossed. Did BT get it wrong at the exchange or at the pole (and could this contribute to my noise problems) or doesn't it matter which line has the -50V?

    Thanks in advance.

  2. #2
    Automated Home Lurker
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    Default Re: Did BT get it wrong?

    Polarity is not an issue, and BT can provide it either way around.

    It should be noted that the numbering on the IDC connectors is a mirror image of the pin numbering.

    Full information in the BT spec
    http://www.sinet.bt.com/351v4p5.pdf

    Paul

  3. #3

    Default Re: Did BT get it wrong?

    Quote Originally Posted by robert_beasley

    This suggests that somewhere along the line between my house and the exchenge the wires have been crossed. Did BT get it wrong at the exchange or at the pole (and could this contribute to my noise problems) or doesn't it matter which line has the -50V?
    Hi Robert,

    Its highly likely that the wires are crossed but as far as the incoming line is concerned, for a normal exchange line, it doesnt matter which way round the two wires are.

    It DOES matter for some types of PBX which use "Earth Calling" (or "Ground Start" as the US prefer to call it). Any PBX use in the home wouldnt care either.

    The only time a reversal will cause you problems is if you reverse the A & B wires BETWEEN SOCKETS.

    Hope that helps

    Keith
    KAT5.tv - affordable high quality AV Distribution
    http://www.kat5.tv

  4. #4
    Moderator toscal's Avatar
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    Default Re: Did BT get it wrong?

    Have you connected the in line filters to your phones. I had a similar problem with my fax machine. So like you checked the wiring etc.Only to find I had forgotten to connect the filter between the socket and the fax machine. Once the filter was connected the noise dissapeared.
    The filters normally come with the ADSL modem fromyour provider. But if not Maplin sells them product code is A72AG. They are a bit expensive at 6.99 pounds and I'm sure if you do a Google you can find a cheaper source.

  5. #5
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    Default Re: Did BT get it wrong?

    Thanks very much for your help guys. You have put my mind at rest on this one.

    I think that the noise problem was in fact caused by the error I made many years ago in installing a 35m extension from the main incoming socket to my office. I ran the cablemainly in a shielded underground duct under my lawn. This was before the advent of ADSL and I used common flat extension cable. To make nmatters worse, it ran alongside the main power cable to the office.

    Having researched this forum and taken other advice, I replaced the cable yesterday (what a job) with exterrnal grade 4pair Cat5e (rather than BT's CW1128 spec which is said not to have enough twists/inch to be of much use in this situation) and so far, the noise seems to have gone away. My ADSL speed has at least doubled - which is a bonus.

    So, touch wood, the problem has been solved and the possibilty of a miswire by BT not now an issue.

    Thanks again.

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