Jim Montague is the executive editor for Control. Email him at [email protected].
Power over Ethernet (PoE). Sounds like a two-for-one sale, right? Well, in many ways it is, but just like any great deal, PoE has a few drawbacks, too. It evolved from a grab bag of proprietary technologies with different power levels and specifications, and it was defined in the IEEE 802.3af standard released in 2003, which was updated as IEEE 802.3at in 2009.
"PoE has been around for a long time, and everyone had their own proprietary methods before there were standards," says Tom Hajjar, vice president of R&D at L-Com, which supplies radios, surge protectors for PoE, injectors and switches. "This is why most of the market is still non-compliant. We make products for everyone, but we also comply with the PoE standards, so users can have products from different manufacturers work together safely. Most of the world is going with IEEE 802.3af and 802.3at, but non-compliant, proprietary PoE isn't going away anytime soon."
Larry Komarek, Ethernet product manager at Phoenix Contact, says, "PoE has been growing, but IEEE 802.3af only delivers a maximum of 15 W, which limits it mostly to security cameras and wireless access points. However, IEEE 802.3at provides 24 W at the end of a 100-meter cable and up to 34 W at the source, so it can power more devices, such as barcode readers, IP scanners and machine-vision inspection equipment."
To deliver more power and enable more devices, Komarek explains that IEEE set up a study group in April 2013 to investigate how PoE can deliver electricity over all four pairs of wires in typical Cat 5e and Cat 6 Ethernet cabling, instead of continuing to be limited to the two pairs that it used for power up to now. Phoenix Contact has offered PoE options for its managed Ethernet switches for a while, such as a module that plugs into the switch's backplane along with its midspan injector. However, it's also just introduced an unmanaged PoE switch that runs on 24 W and complies with 802.3at.
"We also see more distributed devices, intelligent sensors and integrated circuits with lower power draws, and they can use PoE as well," Komarek adds. "And, more managed and unmanaged Ethernet switches have embedded PoE, so they no longer need midspan injectors."
Shane Duffy, fiber and telecommunications product manager at B&B Electronics, explains that less-costly microprocessors and more-reliable power supplies provide more options for deploying PoE. These include switches with dual-power supplies, cleaner power for cameras, or managed switches with added intelligence that can deliver alerts on their condition or imminent failure. B&B makes managed and unmanaged PoE switches, including its Giga-Mini/Mc fiber-to-Ethernet switches, which are unmanaged, but still have some added logic for monitoring a fiberoptic link, and independently resetting its PoE if that link goes down.
"Besides being simpler to install due to fewer power supplies, PoE also means users don't need a battery backup for each connected device," Duffy says. "PoE only needs a battery backup or UPS for its central power supply."
Still, Duffy confirms that many users and developers also want IEEE 802.3at to move up to deliver 60 W, which is offered by some proprietary, non-standard components and suppliers. "If they've got outside heaters, illumination or other auxiliary devices, they want more power. Developers also are going from 2.4 GHz to 5 GHz, and putting multiple radios in one device, but they need stronger and denser signals," Duffy adds. "So far, there are two ways to get to 60 W — putting more than 30 W on the first two pairs of wires, which isn't approved by the standards bodies, or putting 30 W on the second two pairs. So, PoE's next step is standardizing a 60-W output, but the hurdle is handling heat on the wire."
Mike Hannah, marketing manager for networks and security at Rockwell Automation, adds that some users even want to get PoE up to 95 W. "This means PoE could start to drive I/O blocks on machines and even some controllers and HMIs," Hannah says.
Rockwell Automation is scheduled to launch its Stratix 8000 modular, managed Ethernet switches with four or eight PoE ports this summer, and it plans to expand its Stratix 5700 managed switch family with a fixed port at lower cost later in the fall. Both of these switches support the IEEE 802.3af and IEEE 802.3at standards.
"As the number of intelligent devices on Ethernet in automation continues to increase — for example, in process instrumenation — users can employ PoE for data and power, which helps simplify the design and deployment of systems," adds Hannah.