How to wire Ethernet Cables (2024)

How to wire your own ethernet cables and connectors.

What You Need:

Required:

Ethernet Cable - bulk Category (Cat) 5, 5e, 6, 6a or higher ethernet cable
Wire Cutters - to cut and strip the ethernet cable if necessary
For Patch Cables:
- 8P8C Modular Connector Plugs ("RJ45")
- Modular Connector Crimper ("RJ45")
For Fixed Wiring:
- 8P8C Modular Connector Jacks ("RJ45")
- 110 Punch Down Tool

Recommended:

Wire Stripper
Cable Tester

About the Cable:

You can find bulk supplies of ethernet cable at many computer stores or mostelectrical or home centers. You want UTP (Unshielded Twisted Pair)ethernet cable of at least Category 5 (Cat 5). Cat 5 is required for basic 10/100 functionality, you will want Cat 5e forgigabit (1000BaseT) operation and Cat 6 or higher gives you a measure of futureproofing. You can also use STP (Shielded Twisted Pair) for extra resistance to external interference but I won't cover shielded connectors. Bulk ethernet cable comes in many types, there are 2 basic categories,solid and braided stranded cable. Stranded ethernet cable tends to work better inpatch applications for desktop use.It is more flexible and resilient than solid ethernet cable and easier to workwith, but really meant for shorter lengths.Solid ethernet cable is meant for longer runs in a fixed position.Plenum rated ethernet cable must be used whenever the cable travels throughan air circulation space. For example, above a false ceiling or below a raisedfloor. It may be difficult orimpossible to tell from the package or labeling what type of ethernet cable it is, so peal out anend and investigate.

Here is what the internals of the ethernet cable look like:

Internal Cable Structure and Color Coding

Inside the ethernet cable, there are 8 color coded wires. These wires are twistedinto 4 pairsof wires, each pair has a common color theme. One wire in the pair beinga solid or primarily solid colored wire and the other beinga primarily white wire with a colored stripe (Sometimesethernet cables won't have any color on the striped wire, the onlyway to tell which is which is to check which wire it is twisted around). Examplesof the naming schemes used are: Orange (alternatively Orange/White) forthe solid colored wire and White/Orange for the striped cable.The twists are extremely important. They are there to counteractnoise and interference. It is important to wire according to a standardto get proper performance from the ethernet cable. The TIA/EIA-568-A specifies two wiringstandards for an 8-position modular connector such as RJ45. The two wiringstandards, T568A and T568B varyonly in the arrangement of the colored pairs. Tom writes to say "...sourcessuggest using T568A cabling since T568B is theAT&T standard, but the US Government specifies T568A since it matches USOCcabling 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 orpersonal preference, but you should maintain consistency. I've shown both below for straightthrough cabling and just T568B for crossover cabling.

About Modular Connector Plugs and Jacks:

The 8P8C modular connectors for Ethernet are often called RJ45 due to their physical resemblance. The plug is an 8-position modular connector that looks like a largephone plug. There are a couple variations available.The primary variation you need to pay attention to is whether theconnector is intended for braided or solid wire.For braided/stranded wires, the connector has sharp pointed contacts that actually pierce the wire. For solid wires, the connector has fingers which cut through theinsulation and make contact with the wire by grasping it from both sides.The connector is the weak point in an ethernet cable, choosing the wrongone will often cause grief later. If you just walk into a computer store, it's nearly impossible to tell what type of plug it is. You may be able to determine what type it is by crimping one without a cable.

Modular connector jacks come in a variety styles intended for several different mountingoptions. The choice is one of requirements and preference. Jacks aredesigned to work only with solid ethernet cable. Most jacks come labeled with colorcoded wiring diagrams for either T568A, T568B or both. Make sure you end up with the correct one.

Here is a wiring diagram and pin out:

Modular Connector Plug and Jack Pin Out

Ethernet Cable Pin Outs:

There are two basic ethernet cable pin outs. A straightthrough ethernet cable, which is used to connect to a hub or switch, and acrossover ethernet cable used to operate in a peer-to-peer fashionwithout a hub/switch. Generally all fixed wiring should be run as straightthrough. Some ethernet interfaces can crossand un-cross a cable automatically as needed, a handy feature.

Standard, Straight-Through Wiring Diagram(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 Ethernet Cable Pin Out 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 Ethernet Cable Pin Out for T568B

Crossover Cable Wiring Diagram:

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

Crossover Ethernet Cable Pin Outs

+Note: The crossover ethernet cable layout is suitable for 1000Base-Toperation, all 4 pairs are crossed.

How to wire Ethernet Patch Cables:

Strip off about 2 inches of the ethernet cable sheath.
Untwist the pairs - don't untwist thembeyond what you have exposed, the more untwisted cable you have the worsethe problems you can run into.
Align the colored wires according to the wiring 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 plug - make sure each wireis fully inserted to the front of the RJ45 plug and in the correct order.The sheath of the ethernet cable should extend into the plug by about 1/2" andwill be held in place by the crimp.
Crimp the RJ45 plug with the crimper tool.
Verify the wires ended up the right order and that the wires extendto the front of the RJ45 plug and make good contact with the metalcontacts in the RJ45 plug
Cut the ethernet cable to length - make sureit is more than long enough for your needs.
Repeat the above steps for the second RJ45 plug.

How to wire fixed Ethernet Cables:

Run the full length of ethernet cable in place, from endpoint to endpoint, making sure toleave excess.
At one end, cut the wire to length leaving enough length to work, but not too muchexcess.
Strip off about 2 inches of the ethernet cable sheath.
Align each of the colored wires according to the layout of the jack.
Use the punch down tool to insert each wire into the jack.
Repeat the above steps for the second RJ45 jack.

If an ethernet cable tester is available, use it to verify the proper connectivity of the cable.That should be it, if your ethernet cable doesn't turn out, look closelyat each end and see if you can find the problem. Often awire ended up in the wrong place or one of the wires is making no contact orpoor contact. Also double check the color coding to verify it is correct. If you see a mistake or problem, cut the end off and start again. A ethernet cable tester is invaluable at identifying and highlighting these issues.

When sizing ethernet cables remember that an end to endconnection should not extend more than 100m (~328ft).Try to minimize the ethernet cable length, thelonger the cable becomes, the more it may affect performance. This is usuallynoticeable as a gradual decrease in speed and increase in latency.

Notes:

Power over Ethernet (PoE):

Power over Ethernet has been implemented in many variations before IEEE standardized 802.3af. IEEE 802.3af specifies theability to supply an endpoint device with 48V DC at up 350mA or approximately 16.8W. IEEE 802.3at updates the PoE standard to supply up to 600mA or approximately 28.8W, it is often known as PoE+. The power is delivered using two pairs in the ethernet cable. The device must be capable of receiving power on eitherthe data pairs [Mode A] (often called phantom power) or the unused pairs in 100Base-TX [Mode B]. IEEE 802.3bt further updates the PoE standard to use all four pairs of the cable to deliver up to 90W of power. PoE can be used with any ethernetconfiguration, including 10Base-T, 100Base-TX or 1000Base-T. Power is only supplied when a valid PoE endpoint isdetected by using a low voltage probe to look for the PoE signature on the endpoint. PoE power is typically suppliedin one of two ways, either the host ethernet switch provides the power, or a "midspan" device is plugged in betweenthe switch and endpoints and supplies the power. No special cabling isrequired.

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:

Protocol	Standard	SymbolEncoding	Symbol Rate (Mbaud)	Data Encoding	Data Bits per Symbol	Pairs per Channel	Pairs Used	Nyquist Frequency Bandwidth (MHz)	Minimum Cable Category
10Base-T	IEEE 802.3i	Manchester	10	None	1	1	2	10	3
100Base-TX	IEEE 802.3u	MLT-3	125	4B5B	4/5	1	2	62.5	5
1000Base-T	IEEE 802.3ab	4D-PAM5	125	None	2	4	4	62.5	5e (5)¹
2.5GBase-T	IEEE 802.3bz	DSQ128 (2D-PAM16)	200	LDPC(1723,2048), 64B/65B, CRC8	3.125	4	4	100	5e²
5GBase-T	IEEE 802.3bz	DSQ128 (2D-PAM16)	400	LDPC(1723,2048), 64B/65B, CRC8	3.125	4	4	200	6 (5e)²
10GBase-T	IEEE 802.3an	DSQ128 (2D-PAM16)	800	LDPC(1723,2048), 64B/65B, CRC8	3.125	4	4	400	6a (6)³
25GBase-T	IEEE 802.3bq	DSQ128 (2D-PAM16)	2000	LDPC(1723,2048), 64B/65B, CRC8	3.125	4	4	1000	8⁴
40GBase-T	IEEE 802.3bq	DSQ128 (2D-PAM16)	3200	LDPC(1723,2048), 64B/65B, CRC8	3.125	4	4	1600	8⁴

Data Rate = Symbol Rate x Data Bits per Symbol x Pairs per Channel
The combination of the Symbol Encoding and Data Encoding determines howmany Data Bits per Symbol there are.
1. Designed to work on most Cat 5 ethernet cable, Cat 5e specificationsensure 1000Base-T operation.
2. Although designed for Cat 5e/6, not all cabling will be usable at the full range, especially for 5GBase-T on Cat 5e.
3. Reduced range when used with Cat 6 (55m), Cat 6a supports the full 100m range. Some Cat 5e may support operation at reduced distance.
4. 30m range.

Cable Category Details:

Cable Category	Rated Nyquist FrequencyBandwidth (MHz)	Common Uses
1	None	Telephone Wiring
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
7¹	600	>10GBase-T
7a¹	1000	>10GBase-T
8	2000	25GBase-T, 40GBase-T

Increasing category levels are backward compatible.
Manufacturers will often test and certify their ethernet cable well beyond thestandards.
1. Category 7/7a specification wiring does not use RJ45 connectors.