PoE power supply distance and network cable selection points
Explain the PoE standard, the origin of the 100-meter limit, the over-distance solution, and the actual impact of network cable materials on power supply and stability.
PoE Standard
| Standard | Power supply (PSE output) | Common applications |
|---|---|---|
| IEEE 802.3af (PoE) | 15.4W | Ordinary gun / hemisphere |
| IEEE 802.3at (PoE+) | 30W | Dome machine, heating equipment |
| IEEE 802.3bt (PoE++) | 60W / 90W | High-power dome machine, multi-sensor equipment |
Note: The nominal total PoE power of the switch must be greater than the sum of the power of all powered devices, leaving a 20% margin. When the dome machine starts heating at low temperature, the power will increase significantly and must be calculated based on the peak value.
The origin of the 100-meter limit
The Ethernet standard specifies 100 meters as a reliable distance for data transmission (90 meters horizontally + 10 meters patch cord). The PoE power supply distance is affected by the voltage drop of the wire diameter, and the actual usable distance is often shorter, especially in high-power equipment.
Network cable selection
- Oxygen-free copper must be used: Copper-clad aluminum and copper-clad iron wires have high resistance, and long-distance power supply will cause the equipment to restart repeatedly.
- Category 5e (Cat5e): Short distance (≤60 meters), available for ordinary cameras, high cost performance.
- Category 6 (Cat6): Recommended, with thicker wire diameter, better power supply and anti-interference, suitable for dome machines and long distances.
- Outdoor cable: Choose special outdoor cables that are water-resistant and UV-resistant, or protected by pipes.
Common wire diameter and voltage drop reference
| Wire gauge | Conductor diameter | 100-meter resistance (single core) | Evaluation |
|---|---|---|---|
| 24AWG | About 0.51mm | About 8.9Ω | Standard Category 6, available |
| 23AWG | About 0.57mm | About 6.9Ω | Recommended, small voltage drop |
| 22AWG | About 0.64mm | About 5.3Ω | Long distance/high power preferred |
What to do if the distance exceeds 100 meters
- Add switch trunk: Add an industrial switch every 100 meters, which is stable and reliable (recommended).
- Optical fiber + transceiver: The first choice when the distance is long and the anti-interference requirements are high, and the remote power supply needs to be solved separately.
- PoE extender: It can be extended by another 100 meters, suitable for retrofitting.
- Increase the wire diameter: Change to 22AWG Category 6 wire and it can be extended to 120~150 meters, but you need to pay attention to signal attenuation.
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