Security Technology Executive

JUL-AUG 2018

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S-20 ACCESS CONTROL TRENDS AND TECHNOLOGY 2018 JULY/AUGUST What about IEEE 802.3at, or PoE- plus? This updated standard provides up to 25.5 W of power to compatible devices. Unfortunately, this standard was heavily discussed before it was actually adopted and released, and many different "non-standard" con- figurations were fielded in anticipation of what the standard might actually be. With only a couple of exceptions, nearly all current PoE access control systems are specified as 802.3af compliant, and it is wise to stay within those boundaries when calculating things like power budgets unless you know for certain the device and the PSE is 802.3at compliant. Advantages Now that we've laid out the basics, let's discuss the primary advantages of PoE. First, both data and power are carried along the same CAT5/6 Ether- net cable with standard RJ45 connec- tors. The voltage present on the actual cable is typically 48 VCD. This is low enough to be safe but high enough to supply the typical voltage and current to drive most of what is needed for a typical access control portal. Part of the standard discussed above also includes current monitoring so that if something is malfunctioning, the PSE will shut down power to that particular device and safety is maintained. Additionally, most network setups incorporate some level of central power backup (i.e. uninterruptible power supply, or UPS), so you are sav- ing on backup batteries and the associ- ated maintenance that goes with them. Another component of the standard is the utilization of power classifica- tion, where PDs provide an indication of how much power they require (this is classified in bands of 4, 7, and 13 watts), allowing for more efficient power allocation and savings. This also means that on more sophisticated equipment, a remote device, such as a door controller that is not function- ing correctly, can be power cycled and remotely reset without having to dispatch a field engineer to manually perform this function. Limitations First, there is the 300-meter cable length limitation. Though it's not a severe limitation and there are ways around it, it can be costly. Another limitation is the power budget of the PSE. For example, we learned early on that many inexpensive PoE switches have eight ports with a total power budget of 30 watts. For all intents and purposes, an access control door will require the entire 13 watts that 802.3af can supply. Devices like an Open Options NSC-100 with the full 13 watts of power available can supply 700 mA. of current downstream. Let's say we have a strike that requires 300 mA., a reader that needs 150 mA., and a motion detector as the request to exit device that needs 26 mA. With all this, we're bumping up to around 500 mA. Anything additional and we have consumed pretty much all the avail- able power. Given the eight ports with only 30 watts of power, we are only going to get what we need on a couple of ports, and the others aren't going to have enough power to power our por- tal. The seemingly obvious solution is to get a really expensive and sophis- ticated managed PoE switch with a full power budget. Unfortunately, this can work against you, too. Some of these switches will monitor the current consumption on the ports, and over a period of time, they will reduce the output on the port to the calculated average consumption. On a door that doesn't get used often, this can wreak havoc when the switch reduces the power to a level that won't support the current draw when the strike activates. This causes the device to be current- starved and the controller to reboot. In the end, it is simple. If you are utilizing PoE for access control, the managed switch needs to be pro- grammed to provide full power at all times, and all scheduled shutoffs need to be disabled. Be sure you are aware of how much power your PoE device can provide, as not all PoE door con- trollers deliver the same power output for downstream peripheral devices. Monitor your power budget and you will be fine. UL Listed Devices Earlier PoE access control controllers came with a carefully crafted dis- claimer that it could only be UL listed if it were powered by a UL 294 non-PoE power supply, because there were no UL (or more appropriately, Nationally Recognized Testing Laboratory) listed PoE power supplies in existence at that time. If you are required to have an NRTL listed system, be sure that you are incorporating listed PSE to power your PoE equipment. What About Life Safety? Unfortunately, life safety is an issue that is easier to deal with in the non- PoE world. Not only does it have the building codes behind it, but in most places, it carries the weight of the law as well. On one hand, this can be pretty simple – just have the fire alarm contractor install an addressable relay module at the door that needs over- ride, routes your lock power through it, and you are done. Do not make the mistake of think- ing that you can just program the access control system to unlock the door when it sees an input from the fire alarm system. Access control systems are not listed for this kind of service. This must be accomplished outside the system. Per NFPA 101 Life Safety Code Section Access- Controlled Egress Doors: "When oper- ated, the manual release device shall result in direct interruption of power to the lock – independent of the access With only a couple of exceptions, nearly all current PoE access control systems are specified as 802.3af compliant...

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