TECHNICAL GUIDE
RJ45 is the everyday name for the 8P8C modular jack used for Ethernet — 8 positions, 8 contacts. The name is borrowed: the original RJ45 registered jack was a telephone interface with different keying. Nobody in the industry will misunderstand you, but a drawing that says 8P8C is being precise. Pin assignments on this page follow ANSI/TIA-568; pair usage follows IEEE 802.3. KINGCONN figures come from the drawings published on the part pages.
Looking into the jack with the latch slot down, the contacts are numbered 1 to 8 from left to right. The cable is 4 twisted pairs, and TIA-568 assigns them so that pins 3 and 6 belong to the same pair even though pins 4 and 5 sit between them. That split pair is not a mistake — it keeps the jack backward compatible with older telephone wiring, which is why you must never rewire 3 and 6 to be adjacent.
Pairs on pins 1 and 2, and on 3 and 6, carry 10BASE-T and 100BASE-TX. 1000BASE-T uses all 4 pairs in each direction at once, so the pairs on 4 and 5 and on 7 and 8 stop being spare the moment the link negotiates gigabit.
TIA-568 defines 2 wiring schemes. They differ only in that the green and orange pairs are swapped:
Either scheme works as long as each end of a cable uses the same scheme. Mixing schemes end to end produces a crossover cable, which modern equipment auto-corrects and which therefore hides the wiring error until you connect something that does not. Pick a scheme for the site and put it on the drawing.
Ethernet needs transformer isolation between the PHY and the cable. You can put discrete magnetics on the board, or buy a jack with the transformer inside it. The integrated jack costs more per piece and saves board area, placement steps and a set of layout rules that are easy to get wrong.
KINGCONN publishes each style. 7RJ45-F0-0002 is a plain jack; 7RJ45-A0-1005 is a 1000BASE tab-down jack with transformer, LEDs and PoE support; 7RJ45-F0-0049-1 is a 100/1000BASE jack with transformer. If your design draws power over the same cable, the jack has to be specified for it — this is not something you can add later with a different cable.
Tab orientation decides which way the cable latch faces on the finished panel, and it is fixed by the part: 7RJUS-F0-0008 is a tab-up part that also carries a USB 2.0 port in the same body, for panels where the 2 interfaces sit together. Jacks with LEDs bring the link and activity indicators out through the front bezel, so no separate light pipe is needed. Port count is part of the housing: 1x1 and 2x1 versions exist in the catalog.
Mounting is through-hole or SMT — 7RJ45-F0-1101 is the SMT part. Through-hole is still normal for panel-edge jacks because the pin retention takes the cable insertion force. A sealed circular version is listed for outdoor equipment.
KINGCONN RJ45 jacks are published at 750 mating cycles minimum. That number is low next to a memory card socket, and it is the right order for the application: a fixed installation sees the cable inserted rarely. Housings are glass-filled PBT or PBT with LCP rated UL94V-0, contacts are copper alloy, RoHS compliant.
The catalog lists 9 RJ45 parts, shielded and unshielded, with and without transformer. For the wider board-end I/O question see industrial I/O connectors, or the networking equipment solution page for how these sit alongside the rest of a switch or gateway build. Send your speed, PoE and panel requirements to service@kingconn.com.tw.
Standards referenced: