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Do-It-Yourself (DIY) Question & Answer Forum
main earth to house through a BT circuit.
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<blockquote data-quote="SPECIAL LOCATION" data-source="post: 15301" data-attributes="member: 250"><p>3rd wire?????? ?:| </p><p></p><p>telephone circuits have been 2 wires for donkeys years....</p><p></p><p>the internal wiring of the bell circuit inside the old type telephone created a "third connection (wired)" inside the phone..</p><p></p><p>To wire two or phones in parallel you used to have to modify the internal wiring of the phones to stop the "Back tinkle" when one telephone was dialling a number and could cause the parallel phone to sound as though it was ringing!</p><p></p><p>With modern LJU's the bell capacitor is inside the master socket, and</p><p></p><p>the third wire has to be continued through to all of the secondary sockets is so that any old-type phone can still get the ring current via the bell capacitor which is connected between pins 2 &amp; 3 on the LJU.</p><p></p><p>The ring appears to only be on the one wire.. because the other one is with respect to earth at the exchange..</p><p></p><p>The earth reference was also exploited in the old days with the Party line system..</p><p></p><p>where two houses had a telephone each over the 2-wire circuit sharing a common earth return.</p><p></p><p>(bit like stereo headphone L-R &amp; common return.)</p><p></p><p>But both phones could not be used simultaniously....</p><p></p><p>here endeth todays telephony history lesson..</p><p></p><p>next time we meet class can you bring your homework in.</p><p></p><p>remember we needed pictures of the uglyest telephone you can find..</p><p></p><p>and a handwritten copy of all entries under letters J-K from your local phone directory:O:^O:^O:^OGuiness Drink</p></blockquote><p></p>
[QUOTE="SPECIAL LOCATION, post: 15301, member: 250"] 3rd wire?????? ?:| telephone circuits have been 2 wires for donkeys years.... the internal wiring of the bell circuit inside the old type telephone created a "third connection (wired)" inside the phone.. To wire two or phones in parallel you used to have to modify the internal wiring of the phones to stop the "Back tinkle" when one telephone was dialling a number and could cause the parallel phone to sound as though it was ringing! With modern LJU's the bell capacitor is inside the master socket, and the third wire has to be continued through to all of the secondary sockets is so that any old-type phone can still get the ring current via the bell capacitor which is connected between pins 2 & 3 on the LJU. The ring appears to only be on the one wire.. because the other one is with respect to earth at the exchange.. The earth reference was also exploited in the old days with the Party line system.. where two houses had a telephone each over the 2-wire circuit sharing a common earth return. (bit like stereo headphone L-R & common return.) But both phones could not be used simultaniously.... here endeth todays telephony history lesson.. next time we meet class can you bring your homework in. remember we needed pictures of the uglyest telephone you can find.. and a handwritten copy of all entries under letters J-K from your local phone directory:O:^O:^O:^OGuiness Drink [/QUOTE]
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main earth to house through a BT circuit.
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