Single communication wire vs Cat5 with 4 twisted pairs. Interference?

I have several Arduinos networked together using just a single twisted pair wire (signal and ground) that I took from a Cat5 cable. That is I removed all the wires from the cable casing and took the 4 twisted pairs apart and used just a single twisted pair (2 wires). It works fine, even over distances about 25 feet.

I then took an entire cable with all 4 sets of twisted pairs in tact and used just a single pair for the same sort of connection and it failed miserably. Essentially I just wanted to keep the outer cable casing on because I was running this wire up above the ceiling so rather than strip it all and pull out just a single twisted pair, I just used the entire thing.

Because there are now 8 wires is that simply causing much more signal loss along the way? Or is there something else going on here? I'm still only using a single twisted pair of the 4 in the cable. The others are just empty ends.

Thanks.

I shouldn't have to ask, but, did you check the wires for continuity using and Ohmmeter? Did you put the RJ45 plugs on the ends of the cable?

Paul

The ungrounded conductors act as radio antennas picking up interference and coupling it to your signal wires.

I agree with mikb55.

Why dont you connect wire pairs in parallel so that the effective resistance is also reduced and earth any unused pairs.

Would be interesting to see the result.