A Natural Choice: PoE

As network technology becomes increasingly important to operate security systems, and affordably priced Internet protocol (IP) cameras and video management systems (VMS) are used more often, system designers and installers, such as electrical contractors, are realizing the need and efficiency of using power over Ethernet (PoE).

First used for voice over IP (VoIP) telephones, PoE has gained popularity as a means of safely allowing power, along with data, to pass on Ethernet cabling.

“PoE voltage is 48V DC and sourced from an injector, midspan or switch, which provides power. A PoE source will only provide the necessary power when it recognizes the class or signature of a compatible network device so that, in the event a non-PoE IP device is inadvertently connected, the PoE source will not provide power and damage the device,” said Ronnie Pennington, national accounts manager for Altronix Corp., Brooklyn, N.Y.

From VoIP in the 1990s, PoE is now migrating to powering security system components, such as IP cameras and access control and sensor equipment.

“It’s a natural choice for the security market because it enables the user to leverage a common network infrastructure,” said Patrik Pettersson, product analyst for Axis Communications Inc., Boston.

It’s also more environmentally friendly because, if the device only needs 7 watts (W) to operate, the switch only allocates the required operating wattage, even though the original IEEE 802.3af 2003 PoE standard provides up to 15.2W of DC power to each device.

PoE benefits
“First and foremost, PoE standardizes the deployment of security system devices on one type of cabling infrastructure so that now only one Cat 5 or 6 data cable can be used for video transition, power to the product and control of the camera,” Pettersson said.

And because the network switch now also functions as the power supply, that switch can be protected by an uninterruptible power supply (UPS) battery backup.

“A power outage or other disaster is one of the most critical times for security and surveillance. With a proper disaster backup and recovery strategy, the end-user can keep the PoE-powered surveillance system running along with other critical applications,” he said.

Since the PoE cable is directly tied into the intelligent network system, the power supply also is now intelligent, enabling remote control of individual circuits and devices, diagnostics and maintenance capabilities, Pettersson said. Intelligent switches that enable the user to remotely toggle the power on and off provide the choice of when to reboot a device (if necessary while troubleshooting) for minimal impact to the security and surveillance system.

“It also eliminates the need for a truck and ladder to reach the camera for a physical reboot,” he said.

One of the challenges, however, of using PoE for security system power is the limitation of structured cabling to transmit beyond 100 meters, according to Pennington.

“IP data can be extended up to 600 meters using Ethernet repeaters, but installers and system integrators should take into consideration that there will be a voltage drop along the way,” he said.

While the data range can be efficiently extended using plug-and-play repeaters, the voltage, in that case, may be insufficient to power the device, and a local power source may be needed.

“Because of this, contractors need to perform proper power calculations and invest in PoE testing tools, which test both the power and data integrity of a multiple cable system,” Pettersson said.

Factors to consider
In choosing to use, specify or design PoE switches for a security system, it is important for contractors to select a switch that is compatible with the system’s edge devices’ power requirements and offers desired features, Pennington said.

“It is ideal to use a PoE midspan or injector with an external Ethernet switch, rather than an integrated PoE switch for security. If the PoE switch is shut down for maintenance or if power is lost, the surveillance system would be inoperable, but when using a PoE midspan or injector, power is still supplied,” he said.

Contractors also need to consider the power budget of the security system’s devices and perform power-draw calculations, which includes reading the PoE network switch manual and fully understanding the specifications.

“For example, if a 24 port is shipped with a 150W power supply and it offers PoE on all 24 ports, it will not support 15.4W per channel, as outlined by the current standard,” Pettersson said.

Moving forward, the IEEE 802.3at standard in development, also known as PoE+, will enable up to 50 or 55W sometime within the next three years.

“The standard is being driven upward by the more powerful security system devices that are being developed, even as those devices are becoming more energy-efficient,” Pettersson said.

BREMER, a freelance writer based in Solomons, Md., contributes frequently to ELECTRICAL CONTRACTOR. She can be reached at 410.394.6966 and darbremer@comcast.net.

About the Author

Darlene Bremer

Freelance Writer
Darlene Bremer, a freelance writer based in Solomons, Md., contributed frequently to ELECTRICAL CONTRACTOR until the end of 2015.

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