1.2 Types of Cables

Basics​

Even though you may have wireless devices on your network, your building or campus network is going to rely on physical cables. Following structured cabling practices, you can wrangle and organize all of those cables to make your job easier and more efficient. Cables come in different types for different uses.

You should know the following terms:

  • Plenum
  • CMP cables (CoMmunications Plenum)
  • PVC (Polyvinyl Chloride)
  • Non-plenum cables
  • Communications Multipurpose Riser (CMR) cables
  • Riser cables
  • Backbone cabling
  • Communications Multipurpose cables (PVC CM cables)
  • Twisted Pair cables
  • Shielding
  • Multi-mode fiber
  • Single-mode fiber
  • Outdoor cables

Following is a general description of the types of cables, their uses, and where they are used. 

  • Plenum cables reside in plenum spaces.  Plenum refers to space in a building with open airflow circulation, like between a drop ceiling and ceiling or within a raised floor. Air flows freely in these areas and that air circulates around your end users. In the case of a fire, cables used in a plenum area must be more fire resistant and produce no toxic fumes if they are burned. Plenum cables are also referred to as CMP cables, an acronym for CoMmunications Plenum, and are coated with Teflon for higher safety ratings. Because of this, plenum cables are often more expensive. 
  • Non-plenum cables reside in non-plenum spaces. Non-Plenum spaces have air ducts that encapsulate the air-users are not freely exposed to the air that is circulated. The outer jackets of these cables are made of PVC (Polyvinyl Chloride) and they do not have the added Teflon coating. Non-plenum cables are not fire resistant and can produce toxic chemicals if they are burned.
  • Communications Multipurpose Riser (CMR) cables, often just called riser cables, are installed vertically between floors through conduit or a shaft that encloses it; the conduit is intended to prevent fires from spreading from one floor to the next. Backbone Cabling often goes between floors so would require riser cabling. They should not be used in place of plenum cables.
  • Communications Multipurpose cables (PVC CM cables) are used to connect devices in a Work Area to a wall jack. These cables meet the lowest safety standards.

ANSI Standards

The ANSI standards helped to categorize cables. This led to the familiar “Cat” description. You may still have Cat5 cable, but Cat6 and Cat6a may be more common at this time. There are also Cat7 and Cat8 cables but may not be found as often. It’s likely the “Cat” categories will continue to evolve over time. Each “Cat”egory is suited for different uses, so you should pick the right cable for your intended use.

UTP versus STP

These cable types are somewhat similar, with the TP in their names referring to twisted pair cables. The S versus the U is the important decision. The S in STP refers to shielding. In an STP cable, the twisted pairs of wires are wrapped in metal and then have an extra layer of wrapping for extra protection. UTP cables are only wrapped once with no metal wrapping. UTP cables tend to be less expensive than STP cables. 

In some situations, shielded cables are preferred over unshielded cables despite the additional cost. Review the following table for uses of STP versus UTP cables and check out some of the additional resources.

Using STP vs UTP Cables

When to use STP Cables

When to use UTP Cables

 

  • To avoid electronic or radio interference from places such as high voltage closets, airports, factories, radio stations, or some appliances.
  • In security systems
  • To avoid “crosstalk,” which can occur when a lot of cables are close together.
  • When you have the time to install it and ground it correctly.

 

  • Office LANS
  • When large bandwidth is not a requirement
  • If budget is a concern and you can avoid some of the issues STP cables resolve, like interference.
  • If you need to save weight or space, as UTP cables are lighter and more compact.

Fiber Optic Cables

You may have some cables in your network that transmit data packets using fiber optics. These cables rely on transmitting information using light rather than electrical signals. Fiber optics can transmit information over longer distances without the signal degrading and it is not influenced by radio frequency interference. They are very difficult to monitor. Fiber optic cables have different layers that protect the internal core and prevent the light from reflecting back into the cable’s core and interfering with the data being transmitted. The color of the outer protective coating is used to designate the type of fiber inside the cable.

Multi-mode fiber often uses an inexpensive light source, like an LED, and is colored either orange or light blue. This type of cable is usually used for short-range communications but can transmit data up to 10 miles.

Single-mode fiber uses a stronger light source, often a laser, and can transmit data much further--over 60 miles. The outer coating is usually yellow. Obviously, single-mode fiber is often more expensive than multi-mode fiber.

Outdoor Cables

Outdoor cables provide options for protection to meet the needs of different outdoor environments. The most basic is protecting the cable from water, sunlight, and temperature changes. Some other considerations you may have include whether you need to protect the cables from rodents or other animals and whether the cable has to be buried. Burying cables may require running the cable through conduit unless you purchase cables that can withstand outdoor elements. Never use indoor cable for outdoor settings.

Choosing the Right Cable

You need to select the right cable for the job. There should be no more than 100 meters of cabling between a switch and a computer for a Gigabit Ethernet link using twisted pair cabling. That's 328 feet. There's also a difference between solid and stranded cabling.

Solid cabling uses a single thick wire for each conductor and is used for more permanent links, like cable that is run through walls. Solid cabling may also be called drop cable. Installers drop the cable through the wall to the hole in the wall where the wall plate is going to be installed. Solid cables are connected to the back of the wall plate with Insulation Displacement Connectors (IDC) rather than RJ-45 connectors.
 

Table with cable information

Here are additional resources you may find useful:

Complete the following task or self-assessment:

Start with a wiring closet and identify the types of cables and their uses. Also visit other areas of your facility, including having a look outside, to answer the following:

  • What are the different types of cables found in your building/campus?
  • Where do you find UTP versus STP cables and fiber optic cables?
  • Did you find any cabling that is more than 100 meters between a switch and a computer?
  • What does a review of the outside of your building reveal?
  • Do you notice any areas of wear or other issues?