IP devices require both power and network connections, which traditionally are run separately. However, it is becoming more and more common for devices to support Power-over-Ethernet (PoE), which offers a method for delivering both power and network connectivity over a single cable. Today, IP Phone Systems, Wireless Access Points, Security Cameras, Motion Detectors, Touch Panels, Thermostats, and Lighting Controls are all available with PoE support, making it an attractive option for home automation, AV and security installers. PoE offers installers a tremendous advantage in delivering flexible, reliable and cost effective solutions.
What is PoE?
PoE is the delivery of low voltage DC power over the same media used for data transmission on CAT5, CAT5e or CAT6 Ethernet cabling. There are three widely used PoE standards:
- Legacy PoE—provides a full 48 VDC and 48 Watts at all times
- 802.3af—provides 48 VDC with a maximum of 15.4 Watts
- 802.3at (also known as PoE+ or PoE plus)—provides 48 VDC with a maximum of 25.5 Watts and is backwards compatible with 802.3af devices.
It is important to note that 802.3af/at source devices (i.e. Switches, Midspans, and Power Injectors) are only compatible with 802.3af/at client devices and will not supply power to Legacy client devices. This is because 802.3af/at requires 2-way communication between the source and client device as part of the 802.3af/at standard. However, most 802.3af and 802.3at client devices are backwards compliant with Legacy PoE sources. In planning an installation and selecting which products to use, it’s also important to recognize that an 802.3af client can work with an 802.3at source, while an 802.3at client can only work with an 802.3af source if the client’s maximum power usage does not exceed 15.4 Watts.
PoE combines data and power inputs into a single output over standard Ethernet cable
Why Use PoE?
PoE is a rather flexible and cost-effective way to provide data and power to a remote location or to simply streamline an AV, control, and/or security installation. Some of the benefits include:
- Cost savings – Only one Ethernet cable is required for both power and data. There is no need for expensive AC lines or additional breakers.
- No electrician needed – PoE is considered low voltage DC power, which does not require a licensed electrician to install.
- Flexibile installation – Devices can be located up to 100 meters (328 feet) away from the PoE source, making it easy to place devices literally anywhere, including outdoors using outdoor certified Ethernet cable.
- Easy device reset – Devices installed in hard to reach areas can be easily rebooted
Where would I use POE?
PoE supported devices are becoming more common in nearly every facet of home and business networking. As the demand for better connectivity rises, having one solution that allows for centrally managed power and data can lower the overall installation and ongoing administration costs. A few areas where PoE can be especially useful include:
- In existing homes where running new wiring can be a challenge
- Remote outdoor locations (i.e. connecting an entry gate or remote IP camera)
- Wherever AC power is not readily available
- In cases where devices that are not easily accessible may need to occasionally be rebooted or powered off
How do I pick the right PoE source device for my installation?
The first thing you need to know is how many PoE devices will be used in the installation, as well as the peak wattage requirement for each device. You will also need to determine if the devices are 803.3af or require the higher wattage 802.3at PoE plus standard. This information should be specified on the client device.
Once you have identified and determined this information, you can now evaluate and determine the best PoE source option. In general, there are three types of PoE source devices:
- Switches: PoE Switches come in a variety of different options, so you need to be aware of what you are buying. For example, a switch may be advertised as a 24-port PoE switch, when in fact, only 8 of the ports are PoE, while the other 16 ports are Ethernet only. Others may only allow for some of the ports to be connected at full 802.3af or 802.3at output levels. Some switches are managed (allowing you to remotely turn power to PoE client devices on or off), while others are unmanaged. There are also performance differences between switches, with some supporting 10/100 Ethernet speeds and others running at full Gigabit speeds.
- Midspans: A PoE Midspan is a passive multi-port power injector that sits inline between a regular Ethernet switch and the powered device, injecting power without affecting the data. Midspans are used when there is no desire to replace and configure a new Ethernet switch, and only power needs to be added to the network.
- Injectors: A PoE Injector is basically a single output Midspan.
PoE source options include Switches, Midspans and Injectors
When selecting a PoE source device, be sure to always check the power load capabilities. Many PoE switches limit power up to a certain output limit. For example, if you have 60 Watts of power available across 8 ports and you have 4 devices that use 15 Watts each, you will end up with 4 useless PoE ports. So, when looking at PoE switch specifications, be sure that there is enough power to handle all ports running at full capacity. As an example, the Luxul XMS-1008P 802.3af switch has a 120 Watt power supply that allows all 8 ports to run at full 802.3af standards. Also, it is a good rule of thumb to plan for new devices being added to the system in the future. So, be sure to choose a source device that will leave you some available ports and power capacity.
Selecting the right PoE source device requires some homework in order to become familiar with the various options. However, it’s worth the effort. Because it offers simple, cost effective and flexible installation options in otherwise inflexible environments, PoE is becoming a “must have” solution for installers of automation, AV, and security systems.