Understanding PoE Switch Power Supply Limits: Why Is the Maximum Distance 100 Meters?

1. Introduction

Power over Ethernet (PoE) technology allows network switches to deliver both data and electrical power over a single Ethernet cable, simplifying deployments for devices like IP cameras, wireless access points, and VoIP phones. Major manufacturers like Huawei have advanced PoE switches (e.g., Huawei S5700 & S6700 series) that comply with IEEE standards while offering enhanced power management. However, PoE power transmission is typically limited to 100 meters (328 feet), the same as standard Ethernet data transmission. This article explains the reasons behind this limitation.

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Huawei S5735-L24P4S-A https://www.telecomate.com/s5735-l24p4s-a/

Huawei S6730-H24X4Y4C https://www.telecomate.com/s6730-h24x4y4c/

Huawei S6730-H28Y4C https://www.telecomate.com/s6730-h28y4c/

2. Why is PoE Power Supply Distance Limited to 100 Meters?

(1) Ethernet Cable Resistance & Voltage Drop

Ethernet cables (Cat5e/Cat6) have inherent resistance, causing voltage drop over long distances.

PoE standards (IEEE 802.3af/at/bt) specify 44-57V input, but devices typically require 37-57V to operate.

Huawei PoE switches use real-time voltage monitoring to optimize power delivery, but physical resistance limits remain.

Beyond 100m, voltage drop may cause insufficient power, leading to unstable performance or failure.

Example: A 48V PoE supply may drop to ~30V at 150m, below the minimum required voltage.

(2) Data Signal Degradation 

Ethernet signals weaken over distance due to attenuation and crosstalk.

The 100m limit ensures reliable data transmission (1Gbps/10Gbps) without excessive packet loss.

Huawei switches mitigate signal loss with advanced DSP chips, but 100m is still the baseline for stable operation.

Extending beyond 100m requires signal repeaters or fiber optic conversion, which may not support PoE.

(3) PoE Standards & Safety Compliance PoE

IEEE 802.3 standards define 100m as the maximum safe distance for PoE to prevent:

Overheating due to excessive current resistance.

Fire risks from high-power transmission over long cables.

Huawei’s iPower technology intelligently adjusts power output to meet safety certifications (UL/CE).

Exceeding 100m may violate safety regulations.

How to Extend PoE Beyond 100 Meters?

3. Huawei PoE Switches: Technical Advantages & Innovative Solutions

As a global leader in networking equipment, Huawei has optimized its PoE switches beyond standard specifications to enhance power delivery distance and energy efficiency. Below are the key advantages of Huawei PoE switches:

(1) Huawei iPower Intelligent Power Management
Dynamic Voltage Scaling (DVS): Automatically adjusts output voltage based on cable length and load, minimizing power loss over long distances.
Real-time Cable Diagnostics: Detects cable quality (e.g., resistance, capacitance) to prevent power instability caused by poor-quality cables.
Energy-saving Mode: Reduces power consumption during low-load conditions, complying with green energy standards.

(2) Huawei Long-Reach PoE Technology
Supports >100m Power Delivery (Up to 150m): Achieves extended range via enhanced signal modulation on Cat6A or higher-grade cables.
Backward Compatibility: Works with standard PDs (e.g., IP cameras, APs) without hardware replacement.
Use Cases: Campus surveillance, industrial automation, smart agriculture.

(3) Huawei PoE++ (IEEE 802.3bt) High-Power Solutions

Up to 60W per Port: Powers high-demand devices (e.g., PTZ cameras, wireless base stations).
4-Pair Power Delivery: Utilizes all wire pairs to reduce heat generation.
Thermal Protection: Prevents switch damage from overload or overheating.

4. Deployment Best Practices: Maximizing PoE Range

5. Conclusion

The 100-meter limit for PoE is due to voltage drop, signal integrity, and safety regulations. Huawei’s innovations push boundaries in specific scenarios, but standard deployments should adhere to IEEE guidelines. For optimal performance, follow IEEE standards and use high-quality cables (Cat6A for lower resistance).