Once you have terminated cable, you must test it to ensure that each wire makes good electrical contact and is in the correct pin position. The best time to verify wiring installation and termination is just after you have made all the connections. This means you should still have access to the cable runs. Identifying and correcting errors at this point will be much simpler than when you are trying to set up end user devices.

You can use several cabling and infrastructure troubleshooting devices to assist with this process.

Cable Tester

A cable tester is a pair of devices designed to attach to each end of a cable. It can be used to test a patch cord or connected via patch cords to a wall port and patch panel port to test the permanent link. The tester energizes each wire in turn, with an LED indicating successful termination. If an LED does not activate, the wire is not conducting a signal, typically because the insulation is damaged or the wire isn’t properly inserted into the plug or IDC. If the LEDs do not activate in the same sequence at each end, the wires have been terminated to different pins at each end. Use the same type of termination on both ends.

Toner Probe

Many cable testers also incorporate the function of a toner probe, which is used to identify a cable from within a bundle. This may be necessary when the cables have not been labeled properly. The tone generator is connected to the cable using an RJ45 jack and applies a continuous audio signal on the cable. The probe is used to detect the signal and follow the cable over ceilings and through ducts or identify it from within the rest of the bundle.

Disconnect the other end of the cable from any network equipment before activating the tone generator.

Loopback Plug

A loopback plug is used to test a NIC or switch port. You can make a basic loopback plug from a 6” cable stub where the wires connect pin 1 to pin 3 and pin 2 to pin 6. When you connect a loopback plug to a port, you should see a solid link LED showing that the port can send and receive.

A loopback plug made from a cable stub is unlikely to work with Gigabit Ethernet ports. You can obtain manufactured Gigabit port loopback testers.