What is the maximum transmission distance of PoE power supply?

Whether it's network cameras (IPCs) in security surveillance or wireless access points, access control devices, and VoIP phones in smart offices, they're increasingly relying on PoE technology to meet the dual needs of "data and power."

However, in actual deployments, a core question often arises:

👉 What is the maximum transmission distance of PoE power?

Is it 100 meters? 200 meters? Or indefinitely? Will the equipment still operate stably beyond this distance? Today, we'll explore the reasons.

What is PoE?
PoE, short for Power over Ethernet, refers to the simultaneous transmission of data and power over a network cable (typically a twisted pair). This eliminates the need for separate power cables; a single network cable allows for both internet access and power consumption.

Typical Application Scenarios:

• Wireless APs in offices
• Surveillance cameras in residential areas
• IP phones in enterprises
• IoT devices such as access control systems and smart terminals
The emergence of PoE has significantly reduced installation complexity and costs while increasing network flexibility.

How PoE Works
The power provider in PoE is called a PSE (Power Sourcing Equipment), typically a PoE switch or PoE injector. The powered device is called a PD (Powered Device), such as a camera or access point.

Power Supply Process:

1. Handshake Identification: The PSE first detects whether the PD supports PoE to prevent incorrect power supply.

2. Classification and Grading: Power is allocated based on the PD's power requirements (different standards have different power levels).

3. Continuous Power Supply: The voltage is stabilized between 44 and 57V and transmitted over the network cable.

4. Power Failure Protection: If the device is unplugged, power supply is immediately terminated.

PoE Standards and Power Capacity
Different PoE standards determine power capacity and also affect maximum distance.

Common standards are as follows:

As we can see, PoE technology has evolved from its initial 15W to nearly 100W, greatly expanding its application range.

PoE's theoretical maximum transmission distance 📏
📌 The IEEE standard clearly states that the maximum transmission distance for PoE is 100 meters.

This is because PoE relies on Ethernet twisted-pair cabling, and the Ethernet physical layer specification stipulates:

Maximum network cable transmission distance = 100 meters

• 90 meters of which are horizontal cabling (from the switch to the information panel),
• 10 meters are patch cables (between the two devices).

This 100-meter limit is not just a power issue; it is primarily determined by signal attenuation in Ethernet data communications.

Why can't the distance be extended indefinitely?

1. Resistive loss: The longer the cable, the greater the resistance, and the more significant the voltage drop. Beyond a certain distance, devices may experience insufficient voltage and restart.

2. Signal attenuation: Ethernet data transmission over distances exceeding 100 meters experiences a significant increase in bit error rates, leading to network instability. 3. Safety Standards: IEEE standards set the maximum transmission distance at 100 meters for compatibility and reliability.
Thus, the theoretical maximum PoE transmission distance is 100 meters.

What if the transmission distance exceeds 100 meters?

If a project requires PoE power over a distance of more than 100 meters, common solutions include:

1. PoE Repeater
• Working Principle: Receives the PoE signal, regenerates it, and transmits it further.
• Advantages: Simple and low-cost.
• Disadvantages: Each repeater causes a certain amount of power loss, and a maximum of 2-3 repeaters are required.
• Extended distance: 100m → 200m → 300m.

2. PoE Fiber Transceiver
• Uses fiber optic cable to transmit data over long distances, then provides PoE power output at the remote transceiver.
• Suitable for large-scale campus and surveillance projects.
• Transmission distances can reach several kilometers.

3. Tiered PoE Switch Deployment
• Add a PoE switch in the middle to both relay the network and regenerate power.
• Suitable for tiered layouts within building weak current rooms. 4. Independent Power Supply + Data Transmission via Ethernet Cable
• When the power consumption is extremely high or the distance is long, directly power the device independently and use the Ethernet cable only for data transmission.