How to wire Ethernet Cables

How to wire your own ethernet cables and connectors.

What You Need:

Required:

CAT 5 Cable - bulk Category 5, 5e or 6 cable
RJ45 Ends
Crimper for RJ45
Wire Cutters - to cut and strip the cable if necessary

Recommend:

Wire Stripper
Cable Tester

About the Cable:

You can find bulk supplies of the cable at many computer stores or most electrical or home centers. You want UTP (Unshielded Twisted Pair) Category 5 cable for basic 10/100 functionality. You need CAT 5e for gigabit (1000BaseT) operation and CAT 6 gives you a measure of future proofing. Bulk cable comes in many types, there are 2 basic categories, solid and braided cable. Braided cable tends to work better in "patch" applications for desktop use. It is more flexible and resiliant than solid cable and easier to work with, but really meant for shorter lengths. Solid cable is meant for longer runs in a fixed position. Plenum rated cable should/must be used whenever the cable travels through an air circulation space. For example, above a false celing or below a raised floor.

You're likely going to want braided type cable but it may be difficult or impossible to tell from the box.

Here is what the internals of the cable look like:

cat 5 cable
Internal Cable Structure and Color Coding

Inside the cable, there are 8 color coded wires. These wires are twisted into 4 pairs of wires, each pair has a common color theme. One wire in the pair being a solid or primarily solid colored wire and the other being a primarily white wire with a colored stripe (Sometimes cable doesn't have any color on the striped cable, the only way to tell is to check which other wire it is twisted around). Examples of the naming schemes used are: Orange (alternatively Orange/White) for the solid colored wire and White/Orange for the striped cable. The twists are extremely important. They are there to counteract noise and interference. It is important to wire according to a standard to get proper performance from the cable. The TIA/EIA-568-A specifies two wiring standards for a 8-position modular connector such as RJ45. The two wiring standards, T568A and T568B vary only in the arrangement of the colored pairs. Tom writes to say "...sources suggest using T568A cabling since T568B is the AT&T standard, but the US Government specifies T568A since it matches USOC cabling for pairs 1 & 2, which allows it to work for 1/2 line phones...". Your choice might be determined by the need to match existing wiring, jacks or personal preference, but you should maintain consistancy. I've shown both below for straight through cabling and just T568B for cross over cabling.

About the RJ45 Ends:

The RJ45 end is a 8-position modular connector that looks like a large phone plug. There are a couple variations available. The primary variation you need to pay attention to is whether the connector is intended for braided or solid wire. For braided/stranded wires, the connector has contacts that actually pierce the wire. For solid wires, the connector has fingers which pierce the insulation and make contact with the wire by grasping it from both sides. The connector is the weak point in an ethernet cable, choosing the wrong one will often cause grief later. If you just walk into a computer store, it's nearly impossible to tell what type of connector it is.

Here is a diagram and pinout:

rj45 jack pinout
RJ45 Jack and Plug Pinout

Ethernet Cable Pinouts:

There are two basic cables. A straight through cable, which is used to connect to a hub or switch, and a cross over cable used to operate in a peer-to-peer fashion without a hub/switch. Some interfaces can cross and un-cross a cable automatically as needed, really quite nice.

Standard, Straight-Through Wiring (both ends are the same):

RJ45 Pin #	Wire Color (T568A)	10Base-T Signal 100Base-TX Signal	1000Base-T Signal
1	White/Green	Transmit+	BI_DA+
2	Green	Transmit-	BI_DA-
3	White/Orange	Receive+	BI_DB+
4	Blue	Unused	BI_DC+
5	White/Blue	Unused	BI_DC-
6	Orange	Receive-	BI_DB-
7	White/Brown	Unused	BI_DD+
8	Brown	Unused	BI_DD-

Straight-Through Cable Pinout for T568A

RJ45 Pin #	Wire Color (T568B)	10Base-T Signal 100Base-TX Signal	1000Base-T Signal
1	White/Orange	Transmit+	BI_DA+
2	Orange	Transmit-	BI_DA-
3	White/Green	Receive+	BI_DB+
4	Blue	Unused	BI_DC+
5	White/Blue	Unused	BI_DC-
6	Green	Receive-	BI_DB-
7	White/Brown	Unused	BI_DD+
8	Brown	Unused	BI_DD-

Straight-Through Cable Pinout for T568B

Cross Over Cable (T568B):

RJ45 Pin # (END 1)	Wire Color	RJ45 Pin # (END 2)	Wire Color
1	White/Orange	1	White/Green
2	Orange	2	Green
3	White/Green	3	White/Orange
4	Blue	4	White/Brown
5	White/Blue	5	Brown
6	Green	6	Orange
7	White/Brown	7	Blue
8	Brown	8	White/Blue

Cross Over Cable Pinouts

+Note: The cross over cable layout is suitable for 1000Base-T operation, all 4 pairs are crossed.

How to wire Ethernet Cables:

Strip off about 2 inches of the cable sheath.
Untwist the pairs - don't untwist them beyond what you have exposed, the more untwisted cable you have the worse the problems you can run into.
Align the colored wires according to the diagrams above.
Trim all the wires to the same length, about 1/2" to 3/4" left exposed from the sheath.
Insert the wires into the RJ45 end - make sure each wire is fully inserted to the front of the RJ45 end and in the correct order. The sheath of the cable should extend into the RJ45 end by about 1/2" and will be held in place by the crimp.
Crimp the RJ45 end with the crimper tool
Verify the wires ended up the right order and that the wires extend to the front of the RJ45 end and make good contact with the metal contacts in the RJ45 end.
Cut the cable to length - make sure it is more than long enough for your needs. Remember, an end to end connection should not extend more than 100m (~328ft). Try to keep cables short, the longer the cable becomes the more it may affect performance, usually noticable as a gradual decrease in speed and increase in latency.
Repeat the above steps for the second RJ45 end.
If a cable tester is available, use it to verify the proper connectivity of the cable.

That should be it, if your cable doesn't turn out, look closely at each end and see if you can find the problem. Usually a wire ended up in the wrong place or more commonly, one of the wires didn't extend to the front of the RJ45 connector and is making no, or poor contact. If you see a mistake or problem, cut the end off and start again.

Notes:

Power over Ethernet (PoE):

Power over Ethernet has been implemented in many variations before IEEE standardized 802.3af. 802.3af specifies the ability to supply an endpoint with 48V DC at up 350mA or 16.8W. The endpoint must be capable of receiving power on either the data pairs [Mode A] (often called phantom power) or the unused pairs [Mode B] in 100Base-TX. PoE can be used with any ethernet configuration, including 10Base-T, 100Base-TX and 1000Base-T. Power is only supplied when a valid PoE endpoint is detected by using a low voltage probe to look for the PoE signature on the endpoint. PoE power is typically supplied in one of two ways, either the host ethernet switch provides the power, or a "midspan" device is plugged in between the switch and endpoints which supplies the power. No special cabling is required.

RJ45 Pin #	Wire Color (T568A)	10Base-T Signal 100Base-TX Signal	PoE
1	White/Green	Transmit+	Mode A +
2	Green	Transmit-	Mode A +
3	White/Orange	Receive+	Mode A -
4	Blue	Unused	Mode B +
5	White/Blue	Unused	Mode B +
6	Orange	Receive-	Mode A -
7	White/Brown	Unused	Mode B -
8	Brown	Unused	Mode B -

Power over Ethernet Power Delivery

Protocol Details:

	Frequency (MHz)	Symbol Encoding	Signal Rate (Mbaud)	Symbol Rate	Data Encoding	Data Bits per Symbol	Pairs per Channel	Pairs Used	Minimum Cable Category
10BaseT	10	Manchester	10	10	None	1	1	2	3
100BaseT4	12.5	Multi-level, 2T/Hz	25	25	8B6T	8/6	3	4	3
100BaseTX	31.25	MLT-3	125	125	4B5B	4/5	1	2	5
100BaseT2	12.5	PAM5x5 (2D-PAM5)	25	12.5	None	4 (2x2)	2	2	3
1000BaseT	31.25	4D-PAM5	125	31.25	None	8 (4x2)	4	4	5*

*Designed to work on MOST category 5 cable, category 5e specifications ensure 1000Base-T operation

Cable Category Details:

Cable Category	Rated Frequency Bandwidth (MHz)	Common Uses
1	None	Common Use
2	1	Telephone Wiring
3	16	Telephone Wiring, 10Base-T
4	20	Token-Ring, 10Base-T
5	100	100Base-TX, 10Base-T
5e	100	1000Base-T, 100Base-TX
6	250	1000Base-T, 100Base-TX
6a*	500	10GBase-T
7	600

Increasing category levels are backward compatible.
Manufacturers will often test and certify their cable well beyond the standards.
*10GBase-T should work on Cat6, but to get the full 100m range, Cat 6a is required.