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Maximum length of a single twisted pair run

Does anyone know what the maximum length of a twisted pair should be?  I am terminating an analog device on the top floor of a building to a vg224 in a basement and am trying to figure out if it's too far.

2 REPLIES
Hall of Fame Super Red

Re: Maximum length of a single twisted pair run

Hi Shikamaru,

Hope life is good my friend!

We use the VG248 (the VG224 older brother to supply an Analog  device at one of our Grounds Buildings which is at least 600m away. This  is via a Tie Cable (26 gauge wire). The max distance listed by Cisco is  975m for a phone with 1 REN. The specs are for the ATA, but the VG's  are very comparable. Have a look;

This info is from an old Cisco doc;

Q. What is  the maximum distance from which I can drive an analog device with a  Cisco ATA?

A.  Table below provides maximum distances for this question.

Ring Loads  and Distances

Ring  Load (per RJ-11 FXS Port) Maximum Distance

5 REN 200 feet (61 m)

4 REN 1000  feet (305 m)

3  REN 1700 feet (518 m)

2 REN 2500 feet (762 m)

1 REN 3200 feet (975 m)

**Here is  the actual reference for the VG224;

Loop Length

3000 ft, 26 AWG

http://www.cisco.com/en/US/prod/collateral/voicesw/ps6790/gatecont/ps2250/ps5516/product_data_sheet09186a00801d87f6.html

Ringer  equivalence number

In telecommunication, a ringer equivalency number (REN) is  a somewhat arbitrary number which denotes the loading a telephone  ringer has on the line.

A ringer equivalency number of 1 represents the  loading effect of a single "traditional" telephone ringing circuit, such  as that within the Western Electric Model 500 desk telephone. Note that  modern telephone equipment may have a REN significantly lower than 1:  as a rough guide, externally-powered digital-ring phones may have a REN  as low as 0.2, while modern analog-ring phones (where the ringer is  powered from the phone line) typically have a REN around 0.8.

The total  REN for a subscriber's line is simply the sum of the RENs of all devices  connected to the line; this number expresses the overall loading effect  of the subscriber's equipment on the central office ringing current  generator. The local telephone company usually sets a limit on the total  REN, typically 5 or less.

If the total allowable REN load is exceeded, the  phone circuit may fail to ring (or otherwise malfunction). In extreme  cases, the telephone service provider may temporarily disconnect an  overloaded line to reduce load.

While REN is a United States-developed  yardstick, analogous systems exist internationally. In some countries,  (particularly in Commonwealth nations), the REN is better known as the  ringer approximated loading number (RAL). In the United Kingdom it is  called the ringer equivalence number and a maximum of 4 is allowed on  any British Telecom (BT) line.

From Wikipedia;

http://en.wikipedia.org/wiki/Ringer_equivalence_number

Hope this  helps!

Rob

New Member

Re: Maximum length of a single twisted pair run

Hey Rob, how's it going buddy   Top form as usual, thanks for the speedy reply.  Much appreciated as always, friend.

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