Electromagnetic interference of T1 lines

Q: Core Communications is an Internet service provider, and I`m the "cable guy" in the company. We are remodeling our offices, and I will be installing several temporary T1 1.554-megabit-per-second circuits from an old location to the new wiring center within the same building. These circuits will remain active until our telephone company relocates the demarcation point to the new main crossconnect and we can make the cutover. The length of the temporary run is 90 feet. My question is about the electromagnetic interference requirements of T1 lines. I have been told by some "old" telephone company folks that T1 lines are often separated into separate bundles--one to transmit and the other to receive. Can you advise me on this or suggest a source of information?

Jeffrey Fritts

Core Communications

Anchorage, AK

A: The "old telco folks" are correct. My guess is that you will be extending existing T1 lines, not installing new lines from the old to the new demarc; hence, you will be adding 90 feet to the end of what may already be 9000 feet of 26 AWG or 12,000 feet of 24 AWG copper cable. The copper outside-plant cable coming into your site could be either one large sheath cable (with the T1 transmit pairs in one binder group and the receive pairs in a nonadjacent binder group) or a screened cable. Either scenario can be extended by placing two--minimum Category 3--cables from the old to the new demarc and maintaining the same separation pattern as your service provider.

If you are looking for a good tutorial on transmission, I suggest you read bicsi`s Telecommunications Distribution Methods Manual, Chapter 26--Principles of Transmission.