Can Your Building Access Control System Really Be Powered By PoE?
Will it deliver as promised?
Building owners and security system designers have looked with anticipation toward the day when a single network drop at the door will satisfy all of the wiring requirements for a building access control system. One simple cable that will replace the multitude of cables currently needed for card reader communications, request to exit, door position, and lock power. Power over Ethernet (PoE) has long been heralded as the answer to this quest.
As you might expect, along with technology that is new to the security industry comes advertising claims and counter claims by various vendors each vying for a prominent spot at the top of the tech-tree. Being familiar with the relevant standards can help you sort through the marketing hype and determine if PoE is a viable solution for your application.
Relevant Standards
PoE - IEEE P802.3af - 2003f: Since 2003 the applicable IEEE standard for PoE has been P802.3af. This standard calls for a maximum allowable 12.95 watts of power per port and allows the use of CAT 3 cable. As PoE has become more popular, more and more devices have been designed for its use. The power limitation of this standard has stifled the device manufacturers ability to meet the demands of the marketplace.
PoE Plus - IEEE P802.3at (coming soon): The new PoE Plus (or Hi PoE) standard is nearing completion and is expected to be ratified soon. IEEE P802.3at devices have a maximum wattage requirement of up to 25.5W, nearly twice the power allowed under the AF standard. Switch manufacturers are already producing switches that conform to this standard, at least to the extent that they can anticipate the final standard’s requirements. It is important to note that PoE Plus requires the use of Cat 5 (or better) cable. The eight wires of CAT 5 cable verses the four wires of CAT 3 allows more power to be transmitted.
One objective of the IEEE P802.3at Task Force was to ensure that PoE Plus will operate in modes compatible with existing requirements of IEEE P802.3af. This is good news for forward thinking companies that have already made a significant investment in powered devices designed to the older standard. Another objective of the Task Force requires PoE Plus powered devices, which require PoE Plus power sourcing equipment to provide an active indication of that requirement when connected. This will alleviate the inevitable problems caused by connecting powered devices designed to the new AT standard to power sourcing equipment that complies only with the older AF standard. Conversely, PoE Plus powered devices that operate within the more limited power range of P802.3af will work properly with 802.3af power sourcing equipment.
Back-up Power
One of the biggest advantages offered by the PoE infrastructure is the inherent ability to facilitate system wide power back-up. If your system is PoE based, then backing up power for the entire system is simplified. Employing an emergency generator or a network UPS will ensure that the access control system continues to be fully functional during a power outage. Legacy systems typically employ battery back-up techniques that fail to provide sufficient power for critical components such as door locks or request to exit devices.
Power Sharing
An important concept to recognize when considering the deployment of a PoE network is that of power sharing. This concept has largely been ignored by PoE marketeers. Simply stated, power sharing is when the total power available from power sourcing equipment is shared across all of the available ports. So if the power sourcing equipment delivers 12.95W of power and 9 or 10 watts are required on each port, your equipment will only power one port. The slight of hand that the industry marketing fails to acknowledge is that yes, while you can power your access control system with older IEEE P802.3af power sourcing equipment, they don’t tell you that you’ll need a switch for every access control door in the system. This is not an economically feasible solution. Not every pre-IEEE P802.3at switch employs the power sharing principle, but it is something that any potential PoE system user needs to be wary of.
Today’s newer switches do not utilize this methodology. Each port can be configured by the operator to deliver a specific class of power. This ensures that your purchase of an 8 port switch will enable you to power the devices required at eight different doors if needed.
Conclusion
PoE is quickly becoming a viable alternative for access control system designs. Network switch manufacturers are producing power sourcing equipment designed specifically for the security industry and access control manufacturers offer PoE capable powered devices for their access control systems.
Well designed PoE based access control systems will:
1.) Utilize power sourcing equipment that avoids power sharing across the various PoE ports of the device.
2.) Comply with the new IEEE P802.3at standard including CAT 5 or better cable and Hi PoE power availability.
3.) Incorporate a cascading technique that employs smaller switches in a distributed architecture.
4.) Consist of powered devices that have been designed and tested to meet the PoE Plus standard.
5.) Incorporate power back-up systems that keep the access control functioning during a power failure.
6.) Have built-in protection features that help your security system stay secure.
The long awaited panacea for access control systems may very well be a reality soon, thanks to the new, soon to be ratified, IEEE P802.3at Power Over Ethernet specification. Be careful when looking through the marketing hype and identify those access control system and PoE device manufacturers that understand and conform to the developing industry standards. Remember that just because a technology can be demonstrated on the show floor at an industry convention does not necessarily mean that it is mature enough to be practical.
