A “demarcation point” is a piece of equipment that separates the telephone company’s wiring from your own wiring. All wiring outside the house up to and including the demarcation point is owned by and is the responsibility of the telephone company. All wiring from the demarcation point inwards to the rest of your premises is owned by, and is the responsibility, of the homeowner.
A demarcation point also serves as a surge protector, lightning arrestor, and junction box for telephone wiring.
You can usually find a demarcation point in any of the following locations:
In many newer installations, you can also find a telephone jack immediately adjacent to the demarcation point. It may be labelled with “test jack” and/or your telephone number. In some cases, your inside telephone wiring may be plugged into this jack. This jack is useful for testing when you run into telephone or Internet service problems (if your Internet service is being delivered over the phone line).