Last month we left off describing video cabling and installation. This month we will continue covering installation, going a little deeper into cabling design. We will then examine the design characteristics of the installed CCTV system.
SURGE SUPPRESSORS
While not required by the National Electrical Code, surge suppressors are a practical necessity for virtually all outdoor runs of coaxial cable. Since the pieces of equipment connected to these cables are very sensitive, they are easily damaged by voltage spikes. The most commonly used type of surge suppressors for communications circuits is metal oxide varistors (MOVs). Typically called protectors, MOVs are made of zincoxide particles pressed into a wafer and equipped with connecting leads or terminals. This device has a more gradual clamping action than either spark-gap arrestors or gas tubes. As the surge voltages increase, MOVs conduct more heavily and provide clamping action. And unlike spark-gap arrestors and gas tubes, they absorb energy during surges. They also tend to wear out over time.
INDOOR CIRCUITS
Coaxial cables indoors are subject to the following requirements:
-
They must be kept away from power or Class 1 circuits, unless the circuits are in a raceway, metal sheathed cables or UF (underground feeder) cables.
-
They can be run in the same raceway (or enclosure) with Class 2 or 3 circuits, power-limited fire protective signaling circuits, communications circuits or optical cables.
-
They may not be run in the same raceway or enclosure with Class 1 or power conductors. Exceptions are made if there are permanent dividers in the raceway or enclosure, or in junction boxes used solely as power feeds to the cables.
-
They are allowed to be run in the same shaft as power and Class 1 conductors, but in these cases, they must remain at least 2 in. away. (But, as noted above, this applies to open conductors, not to conductors in raceways, metal sheathed cables or UF cables.)
CABLE TYPES
The NEC goes into great detail on designated cable types. Many of these requirements apply more to the cable manufacturer than to the installer. Nonetheless, the proper cable type must be installed. The NEC designations and their uses are as follows:
Type CATVP
CATVP is plenum cable (hence the “P” designation), and may be used in plenums, ducts or other spaces for environmental air.
Type CATVR
CATVR is riser cable, and is made suitable (extremely fire resistant) for installation in shafts or from floor to floor in buildings.
Type CATV
CATV is general use cable. It can be used in almost any location, except for risers and plenums.
Type CATVX
CATVX is a limited use cable, and is allowed only in dwellings and in raceways.
You will find in practice, that many coax cables are multiple-rated. In other words, their jacket is tested and suitable for several different applications. In such cases, they will be stamped with all of the applicable markings, such as CATV and CATVR.
You may also notice from this list that all the cable types start with “CATV.” Although you may think that the term refers to Cable Television, it instead refers to Community Antenna Television.
Trade designations generally refer to the cable's electrical characteristics; specifically, the impedance of the cable. This is why different cable types (RG59U, RG58U, etc.) should not be mixed, even though they appear to be virtually identical — they have differing levels of impedance, and mixing them may degrade system performance.
SUBSTITUTIONS
The Code defines a clear hierarchy for cable substitutions. The highest of the cable types is plenum cable — CATVP; it can be used anywhere at all. The next highest is riser cable — CATVR; it can be used anywhere, except in plenums. Third on the list is CATV, which can be used anywhere except in plenums or risers. Last is CATVX, which can be used only in dwellings and in raceways.
The NEC also permits multipurpose cables to be used for CATV work. But, as always, only plenum types of cables can be used in plenums, riser types in risers and so on. The formal listing is shown in Table 820-53.
COAXIAL CABLE
Sending television signals requires much more bandwidth than telephones do. When the technology was first developed, the only cable capable of carrying these high-speed signals with adequately low loss was coaxial cable, also called coax. Coax uses a central conductor surrounded by an insulator, then an outer conductive webbing called the shield, and finally a plastic jacket.
Video transmissions require the high-bandwidth capability of coaxial cable. It is the design of the cable, with the central conductor widely and evenly separated from the outer conductor that gives it the high bandwidth capability. In addition, the outer conductor acts to contain the signal inside the cable, reducing the emissions from the cable that cause interference in other electronics and the interference of other outside sources on the signal in the cable itself.
The signal in coax cable is a simple voltage. It can be introduced into the cable at either end or even in the middle, where it will be carried to both ends. In any application, it is important that the transmitters be selected to be appropriate to the characteristics of the coax cable and both ends must be terminated to prevent reflections that can cause interference.
Coax cable must be installed with care. It should not be stretched or kinked. Doing so will reduce the level of bandwidth it will transmit. Connectors should be carefully installed to prevent signal leakage (the TV term analogous for signal loss) and unused ends must be properly terminated to prevent reflections.
CCTV USE
Of all types of security equipment, closed circuit television surveillance is currently the most often purchased, and it is the most often “planned purchase” in the next year.
The technologies that drive the demand for CCTV are:
-
Greater light-sensitivity for low-light surveillance at less cost
-
Improved picture performance
-
Better camera resolution
-
Better signal transmission, with lower costs, closer refresh/update rates and emergence of networked video and easier installation.
Median purchase retail price expected over the next year is $45,000; the average system planned in the next year is $215,000. Most likely because they specify systems for multiple clients, security consulting and architect/engineering firms, have the highest average CCTV sale: $533,000.
CCTV monitors will be the second largest planned purchase overall, 57% — and it's the number one choice of educators. Time-lapse video recorders are the third most purchased CCTV — top among financial service firms. In terms of CCTV transmission and signaling — 43% plan a purchase in the next year and the gap between fiber-optic and coaxial cable is closing: 25% and 30% respectively.
THE HUMAN FACTOR
From a technical standpoint, video monitoring offers great benefits, which is used for so many security applications. But there's a downside: invading human privacy.
Imagine working at your desk with an intimidating, intrusive video camera pointing at you all day. The camera makes many people feel vulnerable and mistrusted; it increases people's anxiety, reducing their happiness and their efficiency. Conceivably, being under constant surveillance could drive a marginal person over the edge — and into the very kind of actions we are trying to avoid in the first place. Finally, the camera subtly informs people that their individual virtues will not differentiate them from anyone else. After all, you are spying on them based upon the action of the potentially worst people.
You can do several things to minimize the human costs of surveillance. Among them are the following:
-
Look for alternative methods of accomplishing the same functions. For example, monitoring doorways only might accomplish your goal, without making people feel that they are always being watched.
-
Make sure to explain your decision to use video surveillance to every person that will be affected.
-
Explain to all personnel how the new security measures are designed for their safety. Give them details as to how the system was designed, how it operates, and how it will keep them much safer. In a short time most of your community will know that your facility is very well protected.
-
Develop a very explicit policy on how the videotapes will be used. For example, they should be seen only by one or two security people; they should be reviewed for security purposes only (no spying to see who takes an overly-long coffee break); and they will be destroyed after 30 days, unless there is a security-based reason to preserve them.
-
Keep your policy to the letter. No cheating. If you break policy and use the tapes for other than the stated reasons, people will find out.
-
Keep track of how your people feel about the video monitoring. Do they feel like it is keeping them safer? Or do they feel like slaves under the watchful eye of big brother?
Remember that you have a lot to lose from video monitoring. Happy people make money for the company; unhappy people will lose money and will ultimately drive a company out of business. And who wants to work in unhappy place anyway?