telephone line ?

Thread Starter


Joined Jul 21, 2008
How long can the telephone line from the POTS incoming box (telecom service box ) to the building or houses wall jacks be.

Basically I am trying to figure out at what length running telephone line and how many splits of the line to different wall jackets can be until the signal is lost or needs to be amplified?

For houses I would imagine if your not in a mansion then there probably won't be to much need for amplification but tall buildings that used or uses to uses telephone lines connected to the POTS system I would imagine at some point of the run ... floor 8 or what ever you would need to amplify the signal somewhere with a telephone signal/voltage amplifier

Curious how big building installations did it. I know they used 66 blocks , voice messaging systems and pbx systems on the first floor but what I don't fully get is long wire runs would still need amplification. So I am curious how they did this amplification. (the question is similar to running electricity on longer distances one needs to up the gage wire as well as some times install voltage regulators or transformers to the mix)

Is it amplified after the 66 box some where or is the pbx box have an amplifying device built into it even so I would imagine the length of the telephone cord runs would still need to be amplified for long running cord.

The installing of a 66 or 110 block or voice messaging system or pbx box is not the issue here it is the length of telephone cord runs and number of splits that I am worried need amplification at some length...

Or maybe they install pbx/voice messaging boxes on multiple floors to solve the amplification issue sort of like a router/switch on every floor connected together if we are taking the computer network example. Seems like the most logical guess for big building back in the day.

But for huge homes and non-pbx/non-Internet (asterisk) pbx based phone systems huge buildings I am curious on...
Last edited:


Joined Jan 25, 2013
Not sure about other countries, but here in Australia we use standard 600 Ohm Groun-Loop POTS systems.

To add a bit of scope, this is a sparse country. Exchanges are few and far between, and your cable length (exchange to home) can be as far as 7KM. Within that length, the exchange wiring comes out in bundles of 1,000 to primary distribution pits where they are joined (either soldered or crimped) to other 2nd-level distribution cables and sent off to the next pit, and so on, and so on until it reaches the pit/node that has the cable that services the street the house in question resides.

Typical POTS services run at around 50 volts, and over such large distances the POTS service is very much still effective (unless you get water in the pits etc..). If the cabling is poor or if the run is extensively long (> 7KM) we can install coils in the pits (essentially isolating transformers) and switch the exchange to a higher voltage (100-150V) that steps down to normal POTS voltages at the coil before reaching the CPE. These are mostly phased out now as they kill ADSL signals.

So as to your question, being an 8, or even 50 floor building. Another couple hundred meters isn't much in the scheme of things.