Why you might not want to join two Ethernet cables (and what you should do instead)

An RJ45 coupler can join two Ethernet cables quickly and usually without affecting speed, but it adds a connection that could become a fault point. For a permanent run, a single cable of sufficient length is simpler; when several devices need wired access at the far end, a network switch is more suitable.

The copper Ethernet channel limit is 100 metres, including patch cords, and a coupler does not extend it. In tests of specific Cat6 and Cat6A combinations, most setups with three couplers passed, one received a marginal result, and setups with four failed, though this is not a universal threshold. Good Cat5e or Cat6 cable is generally enough for Gigabit connections; an unmanaged five-port Gigabit switch costs around $15, but needs power and does not provide Power over Ethernet unless designed to do so.