What Is PoE and How Do You Use It for Cameras, Phones and Access Points?

Installing a camera in a hallway, an access point on the ceiling or a phone on a desk normally means each one needs a power outlet, unless you deliver power over the same network cable. That is exactly what PoE (Power over Ethernet) does: the switch or power-sourcing device sends power to the device through the network cable, together with the data.

Benefits of PoE

• Simpler installation: No separate power wiring is needed for each device.
• Centralized backup power: Connect the PoE switch to a UPS and your phones, cameras and access points keep working during a power outage.
• Remote reboot: On a managed switch you can turn a port’s power off and on again, restarting a frozen device without climbing a ladder.
• Fewer adapters: Scattered power adapters are a common source of failures and clutter.

PoE Standards

These are the main standards defined by the IEEE:

1. PoE, 802.3af: Up to about 15.4 watts at the switch port; enough for most IP phones and simple fixed cameras.
2. PoE+, 802.3at: Up to about 30 watts; for many newer access points and more advanced cameras.
3. PoE++, 802.3bt: About 60 or 90 watts depending on the type; for PTZ cameras with heaters, high-power access points and some other devices.

Some power is lost along the cable, so the power that reaches the device is slightly lower than the switch output. Always check the device datasheet for the standard and wattage it needs. For example, some access points power on with standard PoE but only enable all their features with PoE+.

Watch out for non-standard PoE (Passive PoE). This equipment sends a fixed voltage without checking compatibility, and connecting it to an incompatible device can damage that device. Standards-based equipment checks the device on the other end before sending power.

Calculate the Switch Power Budget

Every PoE switch has a total power budget, which is often lower than the combined maximum of all its ports. A 24-port switch may offer PoE on every port, yet its total budget may not allow all ports to draw maximum power at the same time. To calculate:

1. List your devices and the maximum power draw of each from its datasheet.
2. Add up the figures and leave a safety margin and room for growth.
3. Choose a switch whose total budget is higher than that number.

On managed switches you can also set PoE priority per port, so that if power runs short, the most important devices stay on.

Practical Tips

• Cable length: As with any copper Ethernet link, a maximum of 100 meters.
• Cable quality: Use pure copper Cat6 cable or better; CCA cables run hotter and suffer more voltage drop when carrying PoE current.
• PoE injector: If you have no PoE switch, or only one or two devices, an injector adds power to a single cable; its standard must match the device.
• Ventilation: A heavily loaded PoE switch produces more heat, so the rack needs proper ventilation.
• UPS: Size the UPS based on the actual consumption of the PoE switches together with their connected devices, not the switch alone.

Checklist

• The standard and power required by each device are known.
• Total consumption is below the switch power budget, with a margin.
• Passive PoE equipment is not mixed with standards-based equipment.
• Pure copper cable, under 100 meters
• The PoE switch is connected to a UPS.
• PoE priority is set for critical devices.

ITPlus724 engineers can calculate the power your equipment needs and design and deploy the right PoE switches and infrastructure for your company.