How to wire your own ethernet cables and connectors.
What You Need:
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
About the Cable:
You can find bulk supplies of ethernet cable at many computer stores or most
electrical 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 for
gigabit (1000BaseT) operation and Cat 6 or higher gives you a measure of future
proofing. 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 in
patch applications for desktop use.
It is more flexible and resilient than solid ethernet cable and easier to work
with, 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 through
an air circulation space. For example, above a false ceiling or below a raised
floor. It may be difficult or
impossible to tell from the package or labeling what type of ethernet cable it is, so peal out an
end 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 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
ethernet cables won’t have any color on the striped wire, the only
way to tell which is which is to check which 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 ethernet cable. The TIA/EIA-568-A specifies two wiring
standards for an 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 consistency. I’ve shown both below for straight
through 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 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 sharp pointed contacts that actually pierce the wire. For solid wires, the connector has fingers which cut through 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 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 mounting
options. The choice is one of requirements and preference. Jacks are
designed to work only with solid ethernet cable. Most jacks come labeled with color
coded 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 straight
through ethernet cable, which is used to connect to a hub or switch, and a
crossover ethernet cable used to operate in a peer-to-peer fashion
without a hub/switch. Generally all fixed wiring should be run as straight
through. Some ethernet interfaces can cross
and un-cross a cable automatically as needed, a handy feature.
Standard, Straight-Through Wiring Diagram(both ends are the same):
RJ45 Pin #
Straight-Through Ethernet Cable Pin Out for T568A
RJ45 Pin #
Straight-Through Ethernet Cable Pin Out for T568B
Crossover Cable Wiring Diagram:
RJ45 Pin # (END 1)
Diagram End #1
RJ45 Pin # (END 2)
Diagram End #2
Crossover Ethernet Cable Pin Outs
+Note: The crossover ethernet cable layout is suitable for 1000Base-T
operation, 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 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 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 wire
is 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″ and
will 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 extend
to the front of the RJ45 plug and make good contact with the metal
contacts in the RJ45 plug
Cut the ethernet cable to length – make sure
it 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 to
At one end, cut the wire to length leaving enough length to work, but not too much
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 closely
at each end and see if you can find the problem. Often a
wire ended up in the wrong place or one of the wires is making no contact or
poor 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 end
connection should not extend more than 100m (~328ft).
Try to minimize the ethernet cable length, the
longer the cable becomes, the more it may affect performance. This is usually
noticeable as a gradual decrease in speed and increase in latency.
Power over Ethernet (PoE):
Power over Ethernet has been implemented in many variations before IEEE standardized 802.3af. IEEE 802.3af specifies the
ability 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 either
the 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 ethernet
configuration, including 10Base-T, 100Base-TX or 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 and supplies the power. No special cabling is
RJ45 Pin #
Mode A +
Mode A –
Mode B +
Mode B –
Power over Ethernet Power Delivery
EncodingSymbol Rate (Mbaud)Data EncodingData Bits per SymbolPairs per ChannelPairs UsedNyquist Frequency Bandwidth (MHz)Minimum Cable Category
1000Base-TIEEE 802.3ab4D-PAM5125None24462.55e (5)1
5GBase-TIEEE 802.3bzDSQ128 (2D-PAM16)400LDPC(1723,2048), 64B/65B, CRC83.125442006 (5e)2
25GBase-TIEEE 802.3bqDSQ128 (2D-PAM16)2000LDPC(1723,2048), 64B/65B, CRC83.12544100084
Data Rate=Symbol Rate x Data Bits per Symbol x Pairs per Channel
The combination of the Symbol Encoding and Data Encoding determines how
many Data Bits per Symbol there are.
1. Designed to work on most Cat 5 ethernet cable, Cat 5e specifications
ensure 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 CategoryRated Nyquist Frequency
Bandwidth (MHz)Common Uses
316Telephone Wiring, 10Base-T
Increasing category levels are backward compatible.
Manufacturers will often test and certify their ethernet cable well beyond the
1. Category 7/7a specification wiring does not use RJ45 connectors.
Related Reading Material
Get IEEE 802 – Ethernet Standards
Charles Spurgeon’s Ethernet Website
Network Connection Speeds Reference
Fiber Optic Connector Reference
The Definitive Guide
All-New Switch Book: The Complete Guide to LAN Switching
Technology times, since inception on September 1, 1997
Last Changed: January 31, 2019
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