The Powers That Be
When we plug in a device we expect it to turn on and work for some period of time. That may have been fine with our traditional analog devices when, as long as we had enough dedicated circuits available, we plugged stuff in and off we went.
But life is not that simple in the datacenter world. Let’s take a look at power, an area we need to consider more seriously than ever before.
Outages Make Devices Say, ‘Ouch!’
It’s likely you’ve experienced blackouts and brownouts at one time or another. For us, they are inconvenient; for electronic equipment, they can be deadly.
Blackouts are a total loss of power to a location or area. The problem is not so much when the power goes out as it is the surge that occurs when the power comes back on. That is a big threat to our equipment.
Brownouts — voltage drops below normal minimum levels — happen so frequently we often don’t notice them. Brownouts also happen in three-phase systems when one phase drops out. 
Brownouts tend to cause more damage than blackouts. Their frequency and the way they starve devices for voltage can create more significant problems.
Both of these issues can be mitigated with the use of a power conditioning device. Often built into a good UPS (uninterruptible power supply), these simple devices can save you many headaches by utilizing circuitry to smooth out the power sine waves and provide a good, clean power source. (Not to be confused with the common surge protector found in consumer-grade power strips, which merely pop a breaker when the voltage or current rises.)
Mad With Power
Another common problem we run into is not having enough power available to us. If you are going to run a single DVR or small camera power supply, the common household 15A circuit may be just fine.
If, however, you are installing a larger system, with multiple DVR/NVR/server combinations, camera power supplies and viewing stations, etc. you need a larger circuit. Generally, most equipment installations require one or more dedicated 20A circuits. You don’t want the coffee maker next door in the break room knocking your system offline.
When you design the system, you need to do the power calculations upfront. Even if the room itself is already in place, you need to know your power requirements and what is available. You need to figure out the number of devices, and how much power each device needs.
Don’t Get Left in the Dark
So, what happens when the power does go out? The cameras won’t have much of a problem with it, as they can take the hit … but what about the head-end devices?
PC- and other CPU-based devices don’t like to be shut down unannounced. They each have their own shutdown procedure, and they can get grumpy if they get turned off improperly.
This is the real, and main, reason the UPS was developed. A UPS is not designed to keep your equipment running indefinitely during a power outage. It is there to give you enough time to either restore power, or shut the device down properly.
A UPS is not much more than a big box of batteries (OK, that’s oversimplifying it a little). These batteries are constantly being charged by the main’s voltage. As mentioned above, a good UPS will also have a power conditioning circuit, so it can provide clean power as well as battery backup.
Every system out there should be attached to a UPS. This should be one of the main considerations when designing an IP video system, especially with any digital recording devices. When a DVR or NVR (or any storage solution, really) captures video, it makes entries into a database of some kind.
This database keeps track of the locations of all the clips on the hard drives. When playback is requested, the system will refer to this database to reassemble video clips for viewing. Here’s a hot little tip … power outages corrupt databases! Even if all your video is stored on nice redundant disk array, a corrupt database will mean you can’t get to the video you need.
It’s true that in many cases the database can be rebuilt — but not always. This is a primary reason to be proactive and provide good quality backup systems on every installation.
The New Power Play
One of the new stars in the marketplace, and a direct result of the IP Convergence Wave, is PoE, or Power over Ethernet. PoE is really an example of one of the great benefits of an IP system. It gives you the ability to run a single Cat-5e/-6 cable out to a device, and get both Ethernet data and power to and from the device.
PoE has been common in VoIP (voice over IP) phones for some time now, and it is available on the vast majority of the IP cameras on the market. (There are some exceptions for outdoor, environmental housings and p/t/z cameras, as PoE can’t always supply the necessary current to run heaters, blowers, motors, etc.)
PoE is generally supplied by a network switch, although there are PoE injectors available if you have a switch that doesn’t offer it. These switches provide anywhere from 36-57VDC, but most devices use 48V. The 802.3af standard specifies a current draw of 10-400mA, and a maximum power load of about 15W. Care needs to be taken to avoid exceeding these limits and possibly damaging your switch hardware.
Not all PoE switches provide the power on all ports; there are usually a small number of ports that are PoE capable. You want to make sure your PoE devices utilize these ports. A non-PoE-capable device can be safely plugged into one of these ports if necessary. The switch will sense devices that do not require power (with the use of a resistor) and only power up if necessary.
One big thing to remember: PoE links observe the same distance limitations as standard Ethernet links. You are limited to 100m (328 feet). There are extenders available, however.
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