LAN Wiring & Pinouts

There is NOTHING more annoying than spending 30 minutes debugging a network problem to find it was the cable. Badly made or non-standard cabling is a foolish thing to spend time on - do it once and do it right. This guide may help you to forget cabling problems and spend time time doing really useful things - like pondering the meaning of life!

NOTES

1. LAN cables are generically called UTP (Unshielded Twisted Pair) and are identified with a category rating. When installing new cable, unless there is a very good reason not to, you should be using category 5, 5e or 6 UTP which is rated for both 10 and 100mb LAN operation.
2. You CAN use 100base-TX wiring with a 10base-T network (but not always the other way round). ALWAYS use 100baseTX/T4 wiring standards.
3. If you are using category 5, 5e or 6 wiring EVERYWHERE you can use the 100base-TX standard (this only uses 2 pairs , 4 conductors). Most of the information below assumes you are using category 5, 5e or 6 cables.
4. If you are using category 3 or 4 cables with 100M LANs ANYWHERE you MUST use the 100Base-T4 standard and this has ADDITIONAL RESTRICTIONS documented throughout (it uses all 4 pairs, 8 conductors). LAN connections/pinouts are defined by IEEE 802.3u.
5. Maximum LAN cable runs are 100 meters (~300ft).

Crossed and Straight cables - when to use them

The following diagram shows the Normal use of Crossed and Straight cables (see also the notes below).

Notes

1. We show Straight cables as BLUE and Crossed as RED. That is our convention the cable color can be anything you choose or more likely the vendor decides.
2. To avoid the need for Crossed cables many vendors provide UPLINK ports on Hubs or Switches - these are specially designed to allow the use of a STRAIGHT cable when connecting back-to-back Hubs or Switches. Read the manufacturers documentation carefully.

Category 5(e) (UTP) colour coding table

The following table shows the normal colour coding for category 5 cables (4 pair) based on the two standards supported by TIA/EIA.

10baseT Straight Cable (PC to HUB/SWITCH)

Straight cables are used to connect PCs or other equipment to a HUB or Switch.

The following cable description is for the wiring of both ends (RJ45 Male connectors) with the 568B category 5(e) wiring colors you could, of course, use the 568A colour scheme.

Pin No.	Strand color	Name
1	white and orange	TX+
2	orange	TX-
3	white and green	RX+
4	NC	*
5	NC	*
6	green	RX-
7	NC	*
8	NC	*

100base-T Crossed cable (PC to PC or HUB to HUB)

Crossed cables are used to connect PCs to one other PC or to connect a HUB to a HUB. Crossed cable are sometimes called Crossover, Patch or Jumper cables. If your connection is PC to HUB you MUST use a Straight cable.

The following description shows the wiring at both ends (male RJ45 connectors) of the crossed cable. Note: The diagrams below shows crossing of all 4 pairs and allows for the use of cat3/4 cables. Pairs 4,5 and 7,8 do not NEED to be crossed in 100base-TX wiring. See notes below.

NOTES:

1. All our crossed wiring is now done to the 100base-T4 spec which you can use with 10base-T networks - but NOT necessarily the other way around.
2. Most commercial cables these days seem not to cross pairs 4,5 and 7,8. If there is no cat3/4 wiring in the network this perfectly acceptable.
3. Gigabit Ethernet uses all 4 pairs so requires the full 4 pair (8 conductor) cross configuration (shown above).
4. If you are using Power-over-Ethernet (802.3af) then Mode A or Alternative A uses pairs 1,2 and 3,6 for both signals and power. Mode B or alternative B uses 4,5 and 7,8 to carry power. In all cases the spec calls for polarity insensitive implementation (using a diode bridge) and therefore crossing or not crossing pairs 4,5 and 7,8 will have no effect.

RJ45 Connector Pin Numbering

NOTES:

1. The RJ45 connector is the critical connection always use the highest quality connectors you can afford. The most common cause of connection faults is bad connectors. There are different connectors for stranded and solid cable. Sometimes you have to work quite hard to make sure you are getting the right type. Spend the time to make sure you have the right connector type. If you use the wrong type of connector the cable may or may not work initially but it will almost certainly fail very quickly.
2. Make and test practice cables until you get it right every time - especially before you destroy a cable you just spend 2 hours fitting.
3. When cutting the exterior cover of the cable be very careful not to cut the insulation cover of the conductors since this can cause shorts - bottom line: the cable won't work.
4. Expose a maximum of 1 inch of individual conductors when preparing the cable for connection.
5. Line up all the conductors according to the wiring standard you are using.
6. Measure the cable and trim the conductor ends so they are are all the same length and no individual conductor wire is visible outside the plastic cover of the RJ45 connector.
7. Carefully slide the prepared cable into the RJ45 connector making sure the end of the conductors reaches the end of the RJ45 connector.
8. Using the crimp tool make the connection using one firm squeeze operation.
9. Test the cable before fitting if possible.