CAT 5 cable wiring configuration

[jim6918]

I seem to remember reading somewhere that either 568-A or 568-B Cat 5 wiring configuration would work with LOR, but searched and can't find it anyplace.

Anybody know which is better? Or, both the same? Are all pins used on the connector?

[testraub]

Either will work as long as you don't try a cross-over cable. I don't think all the wires are used, even in a ethernet enviroment. Not sure but I think the rs485 doesn't use them all, but if your buy Cat-5 cables they come with a RJ-45 on each end. I make my own cables and use the 568-8 for mine. I can use the cable for running a line out to my shed if I don't want to use the Wi-Fi.

Tom Straub

[Paul Roberson]

Yes, either will work.

LOR uses:

Pin 3 is +9vDC for powering ELLs and other LOR devices

Pin 4 +

Pin 5 -

Pin 6 ground

[jim6918]

Thanks guys, Just wanted to make sure before I made up some cables and wasted the connectors.

[Steven]

jim6918 wrote:

I seem to remember reading somewhere that either 568-A or 568-B Cat 5 wiring configuration would work with LOR, but searched and can't find it anyplace.

Anybody know which is better? Or, both the same? Are all pins used on the connector?

568-A and 568-B are electrically identical. The only difference is which colors go to which pins. If you buy complete cables, it doesn't matter. The only time you would need to know is when you need to make a repair "in the field" by cutting the cable and crimping a new connector.

568A and 568B both specify 4 "pairs". Pair 1 is blue/white; pair 2 is green/white; pair 3 is orange/white; and pair 4 is brown/white.

Pair 1 connects to pins 4 & 5; Pair 4 connects to pins 7 & 8.
In 568A, pair 2 connects to pins 3 & 6, pair 3 connects to pins 1 & 2.
568B is reversed.

10BaseT and 100BaseT (both are Ethernet) use pairs 2 and 3. If the cable is wired 568A on one end and 568B on the other, then you have a crossover Ethernet cable. This may work with LOR as the data + and data - pins are still connected, but the signal ground pin will not be connected, which could cause problems. (I haven't tried.)

Sometimes you can buy (older, cheaper) Ethernet cables that have only pairs 2 and 3 (pins 1, 2, 3, and 6). These will not work with LOR.

[-klb-]

From what I see reading about RS-485 troubleshooting, it will often run for a few minutes, or even longer with no signal ground. But eventually it normally builds up enough charge, and corresponding voltage offset that communication becomes unreliable without the signal ground.

The strongest reason I can provide for hooking up all 8 wires is that the strain relief crimps on cat5 connectors are often really poor. So having all 8 wires connected, instead of just 4 makes the connection to the cable that much stronger. Also, Gig E uses all 8 wires, so if you might ever reuse the cables in a gigabit network, it makes sense to wire them out.


One more comment: TIA-568A is more common in telco based wiring schemes, while TIA-568B is more common in data centric wiring schemes. I'd say 90% of the cables I've ever worked with have been TIA-568B, even having worked for a telecom services company in the past. So I would recommend leaning TIA-568B, in case you ever wind up shortening pre made cables, it is the scheme most likely to produce a correct cable. Of course, you really ought to check the other end when shortening any cable.

[Jim Saul]

Steven wrote:
[sometimes you can buy (older, cheaper) Ethernet cables that have only pairs 2 and 3 (pins 1, 2, 3, and 6).  These will not work with LOR.


The day my first CCR arrived I connected it and nothing. 1/2 hour later I figured out the patch cord I grabbed was one with only 2 pairs terminated.

[jldavis1969]

Me being in the computer field, 10base-t and 100base-t do use 2 pair of wires. But 1000base-t or gigabit network use all 4 pairs of wire in a cat-5e cable.

[Max-Paul]

Well I dont think we will see giga-byte speeds any time soon with LOR hardware. But I have to pose a slightly deeper question. As you all know that have ever worked with Cat 5 or higher cable. That all 4 pairs have a different twist rate. Part of this is to keep the wires from laying closely to each other and having what is called cross talk.

But if you know your electronics, a twisted wire will act as a cap. So, if you have a differential noise on a pair, the twist will help null this noise. So, I wonder in a network setting if it would be better to use the B configuration versus the A due to the twist rate.

But back to earth. A or B does not really matter other than both ends of the cable is the same configuration as pointed out by other.

[-klb-]

I've used cable test tools that will certify cat6 patch cable, which is a more stringent test than the cat6 channel test. I've not seen anything in the test results, or literature to suggest that it matters which pair has what twist rate. (though the test tool coud tell you which pairs propagated signal faster, implying the differences in twist rate) In fact, GigE adapters use all pairs in basically the same way.

The only thing I have seen is that some of the high end cat6 cable ends presume that the 4 pairs are in in a certain orientation to each other, in order to do 568B. With these ends, orange and brown must be 180 degrees apart in the cable, leaving blue and green 180 degrees apart in the jacket. I've run into a very small quantity of cable that was not layed out that way, so when building cables, I had to wire as TIA568A to get the correct results with that cable.

But for LOR, pick one of the standards, (TIA-568A, or TIA-568B) and run with it. Either will work.