Can you splice ethernet cable together?

T

timreichhart

Gawd
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Feb 22, 2009
Messages
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Hey Guys
I am just wondering if you can splice ethernet cable together? The reason why I am asking this because I need to add more ethernet cable to already placed ethernet cable. I plan on doing POE on this or should I just replace the whole ethernet cable?
 
Yes and no. TIA/EIA specs say you cannot splice the cable together. You'd need to use a switch or some other device in between segments. But in reality, sure you can splice it together, keeping in mind the 100meter length rule. I've done it before (running PoE on a 100' run) and it works fine. If you can, it is best to re-run the cable with a new one. In my case, the client's wall already had CAT5e run and no way to replace the cable without ripping the wall apart or use a splice.

Speaking of splices, this is what I used:
http://deepsurplus.com/Network-Stru...AT-5E-Junction-Box-110-Punch-down-Style-White
 
Well see this is going to be outside and I forgot to say that so its probably best to rerun the wire then. Because what I was thinking about using was using a keystone jack and cat5 plug.
 
I've done it before, a very dirty way. Soldered each individual wire together, wraped with electrical tape so they don't touch. It worked ok. Not that I'd advise that, but if that worked then the approved splices should work too.
 
I just decided just run whole new line just to be on the safe side but thanks everybody for your input and advice.
 
I use what sc0tty recommended... actually thanks sc0tty i think thats a better price then i normally pay for them. My guys used to just wire the wires togehter and put beanies on them. Then i found the splice box, and they LOVE them. They work great. I've used them outdoors without problems, as long as my wires in a conduit and the splice happens in a water-tight junction box.

Sure its best to have a straight cable without any splices, but hey this is the real world, sometimes you need a splice... try it, it'll probably work just fine.

Ive also done the keystone jack on one end, rj45 on the other in a pinch, as the junction boxes are like $3 each, keystone jacks are liek 80 cents each.
 
I've used a simple bread board for a couple months until i finally remembered to stop at home depot. No problems, full 1Gbps connection.
 
Can it be spliced? Maybe.

All copper-based ethernet standards use differential signalling at the physical layer. This is why you talk about the pairs in a network cable. Differential signalling sends an inverted copy of the exact same signal across the second wire. The advantage of using this is a. you don't need a common zero potential reference, b. it greatly reduces noise (the noise reduction is equal to the CMRR of the input stage, which is easily 60+ dB, and c. it greatly reduces the EM field radiated by the pair.

Whenever you punch down network cable, maintaining the twist as close together is a major concern. You only get the benefits of differential (aka balanced) signal transmission if the two wires are as close together as possible. You want the noise on each line to be basically identical. Furthermore, having the two wires close helps with cancelling out the EM field.

There's a lot of talk about how Ethernet cabling is susceptible to noise. Running ethernet near fluorescent lights or large power conduits is always a bad idea. Something that doesn't come up as much is that any high speed (copper) network cabling is going to be radiating eletromagnetic waves. Ethernet, on the wire, is a radio frequency signal. If you just have a single, unshielded piece of wire hanging between a NIC and a switch, that wire will be radiating RF, which will cause interference. There are two ways around this. The first way is to use a shielded conductor, for instance, coaxial cable. The shield will prevent electric fields from leaking out or in (of course, in the real world, shields aren't perfect. In high precision applications, usually for measuring current at the picoamp level, coaxial cable with two shields, called triax, is used). The other way is to use a balanced transmission line. The two electric fields, which are opposite in magnitude, will cancel out. However, the two wires have to be close together for this to work well. An example of a balanced transmission line (besides ethernet cable) is that plastic T-shaped antennas that come with FM radios. Two wires, about 1cm apart, encased in plastic. It's called twinlead.

So what's the gist of all this? Keep in mind when making a splice -- don't just worry about the network cable picking up interference, you have to consider the RF that it is going to radiate as well.
 
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