What Are the 4 Wires for in a POE Camera Explained

POE cameras use four wires to deliver both power and data over a single Ethernet cable, simplifying installation and reducing clutter. Two pairs of wires handle data transmission (via Ethernet) and power delivery (via POE standards like 802.3af/at), ensuring seamless operation without separate power sources. This dual-purpose wiring makes POE cameras a reliable, cost-effective choice for modern surveillance systems.

Key Takeaways

• Power delivery: Two wires supply safe, efficient power to the camera.
• Data transmission: Two wires enable fast, reliable network communication.
• Simplified cabling: Combines power and data in one Ethernet cable.
• Standard compliance: Uses IEEE 802.3af/at for universal compatibility.
• Installation ease: Reduces wiring complexity and saves time.
• Scalability: Ideal for expanding surveillance systems with minimal effort.

Understanding the Basics of POE Cameras and Their Wiring

Power over Ethernet (PoE) cameras have revolutionized the world of surveillance by simplifying installation, reducing clutter, and improving system reliability. Unlike traditional analog or IP cameras that require separate power and data cables, PoE cameras draw both power and transmit data through a single Ethernet cable. This innovation not only cuts down on wiring complexity but also enables flexible camera placement in areas where power outlets are scarce or impractical. Whether you’re setting up a home security system or managing a large-scale commercial surveillance network, understanding the wiring behind PoE cameras is essential for optimal performance and troubleshooting.

At the heart of this technology lies the Ethernet cable—most commonly a Cat5e or Cat6 cable—which contains four twisted pairs of wires, totaling eight individual wires. However, when it comes to PoE cameras, only four of these eight wires are actively used in most standard implementations. This raises a critical question: What are the 4 wires for in a POE camera? The answer lies in the dual function of the Ethernet cable: transmitting data and delivering electrical power. In this article, we’ll dive deep into the roles of these four wires, how PoE standards utilize them, and why understanding this wiring is key to maximizing the efficiency and safety of your surveillance setup.

The Anatomy of an Ethernet Cable: Breaking Down the 8 Wires

How Ethernet Cables Are Constructed

Standard Ethernet cables used in PoE systems—such as Cat5e, Cat6, or Cat6a—are made up of four twisted pairs, each consisting of two insulated copper wires. These are color-coded for easy identification and termination. The pairs are:

• Orange and White-Orange (Pair 1)
• Green and White-Green (Pair 2)
• Blue and White-Blue (Pair 3)
• Brown and White-Brown (Pair 4)

Twisting the wires reduces electromagnetic interference (EMI) and crosstalk, ensuring high-speed, reliable data transmission. The cable is terminated using an RJ45 connector, which aligns the eight wires into specific pin positions based on wiring standards like T568A or T568B.

Which Wires Are Used in PoE Camera Systems?

For PoE cameras, only four of the eight wires are typically used: two for data and two for power. The exact configuration depends on the PoE standard being used (more on that later), but the most common setup involves:

• Data Transmission: Pins 1, 2, 3, and 6 (White-Orange, Orange, White-Green, Green)
• Power Delivery: Pins 1, 2, 3, and 6—or in some cases, Pins 4, 5, 7, and 8 (Blue, White-Blue, Brown, White-Brown)

It’s important to note that in 10/100 Mbps Ethernet (Fast Ethernet), only two of the four pairs are used for data—specifically, Pins 1–2 (Transmit) and Pins 3–6 (Receive). This leaves the other two pairs (Pins 4–5 and 7–8) available for power delivery. However, in 1000 Mbps (Gigabit Ethernet), all four pairs are used for data, meaning power must be delivered simultaneously over the same wires—a method known as Alternative A or Midspan power delivery.

Practical Example: Installing a PoE Camera with Cat5e

Imagine installing a PoE dome camera on the side of a warehouse. You run a 100-foot Cat5e cable from the network switch (which supports PoE) to the camera location. The installer follows the T568B standard and terminates both ends correctly. In this case:

• Data is sent and received via Pins 1–2 (Tx) and 3–6 (Rx)
• Power is delivered over Pins 4–5 (positive) and 7–8 (negative) — known as Alternative B

This setup ensures that data flows uninterrupted while 48V DC power powers the camera, eliminating the need for a nearby AC outlet.

How PoE Standards Determine Wire Usage

PoE Standards: A Brief Overview

PoE technology is governed by IEEE standards that define how power is delivered over Ethernet cables. The most relevant standards for PoE cameras are:

• IEEE 802.3af (PoE): Delivers up to 15.4W (12.95W usable) at 44–57V. Commonly used for basic IP cameras, access points, and VoIP phones.
• IEEE 802.3at (PoE+): Provides up to 30W (25.5W usable), ideal for PTZ cameras, video analytics devices, and dual-sensor cameras.
• IEEE 802.3bt (PoE++): Includes Type 3 (up to 60W) and Type 4 (up to 100W), used for high-power devices like pan-tilt-zoom (PTZ) cameras with heaters or IR illuminators.

Each standard influences how the four active wires are used, particularly in terms of voltage, current, and data/power coexistence.

Alternative A vs. Alternative B: Power Delivery Methods

The IEEE standards define two main methods for delivering power over Ethernet:

• Alternative A (Endspan): Power is delivered over the same wire pairs used for data (Pins 1–2 and 3–6). This is common in Gigabit Ethernet (1000BASE-T), where all four pairs carry data. Power is superimposed using phantom power techniques, allowing data and power to coexist on the same wires.
• Alternative B (Midspan): Power is sent over the spare wire pairs (Pins 4–5 and 7–8). This is typically used in 10/100 Mbps networks, where only two pairs are used for data. The spare pairs are dedicated solely to power.

Example: A 100 Mbps PoE camera connected to a PoE switch using Alternative B will receive power via the blue and brown pairs (Pins 4–5 and 7–8), while data flows through the orange and green pairs (Pins 1–2 and 3–6). This separation reduces interference and simplifies troubleshooting.

Which Method Is Used by PoE Cameras?

Most PoE cameras today are designed to work with both Alternative A and B, making them compatible with a wide range of switches and injectors. However, the choice often depends on the network infrastructure:

• Older or budget switches may only support 10/100 Mbps and use Alternative B.
• Modern Gigabit switches typically use Alternative A to maintain high-speed data rates while delivering power.

Tip: Always check your PoE switch or injector’s specifications to confirm which method it supports. Mismatched configurations can lead to power delivery failure or data corruption.

Data and Power: How the 4 Wires Work Together

Data Transmission Over Pins 1, 2, 3, and 6

In both 10/100 Mbps and Gigabit Ethernet, the primary data channels are Pins 1 (White-Orange), 2 (Orange), 3 (White-Green), and 6 (Green). These wires form two differential pairs:

• Transmit (Tx): Pins 1 and 2
• Receive (Rx): Pins 3 and 6

Differential signaling—where data is sent as voltage differences between the two wires in a pair—ensures high noise immunity and stable transmission over long distances. For PoE cameras, this means clear, uninterrupted video streams even in electrically noisy environments like industrial sites or parking garages.

Power Delivery: Phantom Power and DC Balancing

When power is delivered over the same wires used for data (Alternative A), the PoE system uses a technique called phantom power. Here’s how it works:

• Each data pair (Tx and Rx) carries both AC (data) and DC (power) signals.
• The transformer at each end (in the switch and camera) separates the DC voltage from the AC data signal.

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• Center-tapped transformers allow DC voltage to be applied equally to both wires in a pair, while the data signal remains differential.

This method ensures that the DC power doesn’t interfere with data integrity. For example, a 48V DC supply can be safely sent over Pins 1–2 and 3–6 without affecting the Ethernet signal.

Real-World Scenario: Troubleshooting a No-Power Issue

Suppose a newly installed PoE camera isn’t powering on. A technician checks the cable and finds continuity on all eight wires. However, a PoE tester shows no voltage on Pins 4–5 or 7–8. This suggests:

• The switch is using Alternative A (power over data pairs)
• The camera expects Alternative B (power over spare pairs)

Solution: Replace the switch with one that supports Alternative B, or use a PoE injector that matches the camera’s power requirements. Alternatively, ensure the camera firmware supports both modes.

Voltage and Current Considerations

PoE cameras typically require 44–57V DC and draw current based on their power class (e.g., 0.3A for 15W). Voltage drop over long cable runs (beyond 100 meters) can reduce effective power delivery. Using thicker cables (e.g., Cat6 with 23 AWG wires) or PoE extenders can mitigate this issue.

Why Only 4 Wires Are Typically Used (And When All 8 Matter)

The Efficiency of 4-Wire PoE

Using only four wires for PoE is a design choice rooted in efficiency and compatibility. Here’s why:

• Cost Savings: Fewer active components in switches and cameras reduce manufacturing costs.
• Backward Compatibility: 4-wire PoE works with existing 10/100 Mbps networks, which are still widely used.
• Thermal Management: Delivering power over fewer wires reduces heat buildup in cables, especially important in bundled installations.

For most standard PoE cameras (e.g., 720p or 1080p fixed cameras), 15–30W is sufficient, making 4-wire delivery ideal.

When All 8 Wires Are Needed: Gigabit PoE and High-Power Devices

As camera technology advances, the demand for power and bandwidth increases. This is where all eight wires become essential:

• Gigabit Data Rates: 1000BASE-T requires all four pairs for data, forcing power to be delivered over the same wires (Alternative A).
• High-Power PoE++ (60–100W): Devices like PTZ cameras with heaters, wipers, or dual IR/color sensors need more power. Using all eight wires allows higher current delivery while maintaining data integrity.

Example: A PoE++ PTZ camera in a cold climate may require 75W to power its motor, heater, and 4K sensor. The switch uses Alternative A, delivering 50V across all four pairs via phantom power. The camera’s internal circuitry separates power and data, ensuring smooth operation.

Future-Proofing Your PoE Network

When planning a surveillance system, consider future upgrades. A Gigabit PoE+ switch that uses all eight wires ensures compatibility with next-gen cameras, even if your current devices only use four. This avoids costly re-cabling later.

Common Mistakes and Best Practices for PoE Camera Wiring

Top Wiring Mistakes to Avoid

• Using Non-PoE Cables: While Cat5e/Cat6 cables are standard, cheap or damaged cables with thin conductors can overheat under PoE loads. Always use high-quality, shielded cables for long runs.
• Incorrect Termination: Miswired RJ45 connectors (e.g., swapping Pin 1 and 2) cause data loss or power failure. Use a cable tester to verify pinout accuracy.
• Exceeding Cable Length: PoE voltage drops significantly beyond 100 meters. Use PoE extenders or local power injectors for longer runs.
• Mismatched PoE Standards: A PoE+ camera on a PoE (802.3af) switch may underperform or not power on. Match camera power class to switch capability.

Best Practices for Reliable PoE Installation

• Use Certified PoE Switches/Injectors: Look for IEEE 802.3af/at/bt certification to ensure safety and compatibility.
• Label Cables Clearly: Mark each cable with camera ID and PoE type (e.g., “Cam-03, PoE+”) for easy troubleshooting.
• Test Before Deployment: Use a PoE tester to verify voltage, polarity, and data integrity at the camera end.
• Plan for Redundancy: In critical systems, use dual-power PoE switches or battery backups to prevent outages.
• Consider Environmental Factors: Outdoor cameras require weatherproof enclosures and UV-resistant cables.

Data Table: PoE Standards and Wire Usage

PoE Standard	Max Power	Voltage Range	Data Speed	Power Method	Wires Used
IEEE 802.3af (PoE)	15.4W (12.95W)	44–57V	10/100 Mbps	Alternative A or B	4 (data) or 8 (if Gigabit)
IEEE 802.3at (PoE+)	30W (25.5W)	50–57V	10/100/1000 Mbps	Alternative A or B	4 or 8 (Gigabit: all 8)
IEEE 802.3bt Type 3 (PoE++)	60W (51W)	52–57V	1000 Mbps	Alternative A (all pairs)	8
IEEE 802.3bt Type 4 (PoE++)	100W (71W)	52–57V	1000 Mbps	Alternative A (all pairs)	8

This table highlights how wire usage scales with power and data demands, emphasizing the importance of choosing the right PoE standard for your application.

Conclusion: Mastering the 4 Wires for a Smarter Surveillance System

Understanding the roles of the four wires in a PoE camera is more than a technical curiosity—it’s a cornerstone of effective security system design. Whether you’re leveraging the spare pairs (Pins 4–5 and 7–8) for power in a 100 Mbps setup or using phantom power over all eight wires in a Gigabit PoE+ network, the principles remain the same: data and power must coexist efficiently and safely. By grasping the nuances of PoE standards, wire functions, and installation best practices, you can avoid common pitfalls, extend equipment lifespan, and ensure crystal-clear surveillance footage.

As technology evolves, the line between “4 wires” and “8 wires” will continue to blur, especially with the rise of AI-powered cameras, multi-sensor systems, and edge computing. But the foundation—knowing how each wire contributes to power and data delivery—will always be critical. Whether you’re a homeowner installing a single PoE camera or an IT professional managing a campus-wide surveillance network, this knowledge empowers you to build smarter, more reliable, and future-ready security solutions. So the next time you plug in a PoE camera, remember: those four (or eight) wires are the lifeline of your entire system.

Frequently Asked Questions

What are the 4 wires for in a POE camera?

The 4 wires in a POE (Power over Ethernet) camera typically consist of two pairs: one for transmitting data and one for delivering power. This setup allows both power and network connectivity to be delivered through a single Ethernet cable, simplifying installation.

How does a POE camera use the 4 wires for power and data?

Two of the four wires carry power (usually 48V DC) from the POE switch or injector, while the other two transmit data between the camera and the network. This dual-purpose wiring follows IEEE 802.3af/at/bt standards for efficient, simultaneous power and data transfer.

Can I split the 4 wires in a POE camera to extend the cable?

Splitting the 4 wires isn’t recommended, as it disrupts both power and data signals. For longer runs, use a POE extender or switch to maintain signal integrity without modifying the original cable.

Why do some POE cameras have unused wires in the 4-wire setup?

Some manufacturers use 4 wires (2 pairs) for compatibility with older or non-standard POE systems, leaving extra wires inactive. Always check your camera’s manual to confirm which wires are used for power and data in your specific model.

Is it safe to connect only 2 of the 4 wires to a POE camera?

No, connecting only 2 wires may result in insufficient power or data transmission. All 4 wires must be properly terminated to ensure reliable operation of your POE camera system.

Do all POE cameras require the same 4-wire configuration?

While most POE cameras use the same 4-wire standard (two for power, two for data), pinouts may vary between active/passive POE. Verify your camera’s specifications to match the correct wiring scheme for your network equipment.