How to Troubleshoot Your Telephone Wiring

Technical Tips for Locating the Problem Yourself

By
Timothy Thiele
Timothy Thiele

Timothy Thiele has an associate degree in electronics and is an IBEW Local #176 Union Electrician with over 30 years of experience in residential, commercial, and industrial wiring.

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Updated on 05/25/22
Reviewed by
Larry Campbell
Larry Campbell
Reviewed by Larry Campbell

Larry Campbell is an electrical contractor with 36 years of experience in residential and light commercial electrical wiring. He worked as an electronic technician and later an engineer for the IBM Corp. is a member of The Spruce Home Improvement Review Board.

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Senior woman sitting in bed, using telephone
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Landlines are nothing if not reliable, but things can still go wrong with your old-school communication system. In most cases, it's a faulty wire connection or something equally simple to fix. Understanding the basics of your telephone wiring system will help you track down the problem and make the repair. It's also important to know which parts of the system are your responsibility and which parts belong to the phone company (which they will fix, usually for free).

Phone System Basics

The phone company owns and maintains the telephone lines (wires) that bring phone service to your house. The lines usually connect to the house at a gray plastic box mounted to an outside wall. This box is called the NID (Network Interface Device). Inside the box, the connections may split into two parts, the utility (phone company) side, and the customer side. Although you can access the customer side of the box, the phone company side has a special screw that's designed to be difficult to remove; it's best to leave this side alone. The NID is the standard demarcation point.

Inside the House

Beyond the demarcation point, the phone wiring may lead to a junction box that serves as a switchboard for multiple lines running throughout the house. Each line may lead to one or more phone jacks. If there is a problem on one phone and not the others, examine this phone's jack and line back to the junction box. Older phone systems may have a single line that connects to all of the jacks in the house. If this one line is damaged at any point, all of the phones may be affected. With either setup, any of the lines can be split en route to any jack so you may find splitters or mini junction boxes between a jack and the main junction box or the demarcation box.

Locating the Trouble

First, you need to know where the problem lies. Start at the demarcation point (NID) or the customer side of the exterior telephone junction box. Try plugging your telephone into one of the phone jacks in the junction box. If there is service (a dial tone) that sounds normal, the problem lies somewhere inside the home. If you have noise on the line, dead air, or a buzzing sound, it's the phone company's problem to fix. At that point, simply call the phone company for repairs. If not, read on.

Possible Solutions

Technical Tips
Problems Causes Fixes
Buzzing on the line Incorrect wiring or wires touching metal Check for proper wire colors and connections.
Static on the line Phone line wires wet or have loose connections Check the wires and inside the phone jack covers for signs of moisture.
No sound on the line; "dead air" Wire off, wire crossed, or wire is shorted to another Check phone jacks to see if wires are touching each other; it is often bare wires touching.