Everything you need to know about Power over Ethernet (PoE)

Power over Ethernet is a technology that allows you to send both power and data over twisted-pair Ethernet cables. The edge devices such as IP Cameras, VoIP Phones, and Wireless Access Points can be powered by the same cable that connects them to a network.

The IEEE PoE earliest standard is 802.3af-2003, which provides 15.4 watts of DC power over standard Cat3 and Cat5 network cables. However the newer devices required more power, so a new standard was created in 2009 – IEEE 802.3at – with a maximum of 30W and 25.5W remaining power budget actually reaching the devices. These standards still exist today and are often sold to help you easily get started with your PoE installation. The latest standard IEEE802.3bt employs all 4 twisted pairs to send the power which makes the maximum power output come to 90W and the remaining power budget still have 71W at the edge.

What is PoE++?

The latest update to Power over Ethernet is the IEEE 802.3bt standard, known as PoE++. The major difference between PoE++ and PoE+ is that PoE++ power sources can provide over twice as much power to their PDs.

The PoE++ takes all 4 twisted pairs to send the power, and PoE/PoE+ only uses half (2 twisted pairs) to transfer the power.

In order to achieve 71W high power, both PSE (PoE switch or injector) and the PDs (IP camera, access point) must compatible with the latest standard. If the PoE switch only supports PoE+, the switch will not supply enough power and the whole link will downgrade to PoE+. The latest standard is backward compatible with PoE+/PoE.

How Does Power Over Ethernet Work?

In the fast network (10/100Mbps), only half of the twist pairs are being taken to transfer the data. It leaves two spare twisted pairs which can be used to send the power. This is a very primitive idea to design the PoE system. Actually, the passive PoE system still uses this method to send the power over an Ethernet cable.

With IEEE802.3 specification, one important mechanism – power handshaking was added to the system. The PSE (PoE switch and injector) need to verify and classify the edge device before it releases the power over the Ethernet cable. If the PSE can’t verify the edge device is PoE compatible, it will not send the power.

Now the PoE camera can go through the same twisted pair as the data. It is the PDs’ job to split the power from the data. According to IEEE802.3, the PDs should be able to accept power from data pairs (12-36) or spare pairs (45-78). Some of the products like the access point don’t fully implement the standard and keep the spare pairs (45-78) for passive PoE (24VDC). It will create an unexpected issue when the PoE++ switch is being used to supply power because the PoE++ switch will send 48V through all 4 twisted pairs.

How to Upgrade to Power Over Ethernet?

Adding PoE to your network is as straightforward as it gets, and there are two ways you can do so——POE switches and a POE injector:

PoE switches are network switches that have a Power source built-in. Simply connect PoE compatible IP devices to the switch, and the switch will automatically detect whether they’re compatible with PoE or not and enable power, there is power handshaking we mentioned above.

PoE injectors are devices that can convert non-PoE-switch to PoE compatible. These devices aren’t as powerful as PoE switches, but they work in a pinch. The PoE injector takes its power from an AC power source and converts it into the correct voltage for a PoE device. A POE injector is typically either a multi-port rack-mounted unit or a single port injector that is connected via a patch cable.

It’s also possible to upgrade non-PoE PDs such as IP cameras with PoE using a PoE splitter. The PoE splitter takes the network connection from the cable and taps it off before converting the power into the DC low voltage used by the camera.

How Much Power can PoE Devices supply?

PoE+ devices supply a maximum of 30 watts per port, while PoE devices supply a maximum of 15.4 watts per port, PoE++ the latest standard supplies 90 watts, but that’s not all. Some power will get lost over the length of the cable; the longer the cable, the more power will lose.

The lowest guaranteed power available at a PD is 12.95 watts per port for PoE, 25.5 watts per port for PoE+ and 71W for PoE++.

PSEs also have a maximum budget, which can be measured in watts. Most PSEs don’t have enough power budget to give every PoE-capable PD all the power they want, because most people don’t need all that much. Usually, the PoE switch shares the power source. Just make sure you calculate your needs before you buy a PoE-capable PSE.

What Are the Benefits of Using PoE?

Power over Ethernet (PoE) is a way to send both power and data over a single Ethernet cable. It is typically used to provide both electricity and data to network devices such as PoE Wireless Access Point, PoE Switch, PoE IP Camera, VoIP phones, and networking equipment. Moreover, PoE has many economic and efficiency benefits for businesses of any size.

Cost efficiency-You don’t have to hire a specialized electrician or spend money on network installation costs to install PoE.

Time savings-Power over Ethernet doesn’t require electrical power cabling to be installed and it doesn’t need a qualified electrician to fit network cables, saving both time and installation costs.

Quick deployment-Power over Ethernet eliminates the need to have an expensive electrical contractor come in, and is easy to set up and reposition.

Flexibility-As power isn’t always needed from an electrical outlet, you can place your devices where they are most needed even the AC outlet doesn’t present nearby.

Safety-Electrical power can be delivered via 48VDC which is considered safe by UL standards. PoE also has built-in safety features, such as if there’s a disruption in power, the PSE automatically stops sending the power.

Reliability-As a company or user, if you’re using PoE, you don’t have to worry about what device is plugged in where, as every device gets power from the network. This also means that the installation and distribution of network connections are super easy and effective. It’s easy to control the power supply to disable or reset devices, too.

Scalability-When installation and distribution of network connections is simple and effective, this makes connecting new offices simpler as well. This means that there is a cost-effective way for businesses to grow in the future.

Security-As PoE devices attached to networks with high-level security enjoy the same security protection as other network assets, Power over Ethernet devices do not rely on security from the device itself but rather from the network.

Devices that use Power over Ethernet

As technology advances, and we’re being pushed further into the Internet of Things (IoT) and connected devices, the range of products and equipment that can be powered by PoE has been increasing. Power over Ethernet supports the following devices:

VoIP Phones-The original PoE application. For an IP phone to work, it must be connected to a power outlet and have a single connection to a wall socket. It can also be remotely powered down if it doesn’t need to be used, just like with older analog systems.

IP Cameras-The use of IP cameras has spread throughout the world and has become an industry standard for fast and easy installation. This has ensured that small to large-scale security systems can be created.

IP Intercoms– IP intercoms can use PoE, as they’re door intercom systems that work in the same way as a “IP camera”, transmitting power and data signals over the same network cable.

IP Speakers-These are the latest audio systems for music and public addresses, where the entire audio system is connected via a LAN or WAN network. This allows the IP speakers to be connected via Ethernet cable, along with Ethernet power from a PoE switch.

Wireless IP Access Points-Wi-Fi, Bluetooth, and RFID readers are all devices that are commonly PoE compatible. This allows them to be remotely located or relocated, wherever there is access to power over Ethernet.

What Are PoE Standards?

IEEE 802.3at, IEEE 802.3bt, IEEE 802.3bt+ and IEEE 802.3af are power supply standards released by the IEEE to ensure interoperability across a broad range of devices (PDs) and power sources (PSEs). They help devices and power sources operate at the same voltage levels but deliver different wattage. What’s the difference between the four standards?

  1. Power over Ethernet (PoE)-The IEEE 802.3af standard supplies up to 15 watts of DC power from a Power Source Equipment (PSE) to PoE-enabled devices and 12.95 watts from the PD to a powered device because of losses on an Ethernet cable. It uses two pairs of wires like CAT3 or CAT5 cables as a medium.
  • Power over Ethernet Plus (PoE+)-The IEEE 802.3at standard is also referred to as High PoE supplies power up to 30 watts of DC power from PSE and 25.5 watts from PD because of losses on an Ethernet cable. It also uses two pairs of wires such as CAT5 cable or higher as a medium.
  • PoE++- The latest IEEE standard after IEEE 802.3af & 802.3at standards for taking all 4 twisted pairs to send the power. PoE++ supply up to 90 watts of DC power from the PSE and 71 watts from PD due to losses in the cable. This standard uses four pairs of wires as a medium, like traditional CAT5e or CAT6 cables.

Is Power over Ethernet Safe to Use?

IEEE 802.3af/at/bt-compliant PoE (Power over Ethernet) technology is safe and is not a threat to any device that’s not designed to work with PoE. If a PSE intends to send power, it initiates a handshake procedure with the PD (Power Device), which establishes how much power the PD requires.

This handshake is harmless, and can only be completed if there’s a PSE and PD on both ends of the cable. If this handshake isn’t completed, then no power is sent to either device – making it inherently safe. However, the passive PoE system which removes the power handshaking could cause harm to your edge device. There is a significant difference between the standard PoE and passive PoE.

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