Network Cable!

If you are talking about Ethernet (RJ-45), then you will find that the other 4 are ground - to reduce noise. If your talking about some other type of network cable - ditto.

Hello Zirkond

It's the same reason that shows if you open a Computer case, and look at the flat cables run from the Motherboard ATA/IDE sockets to Disk Drives, CD-ROM Drives, DVD-Drives and so on.

There are 2 types of flat ATA cable, the earlier 40 wire and improved/later 80 wire.

Always use the 80 wire, then set the drive on CS = "Cable Select", because as explained by Kilowatt0 above, the alternate wires are grounded, to prevent interference = talkback, via capacitance/inductance between the signal wires.

It was first proposed that each wire be individually shielded, then the bare shield of each wire covered in insulation, but the cable makers won the day, because they pointed out the extra costs involved with all that shielding + Insulation, were dearer than using the extra wires.

As far as the ATA/IDE system to Drives in a Computer goes, it is being replaced by the SATA system, without all those parallel wires.

That is because CPU and other Hardware speeds are now far above the ability to transfer data quickly by means of the PATA/ATA/IDE (Parallel) data transfer system.

Kind Regards....

I cannot ad more to kilowatt0 and sparky other than that you must pull the wire during heavy thunder activity. The network card seems to pop very fast. I was without internet and CR4 for a week.

I have network cables running for 20m to my outbuildings and it seems to form a loop with electricity or ground wires.

Those "free" pairs have a reason, not grounding but power.

The Ethernet standard did do a great job when estabished: they took into account that some day in the future appliances consume so little that they can be powered through these little conductors.

Check Mobotix they have PoE IP camera's that deliver great high quality images and movies.

It is a good attitude to ground conductors when not used, otherwise they can start playing antenna.

Very good question, and, surprisingly I find myself disagreeing with Kilowatt0 and Sparkstation. The unused wires are not usually earthed. They are unused:-

http://www.ertyu.org/steven_nikkel/ethernetcables.html

Many places sell splitter/combiner connectors which enable you to double up the usage of structured cabling:-

http://cpc.farnell.com/jsp/search/browse.jsp;jsessionid=VT5Z3OSMVHB4HQFIAFNZK0Q?N=411&Ntk=gensearch_003&Ntt=cable+economiser&Ntx=&_requestid=388283

Aren't more than 4 used for Gigabit over ethernet?

In full duplex Gigabit ethernet all 4 pairs or 8 wires are used. In old cat5 wiring people only pins 1,2,3, and 6 were used.Also with POE those other pairs are used.

Gigabit ethernet needs all 4 pairs so there are no spares when using 1000Base-T.

PoE (Power over Ethernet) uses the same lines in Mode A as the data transmission in 100Base-T, so you could get by with only 2 pairs. In Mode B it uses the spare connectors and needs all 4 pairs. This does not affect the ability to use 1000Base-T.

Now I'm little confused, because Hendrik, Sparkstation, Kilowatt0, say something different from Randall, Gwen.Stouthuysen.

what i should think.?

Now i add one more question maybe can help you.

Some of switch, router, and hubs have only 4 pins 1,2,3, and 6 contacts. And work very well!

If 4.5.7.8 are used for grounding, and hubs don't have, if they are used to ground, to reduce noise how can they do. ?

Thank you! And please your comment are very helpful to understand for economic reason.

If you are using 10Base-T or 100Base-T communication, then you can use the spares for whatever you want. They are spare lines and not grounded. If you use 1000Base-T, also known as Gigabit Ethernet, there are no spares. They are all used. If you have even 1 NIC with Gigabit Ethernet, you do not want to use the spares for other purposes.

If you plan on using the spares for power, there is a standard for that.(IEEE 802.3af) I think using PoE you can supply power to Ethernet peripherals like routers but you have to mind your distances as there is a bit of resistance in such a small wire and there is a voltage drop. They are talking about a new future standard that can supply more current for applications like Web cams and thin clients. That way you can use ethernet like USB. One cable for everything. (IEEE 802.3at)

I'm also a bit astonished on the different answers, there seams to be no universal system on the usage of the pairs in the Ethernet cable.

Last I had a jolly experience: A Beckhoff C1010 PLC refused connection with a network on wich I could log on with several computers and a WAGO PFC. We tried everything, even a cross cable.

Then we tried to check what happend when keeping the fixed line to the switch active. We installed a local switch and hooked a PC to this switch, then we connected the PLC to the local switch and immediatly all worked fine. I assume that the grounding/not grounding of one of the pairs at the original fixed line caused the network card of the Beckhoff PLC to refuse connection, the switch accepted it and offered the correct combination to the PLC. (each time for a fraction of a second it tried to establish the connection but it always resulted in a message that the cable got unplugged)

Did anyone of you had a same experience?

Hello Gwen.Stouthuysen

<"Did anyone of you had a same experience?">

Sadly yes, several times, and have always gotten around it the same way, with a local Ethernet switch.

There are 2 different methods of wiring a Cat5E cable, which also has caused difficulties here in the past.

Kind Regards....

You could try this dongle:-

Note that it's easiest if the slave equipment has a shielded (0V) RJ45 socket, but, that the shield does not need to extend beyond the centre tap of the transformer. If the socket is not shielded you could take a separate 0V wire from the equipment to the transformer.

This design assumes another transformer in the equipment. If you're designing onto the PCB then the centre tap needs to be capacitor coupled to the 0V.

What does this do? Prevents common mode noise (caused by different system grounds) jumping across the transformer in the equipment.

I would love to try it but the system is a remote unit approx 800km from my desk, and I rely completely on the functionality of the connection.

Can this be bought?

Zirkond,

Good question and interesting comments. There are many topologies for networks. Some require 4-pairs to work, but most only require 2-pairs. Most of the time, therefore, the other pairs are available as mentioned in previous posts. There is a surprising amount of engineering design in that simple looking CAT-5 cable. When you strip about a foot of its jacket off, you will notice that the closeness of the twists on each pair varies every few inches. This is one of many things done to improve its ability to transmit high-speed digital signals reliably (with minimal interference and noise). Perhaps a cable designer can give further information on this.

--JMM