The ABCs of PoE

Integrators have a real advantage with increased installation flexibility and lower labor cost

With the introduction of IP cameras, system integrators have experienced big improvements in the quality and performance of video systems that can be offered to their customers. Networking technology, however, requires integrators to learn new terminology and methods in designing and installing an efficient and reliable system.

One area of this technology that is proven to provide a real benefit is PoE.

What is PoE?

Power over Ethernet is an extension of the same concept used in the telephone industry, where voice and power are applied to the same cable. The 48VDC voltage used in plain old telephone service (POTS) analog circuits is what is commonly used for today’s PoE systems. In fact, the first standard adopted by the Institute of Electrical and Electronics Engineers (IEEE) came from a well-known telecommunications company’s research division.

Currently, there are two standards approved by the IEEE. The first, approved in 2003, is IEEE 802.3af and specifies up to 15.4 watts of direct current (DC) power. The second standard, ratified in 2009 as IEEE 802.3at, is commonly called high power PoE (HPoE) or PoE+ and doubles the power capabilities to 30 watts. Both standards have a maximum distance of 100 meters (328 feet) that is dictated by the distance limitation of Ethernet network cable. This standard is designed to be plug-and-play; however, there are some caveats to be aware of.

A basic PoE-based system consists of three main components:

  1. Power-sourcing equipment (PSE), such as a PoE network switch.
  2. Category network cable.
  3. A remote-powered device, which may be an IP camera, IP access panel,

IP intercom, VoIP or wireless access point (WAP).

Power-Sourcing Equipment

Power-sourcing equipment is a device that injects power onto the same network cable that is being used for data. The injector can be a stand-alone single-port or multiport device, or the injector can be built into a network switch. The second option is more common today due to the convenience of using a single integrated device.

The network switch is the heart of an IP video system. The data from IP cameras, NVRs and video management systems (VMS) streams all travel through the switch. Therefore, a high-performance switch with a non-blocking high-bandwidth switch fabric is certainly an important consideration in network design. Integrators using PoE technology need to understand that the PoE switch is not just handling data transmission, but also serving as the centralized power source for the video surveillance system. Selecting a PoE switch with sufficient power capability is critical in designing an efficient and reliable power grid for powered devices.

Although PoE is primarily designed as a plug-and-play technology, not all PoE switches are designed to deliver the full demands of maximum PoE on each port. PoE switches are sold at different price points, and it’s easy to make a purchase decision based on the lowest price. The cheaper PoE switch will typically have a less robust power supply and may not provide the full power required by PoE endpoints.

Category Cabling

PoE uses the same category network cable that is used for data. A category cable has four pairs (eight wires) inside, with two of the pairs used for data, leaving the open two pairs to be used for power.

When planning power needs, take into account power loss due to voltage drop on the cable. To help understand the specified power at the switch versus what is available at the endpoint, let’s look at the IEEE802.3 PoE standards (which are shown above in Table 1):

The security industry is accustomed to working with 12VDC/24VAC voltages, and sometimes integrators want to use their existing analog power supplies or don’t understand why 48-56VDC is required for PoE devices. Since the wire gauge in PoE category cables is smaller than those typically used for analog power, a higher voltage is needed for two reasons: to overcome a greater resistance and to limit the current flow.

If enough voltage isn’t injected at the source to overcome the increased resistance/ voltage drop, then there won’t be sufficient power at the PD end. At the same time, with too much current flowing in the cable, there’s a potential fire safety hazard due to the possibility of the cable overheating.

Remote-powered Device

When selecting a PoE switch, it’s important to understand the power requirements of the endpoint PDs and to select a switch that has sufficient power to meet the total demands of the system.

Just about any PoE switch will state on the box that it “supports up to 15.4W per port” (or 30W for PoE+). But, the key PoE switch specification to review is the switch’s “total power budget” specification.

Even a switch with a limited power budget can provide up to 15.4W per port, but the actual total number of ports that the switch can provide full power to may be limited based on the total power consumed by the powered devices. That means the switch may not have enough power to meet the demand of all ports.

For example, an eight-port switch may correctly claim to provide up to 15.4W of power per port, but have a total power budget of only 70W. The maximum number of ports for which the switch could provide a full 15.4W of power would be about four ports. Since many small form factor IP cameras operate at around 4 to 6 watts, a PoE switch with the above power budget configuration may work initially, but if higher-powered cameras using infrared LEDs or PTZ control, or require an enclosure, heater or blower are added, the power budget may become insufficient. Customers won’t understand why portions of their IP video system go down each night when the newly added infrared cameras are activated.

Advantages for Integrators

Security integrators gain significant benefits from PoE through increased installation flexibility, lower labor cost and improved reliability. For example, since the power is remotely distributed from the network PoE switch, the need to consider an IP camera’s proximity to an AC outlet is eliminated. This allows increased installation flexibility while lowering installation and labor costs by reducing or eliminating the need to subcontract an electrician to install AC electrical outlets. Some real-world examples of this are as follows:

  • The CTO of a U.S.-based healthcare system estimated that he saved $600,000 in setup costs by installing 200 access points powered by PoE instead of 110-volt AC outlets in his company’s hospitals; and
  • a university in Indiana installed 1,100 wireless access points powered by PoE, saving $350 to $1,000 per installed access point by eliminating labor costs incurred from contracting an electrician to run wiring for new AC outlets.

Also, using a managed PoE switch allows the integrator to have complete control of operation, power management, monitoring, scheduling and diagnostics— either locally or through remote access. Some switches can detect if an IP camera locks up and will remotely power cycle PoE to reboot the camera, eliminating a service call for the event. If the condition continues to reoccur, the switch can send an email notification to the integrator that service may be required. Add an uninterruptable power supply (UPS) to power the PoE switch in the event of a power failure, and you have a resilient IP surveillance system to offer your customer. This helps maximize profits on any service agreements in place.

Future Standards

As the industry continues to change, so does its demand for more power. Reports estimate that there will be 125 million PoE ports by 2017, with many devices exceeding the current 2009 standards.

Some vendors are already experimenting and offering PoE products providing up to 60 watts of power. This is accomplished by utilizing all four pairs in a Category 5e cable, which is currently not supported by the 2009 standard. However, choosing products that adhere to the IEEE standards can help minimize potential issues.

The IEEE committee is working on its next standard—intended to inject up to 60W of power with an available 49W of power at the endpoint. This will address the need for higher power as more uses for PoE technology to remotely power various devices are created. This extra power will come from tested and standards-approved use of all four pairs in a Category 5e cable; but, to minimize the heat generated by this extra power, Category 6 cabling may be required.

This article originally appeared in the September 2014 issue of Security Today.

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