telephone twin line

[martin.shaw11]

How can two phones with two seperate numbers be supplied by just two wires ? Are there some filters somewhere ?

[Andy Burns]

DACS ISDN/2 or HomeHighway PSTN with ADSL with VoIP in ye olden days party line, was that 2 wires plus local earth or 3 wires back to exchange?

[Frank Erskine]

The party line (later known as "shared service") was two wires and a local earth. Instead of ringing current being applied across the two wires it was sent over one or the other wire with an earth return. Outgoing calls were originated by the calling party pressing a "call exchange" button to send the local earth to one wire or the other.

In a very few instances where it was impractical to get a local earth at the sub's premises a "semi-local" earth was achieved at the local distribution point (DP) (usually a "telegraph pole!") which always had an earth connexion.

If you were really clever you could rehash the setup to make your outgoing calls as if they were from your very old next-door neighbour you shared the line with, who would never dream of querying her bills... Or so Im told.

[Owain]

2 wires plus local earth.

Owain

[Dave Plowman (News)]

Party lines really weren't twin lines. Although the metering worked for the correct subscriber, they were just like one line as far as the users were concerned. Pick up your phone while the 'other side' was in use and you heard everything.

[Andy Burns]

We used to have one back in the 70's, new housing estate presumably overstretched the capacity of the GPO wiring ...

[Andy Wade]

Easily 'fixed' with a simple modification to the wiring so that the other party paid for your calls. One of the reasons they were phased out...