What is “TEL” on a Fax Machine?

LAST UPDATE: April 18th, 2019


“TEL” on a fax machine or fax modem can be:

  1. The port connects to a phone jack (sometimes labeled “LINE“).
  2. The port connects an extension telephone (sometimes labeled “EXT“).
  3. In the context of “FAX/TEL,” a switch that changes between fax and telephone modes.


A “TEL” port on a fax machine is confusing. It is a port to connect to either the phone jack in the wall or to add an extension telephone so that there can be a fax machine and another telephone on the line.

If there is one port for a phone line labeled “TEL,” it is for the phone line.

If there are two ports, one of which is labeled “TEL”…

  • … and the other “EXT,” then the “TEL” port is to connect the fax to the phone line, and the “EXT” port for an extension telephone.
  • … and the other “LINE,” then the “TEL” port is to connect an extension telephone (an extra phone that can use the same line) and “LINE” for the line to the phone jack.