Power over Ethernet Switch: Passive PoE Vs Active PoE

Power over Ethernet (PoE) is a technology for wired LANs. This allows a single cable usually Ethernet cable to provide both data connection and electric power to devices such as IP cameras, NVR recorders, wireless access points, etc. A PoE switch, compared with other Gigabit network switches, has power over Ethernet injection built in. This feature allows end-user to power PoE capable devices without the need for a separate power supply or the need for an electrical outlet near the powered device. If you have read about the http://opticalfiberalsa.over-blog.com/2017/09/how-to-understand-poe-and-poe-switches.html, you must know clearer about the difference between PoE and PoE+ switches. However, today’s article will help you understand active PoE and passive PoE.

What is PoE Switch?

As mentioned before, a PoE switch not only supply power to devices but also carries network connection. In general, a PoE switch usually contains multiple Ethernet ports, e.g. a PoE switch with 8 ports, PoE switch with 16 ports, 24 ports PoE switch, or PoE switch with 48 ports. If you are looking for PoE switch to cover all your devices, it’s important to check the port number first.

The following image shows the 8-port PoE managed switch.

Passive Power over Ethernet vs. Active PoE

To safeguard a voltage range, the Power over Ethernet devices must communicate according to established procedures. In simple terms, active PoE refers to any type of PoE that negotiates the correct voltage between the switch and PoE-powered device. Passive PoE does no such negotiation, and as such is always sending electric current out over the Ethernet cable at a certain voltage regardless of the device it’s going to.

Active PoE

If your PoE switch uses 48V 802.3af or 802.3at standard, it is considered to be active PoE. The power supply unit inside the active PoE switch usually tests the connection before providing the supplying voltage, meaning that PoE switch will check the power coming in, and if it doesn’t meet the device requirement, it won’t power up.

Passive PoE

Passive PoE refers to any devices using PoE that is not 802.3af or 802.3at. Unlike active PoE switch, In passive PoE, no negotiation takes place between the two devices, but instead the known cable layout is used from Standard 802.3af, mode B. Therefore, it is extremely important to know what PoE voltage your devices requires before plugging in the Ethernet cable and powering it up. If you connect the wrong voltage, you may cause permanent electrical damage. Passive PoE is like plugging a 120V appliance into a 240V outlet, but with devices than cost much more than a simple toaster.

Conclusion

The big advantage of Power over Ethernet switch is that it allows greater flexibility in locating devices, as you don't have to be situated near a power source—power is carried to them right in the Ethernet cable. That also frequently results in significantly lower installation costs, especially where many Access Points must be setup. The difference between Passive PoE and active PoE switch is quite obvious. For more, you can go through previous articles.

Power Supply: POE Switch for IP Camera

PoE switch, as the previous article describes, provides power and data to all PoE devices, including IP cameras, NVR recorders, computers, and VoIP phones, etc, via a single Ethernet cable (Cat5, Cat5e or Cat6). A PoE switch normally comes with multiply ports to support more than one IP camera. There are two types of PoE standards, one is IEEE802.3at, the other is IEEE802.3af. The major difference between them is that PoE+ standard (IEEE802.3at) can pump out up to 30 W per port, whereas PoE standard (IEEE802.3af) can provide up to 15.4 W per port. The question is how to choose or select a best PoE switch for your IP cameras in the perspectives of power supply.

Understand IP Camera Power Needs

The power consumption of PoE IP cameras varies owing to different types e.g. pan-tilt zoom (PTZ) cameras, Dome IP cameras, CCTV cameras, IP cameras with IR illumination night vision, etc. PTZ camera could draw up to 20 Watts, while other IP camera could consumes as little as 3 or 4 Watts. Therefore, a PoE switch should be able to provide enough power for different types of IP camera via Cat 5 or Cat 6 cables.

Although Security cameras, either CCTV cameras or PoE IP security cameras, are not energy-consuming as other gadgets like computers or TVs; they only need a very little electricity to work, you still need to count it in. Remember to double check your PoE IP camera power consumption ether in the user manual or technical specification spreadsheet.

To provide the proper amount of power for PoE IP cameras, another important feature to look for in a PoE switch for IP cameras is its abilities to automatically adjust voltage accordingly. Many security cameras run either 12V or 24V power, if not supplied with the proper power voltage, the IP camera either won’t work or even be overloaded.

Maximal Power Supply of PoE Switch

Besides the power consumption of IP cameras, the maximal power supplies of your PoE switch matters as well.

If the maximal power supply of all your cameras exceeds your PoE switch power cap, then the PoE switch won’t provide enough power for your PoE IP cameras, pan-tilt-zoom (PTZ) IP cameras in particular. Insufficient power supply to the IP cameras are the common culprits for video loss and IP camera poor performance.

That being said, when buying a PoE switch for IP cameras, it’s important to go for a PoE switch with more power juice or reducing the number of PTZ IP cameras plugged into the PoE switch as PTZ cameras draw more power than other IP cameras.

Can Cat5 Ethernet Cables Cover PoE Transmission Range?

The transmission range of PoE network is 100 meters. PoE IEEE802.3af standard requires powered sourcing equipment (PSE) output power is 15.4W, after 100 meters transmission, the powered devices (PD) can receive 12.95W power. According to 802.3af standard current value-350ma to calculate, the resistance value of 100 meters Ethernet cable should be (15.4-12.95W)/350ma = 7 Ohm or (15.5-12.95)/350ma = 7.29 Ohm.

Obviously, Cat5 Ethernet cable can meet the requirement, but nowadays customers tend to use Ethernet cable Cat5e.

Conclusion

PoE switch is not only the device that provides data connection and electric power to IP cameras, but other PoE devices such as wireless access points, VOIP phones, and NVR recorders. Therefore, when choosing PoE switches, you should count all the devices that you meed to connect with. As a professional telecom supplier, our products including IP cameras, PoE switches and Cat5 cables, are thoroughly tested for use with video surveillance equipment. If you have questions about which PoE power supply is recommended for your security application, please contact us directly.

Original Source: www.fiber-optic-solutions.com