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I found among my Ethernet cables one that has only 4 wires connected within it. the connection is straight and connects the following wires:

blue at pin 3
blue/white at pin 6
orange at pin 7
orange/white at pin 8

What is this type of wiring used for?

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    telephony? most telephone cables are 2-Pair bundles. RJ45 vs RJ11 is just a choice. also note that anyone who can write a driver can implement a different pin-mapping/wiring scheme so it could be proprietary. I think I have a USP that connects to the UPS with a 2Pair RJ45, but the other end is USB-A. if you have low level control of one or both sides of the connection, you can do whatever you want with the wiring.
    – Frank Thomas
    Commented Apr 12, 2020 at 8:15
  • Is there anything written on the cable itself?
    – grawity_u1686
    Commented Apr 12, 2020 at 8:55

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Lacking any other information about the cable itself, I'd guess it could actually be Ethernet.

Earlier twisted-pair Ethernet standards (for 10 Mbps and 100 Mbps) only used two pairs for data transfer – pair 3/6 was used for receiving data from hub/switch to host, pair 1/2 (not 7/8) for sending data to hub/switch. The other two pairs were completely unused and often the Ethernet ports even physically lacked the pins.

This meant some manufacturers would decide to save on copper by not putting the unused pairs in cables in the first place. (Although, if it really was meant to be Ethernet cable, the standard pair colors would be orange and green instead.)

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  • thanks. it is very much possible that this is indeed an old cable. is there any resson today to keep such a cable?
    – epeleg
    Commented Apr 13, 2020 at 14:08

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