The top differentiator of cables is what they are made of. The three most common elements are copper, plastic, and glass. All cables that conduct electricity are made of copper. Cables that conduct light are called “fiber-optic cables” and made of either plastic or glass. Plastic fiber-optic cables are used for short distances (under a mile or so) and longer distances are handled by “single-mode” fiber-optic cables, which are made of glass.

The National Electric Code (NEC) Article 725.21(B) has established three primary classes of wiring for cables inside buildings: Class 1, Class 2, and Class 3. Wiring Classes are determined according to the safety requirements of the circuits they serve.

Class 1 wiring is for powered devices requiring normal (mains) power or 120 V AC, actually, all wiring above 70.7 and up to 600 V. Class 1 wiring also includes low-voltage, low-current wiring that is essential for the safety of the building, such as boiler control wiring. For commercial buildings, Class 1 circuits must be installed within raceways, conduits, and enclosures for splices and terminations.

Class 2 wiring is low voltage and low power, typically not more than 30 V and less than 100 volt/amps (VA) power on the circuit. These are specifically for Communication and Signaling Circuits. Class 2 circuits are limited power circuits to protect against fire by limiting the power on the circuit to less than 100VA. Class 2 wiring also includes voltages from 30 to 150 V where the circuits are limited to 0.5VA, which also includes Ethernet and low-voltage alarm wiring as well as microphone and line level audio wiring.

Class 3 wiring includes circuits over 30 V and exceeding 0.5VA, but not more than 100VA, which includes background music system loudspeaker wiring such as 70.7 V wiring schemes. It also includes Nurse Call systems, Intercom Systems, and most Security Systems wiring. Higher levels of voltage and current are permitted for Class 3 systems than for Class 2 systems.

It is all about voltage and power. Anything that powers directly from 120 V systems is Class 1 wiring. Low-voltage systems can be either Class 2 or Class 3 wiring. Regarding power, a 12VDC circuit is considered Class 2 wiring if it is supplying below 0.5VA and is Class 1 wiring if it is supplying more than 100VA.

Wires are available in a variety of thicknesses called gauges (Figure 23.1). They are classified depending on how much power they must carry; the larger the gauge number, the smaller the cross-sectional area of the wire. Standard wire gauges include:

Cable insulation is rated for voltage and application.

Cables are also available as either solid core or stranded core. Solid core wire consists of a single piece of metal wire, whereas stranded wire is composed of a bundle of small gauge wires that are all twisted together to form a single, larger conductor. Solid core cables are used to power most devices that are powered from line power (120 or 220VAC). Solid core wires can also be used in Class 2 and Class 3 circuits.

Stranded wire is more flexible than solid core wire; however, solid core wire is more likely to maintain its shape when bent. It is better to use where there may be repeated bending or where more flexibility is needed. For example, stranded wire would be used in an Elevator Traveling Cable, whereas you could use solid core wire inside a conduit.

Stranded wire has a higher resistance than a solid core wire of the same wire gauge because less of the cross-sectional area is copper than solid core wire and there are unavoidable gaps between the strands of wire. Stranded wire is also more expensive to manufacture than solid core wire.

It is common to use cable colors to designate the purpose of the cable in installations. There are no color standards for communications and security wiring, but color standards do exist for fire, network, and fiber-optic cables. Fire cables are always red. For construction projects red should be reserved exclusively for fire cables.

For network cables the following colors usually apply:

Other colors may be selected to denote a difference between 100BaseT, 1,000BaseT, and 10,000BaseT wiring.

Fiber-optic Cable Colors:

Basic Cable Colors:

Security System Cables may be colored to denote system (Alarm/Access Control, Digital Video, or Intercom) and function (Power Supply cable vs. Analog or Data Cable). There are no standards for security wiring, so it is often helpful to designate specific cable colors to help delineate security from other cables in the building.

Cables are a bit like tires. There is an endless list of manufacturers. There are a few trusted brands that have withstood the test of time and countless others that you may have never heard of before. I recommend against buying cable from “Joe's Pool Hall, Used Cars, Yard Work, and Cables.” Early in my career I was supervising a project where the contractor had used off-brand cable “to save money.” There was one 3″ conduit with a very long cable run between two buildings. This conduit was packed to its legal capacity with wiring. Just to make things worse, the Electrical Contractor decided to coordinate this last remaining conduit between buildings between several low-voltage services, so there were three different contractors all sharing the same conduit. One of the security system cables did not work.

There was no continuity on this one wire between the buildings. There was also no more room to pull another cable. After two weeks of fruitless troubleshooting and struggling to find another way, the Electrical Contractor pulled all the cables out of the conduit. We isolated the bad cable and pulled all the cables back in, replacing the bad cable for a new one.

When the bad cable was examined, it was found that there was a strange lump in the middle of the cable run. We opened up the outer sheath and were astonished to find that the ends of two pairs of cable were tied together and these were run through the sheathing machine. No wonder there was no continuity from end to end. This one sheath held two separate cable runs, completely unconnected together. From that time until now, I have always specified either Belden or WestPenn wiring, both of which have always proven to be very reliable. More money has been lost in the name of saving money than any other thing.

Conduit has only one purpose: to protect the wiring that is within it. Without conduit, wiring is exposed directly to the elements and environment. This means that every time some yahoo sticks his head above the ceiling and pokes around, tugging and pulling on wires to see what's up there, he is tugging and pulling on your cable unless it is enclosed within conduit. When he tugs, he may dislodge a connection. He will never know; he will never care. You will get a call the next day to come fix a problem and after ten hours of troubleshooting, you will find a loose connection in a junction box. You ask yourself, “How did that happen?” You will never know. Just one of those things, you say.

Conduits make for more reliable security systems.

There are seemingly endless types of conduit available. These include²:

The question is not when conduits are recommended; they are always recommended.

Conduit should always be used outdoors. Outdoor conduit must be installed in a water-resistant or waterproof fashion; for example, making all entries to boxes from below rather than on the sides or top where water could enter. Liquid-tight flexible conduits should be used wherever the conduit may come in direct contact with rain. All connections should be properly sealed from the weather.

You can use cable without conduit in any of the following conditions:

NEC 300.17 has standards for how much you can fill up a conduit with cabling. It is important to know what size conduit to use for a given assortment of cables. For this discussion, we will examine Class 2 and Class 3 cables (Article 725). Different rules apply for Fiber-optic cables. Here are the rules:

This makes sense because one wire is easier to pull than two or more. And it is the total diameter of two cables, not their total cross-sectional area, that limits the amount you can pull. With three or more cables, it is the cross-sectional area that limits the amount of cables you can pull through the conduit.

Local Authorities Having Jurisdiction may down-rate these figures, so be sure to check before ordering conduit.

There are numerous tables and calculators on the Internet to help with conduit fill calculations, but I am going to give you the actual formula (for a single size of cable).

Here is the formula for multiple cable sizes within the same conduit:

You can make a handy Microsoft Excel spreadsheet to calculate complex quantities of different cable sizes for each conduit by following these steps:

Do not exceed 180 degrees of total bends in any single run of conduit. Doing so is a sure way to create conduit pulling problems.

The jacket (sheath) of a cable is a source of fuel for fires within buildings. Fires can be limited by using plenum rated cables that are designed to withstand direct contact with heat and fire.

All cables that transit through a wall, floor, or ceiling from one fire space to another should do so through an entry-way that is packed with passive fire-resistant material (called “fire-stop”). Fire-stop is available in intumescents (which expand when exposed to heat), mortar, silicone foam, caulking, fibers, and pillows.

Cable pulling is one of the worst jobs in a project. Pulling cable through conduit is much easier than running cable without conduit because there are no obstructions in the way of the pull. Every installer has stories about nightmares pulling cables. Most of the horror stories revolve around unconduited cables. The others mostly revolve around older conduits that have a break somewhere midpoint that do not allow a new cable to be pulled, even though there is plenty of space in the conduit.

Before you have been in the security system industry very long you will certainly see what is commonly referred to as a “Rats Nest” cable installation. These are installations where the installer just did not care. If it is your unenviable job to sort out this tangle of cables or add, modify, or troubleshoot a Rats Nest, your troubles have just begun.

Good cable handling is a blessing. Bad cable handling is a curse on everyone.

Cables should be pulled neatly into conduits and never subjected to tension beyond their rated tensile strength. They should never be yanked, jerked, or connected to a 4-wheel drive truck with tires over 45 inches driven by a man named “Bubba.”

All conduits should be equipped with a 200 pound test pull string that should be labeled with a number to easily identify which one to pull from both ends. Where there is no pull string you can use a fish tape.

All cables should be lubricated with an approved cable lubricant before pulling. Cables should be pulled through by the pull string, which should be attached firmly to the cables. The string should be bent back onto itself to create a loop and that loop should be tied off to itself. Cables should be fitted into the loop and twisted back. The twisted back portions should be tied back with phasing tape. This entire bundle should be coated with cable-pulling lubricant.

Make sure that all conduit ends are fitted with bushed chase nipples and de-burred to prevent sharp ends from damaging the cable sheaths.

Cable Dressing is the art of installing cables into enclosures so that they are neatly organized. Good Cable Dressing promotes better operation due to reduced cable and circuit interference and better maintenance due to the ability to find and add, modify, and delete cables.

Good Cable Dressing is a beauty to behold (Figure 23.2).

Remember the Rats Nest? When you encounter one, you will want to send a nasty message to the thoughtless fool who left you with the mess to clean up (Figure 23.3). Encountering a poorly dressed cabinet or equipment rack can add many unnecessary hours to a project.

Poor Cable Dressing virtually ensures system problems. With poorly dressed installations, technicians must tug and pull on cables to find out which one goes where. This invariably pulls connections loose that fail right then or much later. Poor Cable Dressing ensures that installers and technicians must spend countless additional hours to find circuits. It also adds many dozens of hours to a security system designer's work to figure out which old circuits to interface with and where those circuits are.

Cable Dressing is the art of forming and wrapping cables into neat bundles. Here are some basic rules:

Just as a “cross-dressing” man may look “a little odd,” so too do “cross-dressed” cables. Alert designers, installers, and maintenance technicians may look into an equipment rack or cabinet that on first appearance seems like a work of art, only to discover that it holds its own nightmares.

The most common is the bundling of Class 1 and Class 2/3 cables together. This is a no-no. Class 1 cables create a significant magnetic current around them that can conduct power directly into nearby Class 2/3 cables, causing system instability and even equipment damage.

The second problem I have seen is fiber-optic cables that are installed with radiuses that are too tight for the fiber. This can cause bandwidth limitations (again poor system performance) and even total failure of fibers as they age.

Similarly, it is not uncommon to see Cable Dressing addressed as a complete afterthought. The result of this is that the installer must pull cables so tight that their connections are under constant tension, and may ultimately fail in the field in operation.

All of these poor cable practices are certain to bring the maintenance tech back again and again and make the system owner more unhappy with each trip to resolve the problems.

Cable Documentation is the recording of all cables in the system including:

Cables can be documented on drawings or on schedules (tables).

The short answer is virtually everyone who cares about the reliable operation of the system. This list includes:

Cable Documentation should begin with the original design. Every decision about how to run cables, terminate cables, which cables to use, what terminations to use, and which colors and wire numbers to use are all engineering decisions. These decisions are made by a qualified engineer or they are made by a guy with a screwdriver in his hand.

You cannot buy a more expensive engineer than a guy with a screwdriver, because he must make each decision independently, devoid of knowing what all the other guys with screwdrivers on the job are doing and how they are doing it. Will he use the same cable, the same wire numbering scheme, the same connectors, and the same power supplies? No. The installation will be a mishmash of helter-skelter decisions, none tied to any single design strategy. In short, it will be a mess.

There are two ways to document cabling: Drawings and Cable Schedules (spreadsheets). Although both work, drawings are the best because they provide the most information. Cable schedules can “fill in the blanks” that drawings cannot, such as what color conductors to use on each type of terminal and so forth.

Cable documentation should be presented in the form of “As-Built” diagrams. Each cabinet or rack should have associated drawings in an envelope on the inside of its door. Each envelope should contain at a minimum: