How should a digital multimeter (DMM) be used to troubleshoot problems in telephone wiring?

Using the voltmeter function of a digital multimeter (DMM) is essential for troubleshooting problems in telephone wiring because it allows you to measure the voltage levels across the wires. In a typical telephone circuit, you expect certain voltage readings that indicate whether the line is live and functioning correctly. By measuring the AC and DC voltages, you can determine if there is a proper voltage supply, which is crucial for the telephone operation.

When there is an issue with the telephone line, such as a dead line or poor call quality, checking the voltage can help diagnose whether the problem lies with the wiring, the telephone equipment, or the service provider. A healthy line will show voltage even when not in use, while a faulty line could show zero or significantly reduced voltage, pointing to potential problems like shorts, opens, or other disconnects in the circuitry.

Other functions of the DMM do have their uses, such as checking resistance to identify breaks, using continuity to confirm that the circuit connects, and frequency measurements for signal integrity, but for immediate troubleshooting of voltage issues in telephone wiring, the voltmeter function is the most critical.