What must be disconnected before using a twisted-pair cable tester for UTP cables?

To effectively use a twisted-pair cable tester for Unshielded Twisted Pair (UTP) cables, it is essential to disconnect customer premises equipment from all jacks. This ensures that the tester can accurately assess the integrity and connectivity of the cabling without interference from active devices that might alter the results.

When customer premises equipment is still connected, the signals or data traffic generated by those devices can introduce noise or result in false readings, making it challenging to determine whether the cabling itself is functioning correctly. Disconnecting all devices allows the tester to provide a clean and precise evaluation of the cable connections, wiring patterns, and potential faults.

In contrast, leaving network interface devices or telecommunications service lines connected may not directly affect the ability of a cabling tester to work, but it does introduce potential sources of error. Similarly, power adapters for networking devices do not directly interfere with the testing of the cabling itself, but it's still critical to focus on the cabling under test conditions.