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Telephony in Australia - questions re circuits of 600 series connectors

Discussion in 'General Electronics Discussion' started by Cutty Shark, Nov 11, 2018.

  1. Cutty Shark

    Cutty Shark

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    Nov 11, 2018
    Hi all,
    I'll kick off my registered usage here by proposing the following questions:

    1) As far as I can discern from info out there, the ordered terminal assignments for a standard legacy 610 cream telephone socket for Australian "standard" domestic colours are as follows: Term. 1 - Term. 6 red, white, unused, unused, black, blue. The corresponding US Bell colours (some cables also found in Australia) are black, green, unused, unused, yellow, red. Several sources on the net agree with this, including a comprehensive Wikipedia article, which in this case seems authoritative. However in practice I have found some more recently manufactured cables differ in this colour order, such as (a) legacy black, white, unused, unused, red, blue - where the red and black wires are swapped.on the socket side. Or (b) on the plug side with Bell colours: black, red, unused, unused, yellow, green, where the green and red wires are swapped. I would like to know if these are wiring errors or serve a specific purpose. I don't think this has anything to do with straight through versus crossover cables, since only one of each pair is swapped in each case.

    2) The 'relative' positive potential (although it's actually only about 0.2V DC relative to earth) from the exchange is found these days on the blue wire (Term. 6) and the negative potential of -54V on the white wire (Term. 2). This surprised me, as I expected Term.1 and Term 2 to both be Tip (positive) voltages and Term. 5 and 6 Ring (negative) voltages, and I thought this was the historical reality (all Tip voltages are relatively positive). In the anomalous version of (a) above, the blue wire is labelled as Ring in an article where I found this configuration, even though it's relatively positive! I can see some issues with having two terminals on the same plastic prong 'opposite' in charge. For example, if one sets up a Mode 3 domestic circuit, say in back the 70's with a Fax upstream from the phone on a 611 socket, then if one unplugged the Fax to service it, the 611 socket terminals 1&2 would contact each other and reverse the direction of the downstream current to the phones (from its normal sense if independently hooked up to a separate exchange line. Since phones may not be polarity sensitive, this may not matter, but it's just a matter of unnecessary disorder in a phone circuit.
     
  2. kellys_eye

    kellys_eye

    4,284
    1,145
    Jun 25, 2010
    Purposely I suggest. I have used (home/business) telephone exchanges where the exchange-connected phones used the 'crossed' wires whereas other phones not on the exchange used 'uncrossed'. Made for some confusion when trying to use the domestic phones on the exchange.

    That said, the exchange phones could be either 'standard' types or intelligent types (with digital readouts etc) so you can understand why they change the wiring sequence.

    POTS phones are not polarity sensitive - they have AC ringing voltages and DC (capacitor) coupled audio circuits so it's not an issue.

    Designing systems that have less chance of errors during installation was the key to the original system. In other words not polarity sensitive.
     
  3. Cutty Shark

    Cutty Shark

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    Nov 11, 2018
    Thank you for replying. There does seem to be a certain level of ambiguity in domestic 'interpretation' of wiring rules, and a whole range of technology development spans the 40-50 year period in which the legacy cabling system was in place domestically in this country. At the moment I am only really interested in the POTS types, but that may change as I go deeper into this. I found a very engaging article describing how the earliest American telephones were wired for a shared party line. I think it's likely that in Australia we inherited features of both British and American systems. The choice of colours for the primary line pair in the US (green positive, red negative) seems counter-intuitive to us down under, but that may be due to subliminal associations in the US, such as green = go, red = stop. Whereas, since our AC mains originally utilised the red (active) black (neutral) and green (earth) system, we wouldn't feel comfortable with thinking of green as a positive wire. Just speculation, but may be in fact informed by WH&S principles.
    A friend tracked down a standards document which confirms that the normal practice was to make the primary pair for a single domestic line white ('tip' positive) and blue ('ring' negative). But in my case and that of a friend, the blue incoming wires to both our residences read relative positive voltage (and white is negative). Neither of us has any fancy arrangement which would require reversing the polarity. So I conclude this may be sloppiness on the part of the installer, perhaps. Here's an except of our standards confirming that the white should be positive.
     

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  4. Bluejets

    Bluejets

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    698
    Oct 5, 2014
    Early Australian phones were party line.
    As for the polarity as Kellys-eye says, no matter.
    Now with NBN, even less if that's possible.
     
  5. Cutty Shark

    Cutty Shark

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    Nov 11, 2018
    I'll be over to NBN a week from now. So I'll be able to check that out. (i put things off due to concerns about issues with ongoing infrastructure work by Vision Stream in my area). I gather the smartmodem has a DC telephony emulator that provides the same kinds of signals supplied by the traditional battery system, and can work with an integrated answering service module.
     
  6. Bluejets

    Bluejets

    3,452
    698
    Oct 5, 2014
    Depends on your supplier.
    Some modems will operate with single line and 2 inputs for preference such as alarms, lifts etc. others will not and will require you to pay for 2 lines into your premises.(domestic)

    At times, NBN ain't all it's cracked up to be.
     
  7. Cutty Shark

    Cutty Shark

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    Nov 11, 2018
    I'd have to say I agree. It's been implemented too quickly. The speeds I was getting up to now were perfectly adequate for my needs, and probably would have been for years henceforth. The new Smart modem has two domestic phone outputs, but will operate on a single input line from the street.
     
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