 Can you join Cat5 cable together? In many cases, it is recommended not to join any data cables, but rather a place with a new dedicated link. However, in some cases, it is more sensible to join. There are two main ways to join a Cat5 e-cable. 1. Through coupler. 2. Inline joiner. The through coupler is achieved by plugging in two RJ45 plug ends into each side. This then creates an extension. In contrast the inline joiner is a single block with two termination points similar to a module. The cables are punched down on either side of the joint box. Thus creating a permanent joint. The coupler solution is known for large transmission loss through the joint and will in a large amount of cases fail once tested with a fluke tester. The inline joiner in nearly all cases will pass as good as a new cable. Therefore the coupler is usually only recommended for a quick fix until a pen and replacement is done.