A phone jack is a device that allows a telephone set and other similar telecommunications devices to connect to a telephone service via the telephone cable. Phone jacks are constructed and wired according to a physical interface standard called registered jacks (RJ). Phone jacks provide convenience, but these devices often break down because of abuse or misuse. Learn how to test a phone jack to know if it is working before calling in a handyman to replace it.
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Go outside your home and look at the telephone cable that runs from the utility pole into your premises. Follow the cable until it reaches the network interface device, or NID, which is a small plastic box (colored gray or tan) that your telephone service provider places just outside your home. Open the box by loosening the holding screw in front of the box.
Find the short wire (beside the terminal screws) terminated by a modular connector and plugged into a telephone jack inside the NID. Unplug the modular connector from its jack. Get a working phone and plug it into the jack. Lift the telephone handset and listen for a dial tone. The absence of a dial tone indicates that there is no power or signal coming from the phone company. It also indicates that the telephone jack is not the source of the problem. Call the telephone company to report the absence of a dial tone. Proceed with the next steps if there is a dial tone.
Get the working phone that you used to test the NID jack in Step 2, and plug the phone into the jack you are trying to test. Lift its handset and listen for a dial tone. Since you already know through previous tests that the telephone including its plug is working, and that telephone power and signals are flowing from the NID to the telephone wires leading to the jack, the absence of a dial tone is indicative of a non-working jack.