Power over Ethernet (PoE) is a technology that allows electrical DC power and Ethernet data to travel over the same twisted-pair network cable. A single Ethernet cable can therefore provide both network connectivity and operating power to devices such as IP cameras, wireless access points, VoIP telephones and many other network-connected devices.

A normal Ethernet cable contains four twisted pairs, giving a total of eight copper conductors. The familiar T568B color code determines which colored conductor is connected to pins 1 through 8 of an RJ45/8P8C connector.

An important point is:

There is no separate "PoE color code." PoE uses the same standard T568A or T568B Ethernet wiring. The PoE equipment determines which electrical pairs carry power.

This distinction is important because technicians sometimes assume that blue and brown wires are always "PoE wires." That is only true for certain PoE arrangements, particularly Alternative/Mode B in 10/100 Mbps Ethernet. Standards-based PoE may also place power on the orange and green data pairs, and IEEE 802.3bt may use all four pairs.

T568B RJ45 Color Code

When looking at an RJ45 plug with the gold contacts facing you and the locking tab facing away/downward, pins are normally counted from left to right, 1 through 8.

The standard T568B conductor sequence is:

Pin	T568B Wire Color	Twisted Pair	Traditional 10/100 Mbps Function
1	White/Orange	Orange Pair	Data
2	Orange	Orange Pair	Data
3	White/Green	Green Pair	Data
4	Blue	Blue Pair	Spare in 10/100
5	White/Blue	Blue Pair	Spare in 10/100
6	Green	Green Pair	Data
7	White/Brown	Brown Pair	Spare in 10/100
8	Brown	Brown Pair	Spare in 10/100

This T568B mapping is widely used for Ethernet structured cabling.

A convenient way to remember the order is:

White/Orange – Orange – White/Green – Blue – White/Blue – Green – White/Brown – Brown

or:

WO – O – WG – B – WB – G – WBr – Br

Understanding the Four Twisted Pairs

T568B contains four physical twisted pairs.

Pair	Colors	Pins
Orange Pair	White/Orange + Orange	1 and 2
Green Pair	White/Green + Green	3 and 6
Blue Pair	Blue + White/Blue	4 and 5
Brown Pair	White/Brown + Brown	7 and 8

Notice something unusual:

The green pair does not appear on adjacent pins.

It uses:

Pin 3 = White/Green

and

Pin 6 = Green

This is intentional and is part of the Ethernet pin assignment.

Which T568B Colors Carry PoE Power?

The answer depends on the PoE operating method.

There are three important configurations to understand:

Mode/Alternative A

Mode/Alternative B

4-pair PoE / 4PPoE

IEEE-standard PoE supports these powering concepts, with modern 802.3bt systems capable of using all four pairs.

PoE Mode A / Alternative A

In Mode A, power is carried over the same conductor pairs used for data in 10BASE-T and 100BASE-TX.

For T568B these are:

Pins	T568B Colors	Function
1 & 2	White/Orange + Orange	Data + PoE
3 & 6	White/Green + Green	Data + PoE

Therefore, in Mode A the PoE power travels through:

White/Orange

Orange

White/Green

Green

Mode A uses a technique commonly described as phantom powering, where DC is applied in common mode through transformer center taps while Ethernet differential data remains on the same twisted pairs.

This means data and DC electrical power can coexist on the same physical conductors.

Why Doesn't PoE Power Interfere with Ethernet Data?

Ethernet data is transmitted as differential electrical signaling between the two wires in a twisted pair.

PoE DC power is applied differently, effectively placing a similar DC potential on both wires of a pair relative to another pair.

Because the data transceiver works with the difference between conductors, while PoE is coupled through Ethernet magnetics, the power and data can coexist.

This transformer/center-tap arrangement is one of the key technologies that makes standards-based PoE possible.

PoE Mode B / Alternative B

In Mode B, traditional 10/100 Mbps Ethernet uses one set of pairs for data and another set for power.

The power conductors are:

Pins	T568B Colors	Mode B Function
4 & 5	Blue + White/Blue	PoE power side
7 & 8	White/Brown + Brown	PoE return side

Therefore, when technicians refer to the "PoE wires" as:

Blue

White/Blue

White/Brown

Brown

they are generally referring specifically to Mode B / Alternative B operation on 10/100 Mbps Ethernet.

In this arrangement, pins 1, 2, 3 and 6 traditionally carry Ethernet data, while pins 4, 5, 7 and 8 carry electrical power.

Simple T568B PoE Mode B Diagram

RJ45 T568B

Pin 1  White/Orange   Data
Pin 2  Orange         Data
Pin 3  White/Green    Data

Pin 4  Blue           PoE
Pin 5  White/Blue     PoE

Pin 6  Green          Data

Pin 7  White/Brown    PoE
Pin 8  Brown          PoE

This representation is useful for understanding older 10/100 Mbps PoE installations, but it should not be interpreted as a universal rule for every PoE implementation.

Mode A vs Mode B

Feature	Mode A / Alternative A	Mode B / Alternative B
Pins carrying power	1, 2, 3, 6	4, 5, 7, 8
T568B colors	Orange + Green pairs	Blue + Brown pairs
10/100 data pairs	Same as power	Separate from power
Power technique	Phantom power	Traditionally spare-pair power
Common terminology	End-span style powering	Mid-span/spare-pair style powering
Compatible PD expectation	Standards-compliant PD should accommodate permitted powering alternatives	Standards-compliant PD should accommodate permitted powering alternatives

IEEE PoE specifies how PSE and PD equipment detect and supply power rather than requiring installers to create a special Ethernet cable.

What Happens with Gigabit Ethernet?

This is where the idea of "unused wires" becomes misleading.

1000BASE-T Gigabit Ethernet uses all four twisted pairs for data.

Therefore:

Pins 1–2 carry data.

Pins 3–6 carry data.

Pins 4–5 carry data.

Pins 7–8 carry data.

There are no unused pairs available in the traditional sense.

PoE can still operate because electrical power is superimposed through the Ethernet magnetics while the same conductors carry network data.

So on Gigabit Ethernet:

Blue and brown wires may carry both data and electrical power.

What Is 4-Pair PoE / 4PPoE?

Modern higher-power PoE defined by IEEE 802.3bt can use all four twisted pairs for electrical power.

That means:

Pair 1: Pins 1–2

Pair 2: Pins 3–6

Pair 3: Pins 4–5

Pair 4: Pins 7–8

may all participate in power delivery.

IEEE 802.3bt introduced Type 3 and Type 4 operation and extended PoE capability to as much as 60 W or 90 W at the PSE, depending on the implementation.

PoE Standards and Power Levels

The major standards are:

PoE Type	IEEE Standard	Common Name	PSE Maximum	Approx. Maximum Available to PD
Type 1	IEEE 802.3af	PoE	15.4 W	12.95 W
Type 2	IEEE 802.3at	PoE+	30 W	25.5 W
Type 3	IEEE 802.3bt	PoE++ / 4PPoE	60 W	51 W
Type 4	IEEE 802.3bt	PoE++ / 4PPoE	90 W	approximately 71 W

Cisco's IEEE 802.3bt technical documentation gives corresponding maximum PSE values of 15.4 W, 30 W, 60 W and 90 W, with maximum PD values of approximately 12.95 W, 25.5 W, 51 W and 71 W respectively.

The difference between PSE output and PD input exists largely because some power is lost in the cable and connection system.

What Are PSE and PD?

Two abbreviations are extremely important when working with PoE.

PSE – Power Sourcing Equipment

The PSE supplies the electrical power.

Examples include:

PoE network switches

PoE injectors

PoE-enabled industrial switches

Midspan PoE equipment

Cisco describes the PoE-capable switch port as providing power from its PSE to the connected powered device.

PD – Powered Device

The PD receives and consumes PoE power.

Typical examples include:

IP cameras

VoIP phones

wireless access points

video intercom systems

door access controllers

IoT gateways

PoE speakers

thin clients

small network switches

Active PoE Detection

Standards-based PoE is much safer than simply applying voltage directly to arbitrary Ethernet conductors.

A normal IEEE-compatible PSE does not simply connect full operating power immediately.

The general sequence includes:

Detection

Classification

Power application

Power maintenance/monitoring

The PSE first determines whether a compatible powered device is attached before supplying normal PoE power. IEEE PoE includes powered-device discovery and power classification mechanisms.

This is one of the reasons standards-based PoE switches can normally be connected to non-PoE Ethernet devices safely.

What Is Passive PoE?

Passive PoE is not the same thing as normal IEEE standards-based PoE.

Some passive injectors simply place a fixed DC voltage onto selected Ethernet conductors without IEEE detection or power negotiation.

Depending on the equipment, passive PoE may use voltages such as 12 V, 24 V or 48 V and may have manufacturer-specific pin assignments.

This can be dangerous because connecting an incompatible passive PoE source to equipment may damage the connected device.

Therefore:

Never assume that a device marked "PoE" uses IEEE 802.3af/at/bt.

Check the manufacturer's specification.

Look specifically for:

IEEE 802.3af

IEEE 802.3at

or

IEEE 802.3bt

Does T568B Decide PoE Polarity?

Not by itself.

T568B determines which wire color goes to which RJ45 pin.

The PoE standard and PSE circuitry determine how power is presented across the pairsets.

For example, Mode B uses pins 4–5 as one power pairset and 7–8 as the other. Mode A instead uses the pairsets associated with pins 1–2 and 3–6.

Therefore it is better to discuss PoE electrically using pin numbers and pairsets, rather than relying only on wire colors.

T568A vs T568B and PoE

PoE works with both T568A and T568B structured cabling.

The main difference between T568A and T568B is that the orange and green pairs exchange positions.

The blue and brown pairs remain in the same locations.

For T568B:

1 White/Orange
2 Orange
3 White/Green
4 Blue
5 White/Blue
6 Green
7 White/Brown
8 Brown

For T568A:

1 White/Green
2 Green
3 White/Orange
4 Blue
5 White/Blue
6 Orange
7 White/Brown
8 Brown

The T568A/T568B conductor assignments are documented in common Ethernet cabling references.

PoE operation is based primarily on the correct pair/pin relationships, so either properly terminated standard can support PoE.

Should Both Ends Be T568B?

For a normal straight-through Ethernet cable, yes.

Terminate:

End A = T568B

and

End B = T568B

This creates a conventional straight-through patch cable.

For most modern LAN installations, consistency matters more than choosing A versus B. If an installation already follows T568B, maintain T568B throughout the patch panel, keystone jacks and patch leads unless there is a specific engineering requirement to do otherwise.

Correct T568B Crimping Order

Place the cable conductors in this order:

PIN 1  White/Orange
PIN 2  Orange
PIN 3  White/Green
PIN 4  Blue
PIN 5  White/Blue
PIN 6  Green
PIN 7  White/Brown
PIN 8  Brown

The critical requirement is not merely matching colors from end to end.

The twisted-pair structure must also be preserved.

For example:

Pins 1 and 2 must remain one twisted pair.

Pins 3 and 6 must remain one twisted pair.

Pins 4 and 5 must remain one twisted pair.

Pins 7 and 8 must remain one twisted pair.

A cable that electrically maps pin 1 to pin 1, pin 2 to pin 2 and so on can still perform badly if the technician separates conductors from their proper twisted pairs. Such a mistake is commonly called a split pair.

Why Twisted Pairs Matter for PoE

Twisting provides several important electrical advantages:

Reduced electromagnetic interference

Reduced crosstalk

Improved balanced data signaling

More predictable conductor characteristics

Better high-frequency Ethernet performance

When PoE power is added, conductor quality and pair resistance become increasingly important because current flowing through resistance generates heat.

High-power PoE therefore makes proper cable quality, connector quality, bundle design and termination particularly important. Ethernet Alliance guidance specifically discusses cabling-system heating considerations for high-power IEEE 802.3bt installations.

Should You Use Copper or CCA Cable for PoE?

For professional PoE installations, solid copper Category-rated cable is strongly preferred.

CCA means Copper-Clad Aluminum.

CCA conductors generally have greater electrical resistance than equivalent copper conductors, making them undesirable for demanding PoE applications where current, voltage drop and heating matter.

For IP cameras, enterprise access points and higher-power PoE devices, use reputable standards-compliant copper cabling rather than selecting cable only because it is inexpensive.

For higher-power 802.3bt deployments, cable performance and thermal characteristics become especially important.

Recommended Cable Categories

Depending on network speed, installation design and PoE power requirements, common choices include:

Cat5e

Suitable for many standard Ethernet and PoE installations.

Cat6

Often preferred for modern new installations and Gigabit networks.

Cat6A

A strong choice for higher-performance structured cabling, 10 Gigabit Ethernet and demanding PoE deployments.

IEEE 802.3bt was designed for operation over suitable standards-compliant Ethernet cabling and uses four-pair powering for higher power levels.

Maximum Ethernet Cable Length

The commonly used Ethernet structured-cabling channel limit is approximately 100 metres, typically consisting of permanent horizontal cabling plus patch leads.

PoE also experiences voltage drop over distance because every copper conductor has resistance.

This means a powered device at the far end receives somewhat less power than the PSE produces, which is reflected in the distinction between PSE output power and maximum PD input power in IEEE PoE classes.

Example: PoE CCTV Camera on T568B

Imagine a PoE IP camera connected to an IEEE-compliant PoE switch using Cat6 cable terminated as T568B.

The cable wiring is:

1 White/Orange
2 Orange
3 White/Green
4 Blue
5 White/Blue
6 Green
7 White/Brown
8 Brown

You do not need to manually decide which conductor carries +48 V or return power.

The Ethernet cable should simply be wired correctly according to T568B at both ends.

The switch's PSE circuitry and the camera's PD circuitry handle IEEE PoE detection and power delivery.

That is one of the most important practical concepts for technicians to understand.

Example: PoE Wireless Access Point

Modern enterprise wireless access points commonly require more power than simple IP cameras.

Depending on the AP, it may require:

PoE

PoE+

or higher-power 802.3bt PoE.

Using a lower-power switch does not necessarily mean the AP will fail completely. Some enterprise APs may boot with restricted capabilities, disable radios, limit USB functionality or refuse to operate normally depending on their design.

Therefore, always verify the device's required PoE standard and power class, not merely whether the switch displays the word "PoE."

PoE Power Budget

A PoE switch may have 8, 16, 24 or 48 PoE-capable ports, but this does not automatically mean that every port can simultaneously supply maximum power.

PoE switches have a power budget.

For example, a 24-port switch may technically support PoE+ on every port but have a total available PoE budget lower than:

24 × 30 W = 720 W

Therefore technicians must check:

number of powered devices

power requirement of each PD

PoE class

total switch PoE budget

available switch power supply capacity

Cisco documentation notes that the switch tracks available PoE power and allocates power based on available budget and connected devices.

Why an Ordinary Cable Tester Is Not Enough

A basic RJ45 continuity tester generally tells you whether:

Pin 1 reaches pin 1

Pin 2 reaches pin 2

and so on.

It may detect:

open circuits

short circuits

reversed conductors

crossed conductors

But a simple tester may not tell you:

actual PoE voltage

PoE standard

power class

pairset supplying power

available wattage

load performance

voltage drop under load

For PoE troubleshooting, a dedicated PoE tester/analyzer is considerably more useful.

How to Test a PoE Network

A good PoE diagnostic procedure should verify:

1. RJ45 pin continuity.
2. T568B termination sequence.
3. Correct pair structure.
4. Cable category.
5. Cable length.
6. Whether the PSE detects the PD.
7. PoE voltage.
8. PoE standard/class.
9. Switch power budget.
10. Power consumption of the connected device.
11. Connector quality.
12. Excessive cable heating or resistance.
13. Patch-panel and keystone termination.
14. Whether passive or active PoE equipment is involved.
15. Whether the powered device requires more power than the PSE can provide.

Common PoE Wiring Mistakes

1. Assuming only blue and brown wires carry power

This assumption only applies to certain Mode B arrangements.

Mode A can use orange and green pairsets, while modern four-pair PoE can use all four pairs.

2. Wiring only four conductors

A four-wire cable may operate with certain legacy 10/100 Mbps arrangements but should not be treated as proper modern structured cabling.

Gigabit Ethernet uses all four twisted pairs.

Modern PoE and especially 802.3bt deployments should use correctly terminated eight-conductor cable.

3. Mixing T568A and T568B accidentally

If one side is T568A and the other side is T568B, the cable becomes a crossover configuration rather than a normal straight-through cable.

Modern Ethernet equipment may compensate using Auto-MDI/MDIX, but deliberate, consistent termination is better practice.

4. Using poor-quality RJ45 connectors

Bad connectors can increase resistance, cause intermittent connectivity and contribute to heating under PoE load.

5. Excessively untwisting pairs

Keep each twisted pair twisted as close to the connector termination as practical.

6. Using low-quality cable for high-current PoE

Higher-power PoE increases the importance of conductor resistance and cable-bundle temperature.

7. Connecting passive PoE blindly

Never connect an unknown passive injector merely because the connector is RJ45.

Verify voltage, polarity and pin assignment first.

Quick Technical Reference

T568B

1  White/Orange
2  Orange
3  White/Green
4  Blue
5  White/Blue
6  Green
7  White/Brown
8  Brown

Mode A

Power pairsets:
Pins 1-2
Pins 3-6

T568B colors:
White/Orange + Orange
White/Green + Green

Mode B

Power pairsets:
Pins 4-5
Pins 7-8

T568B colors:
Blue + White/Blue
White/Brown + Brown

4-Pair PoE / IEEE 802.3bt

Power can use all four pairsets:

1-2
3-6
4-5
7-8

These pair assignments correspond to the standard PoE powering alternatives and four-pair operation.

Important Safety Note

Although PoE voltage is considerably lower than household mains voltage, it is still electrical power.

Care should be taken when:

terminating live PoE cabling

working with damaged connectors

handling high-power 802.3bt installations

installing large cable bundles

using passive PoE injectors

working around wet environments

testing unidentified network cabling

Whenever possible, disconnect or disable PoE on the relevant switch port before reterminating a connector.

Higher-power PoE installations deserve particular attention to cable quality, connection resistance and heat accumulation in large bundles.

Frequently Asked Questions – FAQ

1. What is the T568B color code?

The T568B RJ45 wiring sequence is:

White/Orange, Orange, White/Green, Blue, White/Blue, Green, White/Brown, Brown.

2. Which color wires carry PoE?

There is no single universal PoE color pair.

In T568B:

Mode A: orange and green pairs.

Mode B: blue and brown pairs.

4-pair PoE: all four pairs may carry power.

3. Which pins are used for PoE Mode A?

Mode A uses:

Pins 1, 2, 3 and 6.

4. Which pins are used for PoE Mode B?

Mode B uses:

Pins 4, 5, 7 and 8.

5. What colors are pins 4, 5, 7 and 8 in T568B?

They are:

Pin 4 = Blue

Pin 5 = White/Blue

Pin 7 = White/Brown

Pin 8 = Brown.

6. Are pins 4, 5, 7 and 8 always unused for Ethernet data?

No.

They are traditionally unused for 10BASE-T and 100BASE-TX data, but Gigabit Ethernet uses all four twisted pairs.

7. Can Gigabit Ethernet and PoE work together?

Yes.

Gigabit Ethernet can simultaneously carry Ethernet data and PoE using the same four-pair cabling system.

8. Does PoE require a special Ethernet cable?

Normally no special pinout is required.

A properly terminated standards-compliant Ethernet cable such as Cat5e, Cat6 or Cat6A is typically used. Higher-power systems should use appropriate high-quality cabling suitable for the installation.

9. Should I wire a PoE cable differently from a normal Ethernet cable?

No.

For standards-based PoE, terminate the Ethernet cable normally according to T568A or T568B.

The PSE and PD electronics control the PoE operation.

10. Can I use T568A for PoE?

Yes.

Both T568A and T568B can support standards-based PoE when correctly terminated.

11. Is T568B better than T568A for PoE?

Not inherently.

PoE compatibility does not depend on choosing T568B instead of T568A. Consistent standards-compliant pair termination is what matters.

12. What is PoE+?

PoE+ refers to IEEE 802.3at Type 2, which supports up to approximately 30 W from the PSE.

13. What is PoE++?

PoE++ is commonly associated with IEEE 802.3bt, which enables higher power through four-pair powering.

Type 3 can provide up to approximately 60 W at the PSE, while Type 4 can provide up to approximately 90 W at the PSE.

14. What is 4PPoE?

4PPoE means Four-Pair Power over Ethernet.

Instead of supplying power through only two pairsets, all four twisted pairs participate in power delivery. IEEE 802.3bt introduced standardized four-pair powering for higher-power applications.

15. Can PoE damage a normal computer?

A properly functioning standards-compliant IEEE PoE PSE performs powered-device detection before normal power application, which greatly reduces the risk of applying PoE power to incompatible non-PoE equipment.

However, non-standard passive PoE equipment requires much greater caution.

16. What is phantom power in PoE?

Phantom powering allows DC power and Ethernet data to share twisted pairs by applying power through Ethernet magnetics in a way that does not interfere with differential data signaling. Mode A is a classic example.

17. Can I use a 4-wire Ethernet cable for PoE?

Certain legacy 10/100 arrangements may function using fewer conductors, but it is not recommended for modern structured network installations.

Use all eight correctly terminated conductors for reliable Gigabit Ethernet and modern PoE.

18. Why does my PoE camera work at 100 Mbps but not Gigabit?

Many IP cameras only contain a Fast Ethernet interface, so 100 Mbps may be completely normal.

If the camera is supposed to support Gigabit Ethernet, check all eight conductors because Gigabit Ethernet requires all four pairs.

19. Why does my PoE device power on but lose network connectivity?

Possible causes include:

incorrect T568B termination

split pairs

damaged conductor

poor RJ45 termination

excessive cable length

high cable resistance

bad patch panel connection

insufficient switch PoE budget

damaged Ethernet port

poor-quality cable

A cable and PoE analyzer can help differentiate power problems from data-layer problems.

20. Why does a PoE access point keep restarting?

Common possibilities include insufficient PoE power, excessive voltage drop, poor termination, high resistance, an undersized switch power budget, wrong PoE class or a defective cable/device.

Check both the Ethernet link and negotiated PoE power.

21. Can a PoE switch automatically identify the connected device?

IEEE-compliant PoE includes powered-device detection and classification mechanisms. The switch can determine whether a compatible PD is present before supplying normal operating power.

22. What is a PoE injector?

A PoE injector adds electrical power to an Ethernet connection when the upstream network switch does not provide PoE.

It is commonly used to power a single IP camera, access point or other PD.

23. What is a PoE splitter?

A PoE splitter receives PoE and separates it into:

Ethernet data

and

DC power

for equipment that requires separate Ethernet and DC connectors.

The splitter must match the connected device's required output voltage and power.

24. What is a PoE extender?

A PoE extender is used in specialized installations to extend Ethernet/PoE reach beyond a normal individual Ethernet segment by regenerating the network connection and forwarding available PoE power.

Actual supported distances and power depend on the extender and installation design.

25. Should technicians remember PoE by color or pin number?

Pin number and pairset are preferable.

Colors depend on T568A versus T568B, while PoE standards describe electrical operation in terms of pairs and connector pins.

For example:

Mode A = 1-2 and 3-6
Mode B = 4-5 and 7-8
4PPoE = all four pairsets

That approach avoids many cabling mistakes.

Final Technical Summary

For a T568B Ethernet cable, the standard conductor order is:

Pin 1 – White/Orange
Pin 2 – Orange
Pin 3 – White/Green
Pin 4 – Blue
Pin 5 – White/Blue
Pin 6 – Green
Pin 7 – White/Brown
Pin 8 – Brown

For Power over Ethernet:

PoE Mode A
Pins 1-2 + 3-6
Orange + Green pairs

PoE Mode B
Pins 4-5 + 7-8
Blue + Brown pairs

IEEE 802.3bt / 4PPoE
All four twisted pairs can carry power

The most important principle is:

Do not manufacture a special "PoE cable" by moving wires around. Terminate the cable correctly according to T568A or T568B and allow standards-compliant PSE and PD equipment to determine how power is supplied.

IEEE PoE has evolved from two-pair IEEE 802.3af and 802.3at operation to four-pair IEEE 802.3bt systems capable of substantially higher power delivery.

For professional installations, use high-quality copper Ethernet cable, correct pair termination, suitable connectors, an appropriate PoE switch or injector, and a PoE-aware cable tester—especially when deploying high-power wireless access points, surveillance systems or IEEE 802.3bt equipment.

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