PoE (Power over Ethernet) is a function that enables the Ethernet cable to transfer both power and data (via the same cable). Basically, using PoE you can power devices without the need of using a separate power supply, one cable is able to power up the device and transmit the data as well.
PoE technology allows the installer to use less cabling when installing the system and overall it will reduce the maintenance costs while increasing the reliability of the setup.
Spots previously inaccessible for camera installation due to their remote situation from power outlets now become available. Moreover, PoE cable runs on the ceiling or on a wall will not be bulky or ugly. However, then using this feature, you need to understand the difference between Active PoE and Passive PoE.
The difference between Active PoE and Passive PoE
An important aspect of the PoE function is how the power is delivered via the network cables. These specs have been regulated to ensure a safe transfer of the power from the PoE switch/injector to the camera/receiver.
Apart from sending out a safe voltage range, the devices need to communicate to approved procedures. Before delivering the power, the PoE power supply unit will test out the connection using the 802.3at procedure.
If everything is correct, the devices will do a “handshake”, which indicates that the power is compatible between the PoE sender and the receiver side. If there’s no handshake, no power will be delivered.
That’s basically what consists of an Active PoE and a Passive PoE. In other words, passive PoE describes power supplies (such as PoE switches or PoE injectors) that send raw unnegotiated power via the ethernet cable to the connected devices.
The receiver unit will receive the power without checking if it’s compatible with its requirements. So, there will be no handshake or no verifying procedure. A passive PoE is known as an “always ON” device, meaning it will receive the power that is being delivered to it.
On the other hand, Active PoE means that a device is rated to be 802.3af or 802.3at compliant. These specifications require the PoE power supply unit to perform a spec verification or “handshake”.
As we said, passive PoE does not perform a handshake, so it’s very important to know what PoE voltage your device (such as a camera) requires before powering it up via a PoE power supply.
Otherwise, if you connect the wrong voltage you may cause permanent damage to the device (possibly burning the motherboard).
There are three IEEE 802.3 standards for active PoE that are used in regular and PTZ security cameras:
- PoE (802.3af): Provides 15.4 W of power
- PoE+(802.3at): Provides 30 W of power
- PoE++(802.3bt): Provides 60 W and 90 W of power
Difference between active PoE and passive PoE in security camera systems?
- When using an active PoE, the camera/gadget will not power up until it completes a handshake between the PoE power supply and the device.
- The camera will not get powered up if the handshake is not approved.
- When using a passive PoE, the camera will get powered up regardless of its power parameters. Since there’s no handshake the camera may get burned if it’s receiving a higher level of voltage.
How to reduce the risk of Passive PoE?
To reduce the risk of passive PoE power supply units, you need to ensure that the power supply provides the correct voltage for the IP camera (or any other smart device). Check the camera specs, note what wattage it requires and then ensure the PoE switch/injector will provide the required power.
For example, regular IP cameras are able to handle wattages up to 15W. If the PoE switch provides 15W and less, then the camera will get powered normally and there’s no risk of getting damaged.
The IP cameras usually require 9W wattage, the more IR light on the camera, the more wattage required. Generally, they require 9-15W.
Obviously, if the PoE switch will send 90W to a camera that can handle 15W only then the camera will get damaged. That’s why it is important to check the power levels when using passive PoE power supply units. If you’re not sure, you may ask the seller or the manufacturer for assistance.
When using active PoE, there’s no need to worry about checking any parameters because the units (sender and receiver) will automatically check the parameters. If no there is no handshake established, then no power will get injected.
Recommendations and Conclusion
PoE feature is a very convenient function that helps lower the installation cost and maintenance of your security system. It can be used in various situations around your house or business.
When using a PoE power supply, we always recommend using an Active PoE to power up your devices. This way, the PoE power supply, and the smart devices will automatically check (“handshake) if the voltage and other parameters are compatible. If so, the power will be delivered and the device will work correctly.
A PoE power supply that supports IEEE 802.3af can provide 15.4W of power. If you have any device that requires more than that (such as a PTZ camera), then it should not be connected to a regular PoE supply, but to a PoE+ unit that provides higher wattages.
Another thing to consider is the cumulative power consumption of the devices connected to a PoE switch. Let’s say you have a PoE switch that outputs 90W of power, then the total power of the cameras (and other devices) connected to this switch should be less than 90W.
If the camera draws more power, the switch can provide enough juice, and subsequently, the devices may not work correctly.
To conclude, you need to understand the difference between active and passive PoE. If you’re using a passive PoE power supply, ensure the wattage is supported by the receiver’s side.
However, we’d recommend using an active PoE power supply that verifies the parameters with the device before delivering power to it.
