To build a female loopback plug, you need to connect the terminal for pin 1 to pin 4 and pin 2 to pin 5. Here’s what else you need to make a female loop-back plug for a T-1 level circuit:
A standard category 5e (Cat 5e) jack: You can find Cat 5e jacks in the same general area as the RJ-45 connectors at your local home improvement or electronics store. Some Cat 5e jacks even come with their own push-stick to secure the wiring. The pin locations are listed on the side of the jack. After pushing the wires into place, simply cut off the excess and close the jack.
Crimping device: Refer to the previous section for more information about crimping devices.
Wires: Of course you need wires.
Tip Insert the RJ-45 connector into the CAT 5e jack to keep both of your valuable pieces of test equipment together. If you leave enough extra wire on the RJ-45 loopback, you can use the loop on the wires to hold the plug on a hook, screw, or nail in your phone room. This will ensure you have both connectors available for use and at the ready for whenever you need them.
Tip Looking for more information about setting up a loopback plug? Check out the following online resources:
The loopback devices listed here are specifically used to test T-1 level voice circuits. The same RJ-45 connector and Cat 5 jack can be used to test other types of circuits, but the pin configurations are different:
Loopback wiring for a 56K CSU/DSU: Wire to connect position 1 to position 7, and with the second wire, connect position 2 to position 8.
Loopback wiring for a FastE circuit: Wire to connect position 1 to position 3, and with the second wire, connect position 2 to position 6.