The world of cables has many particulars. The engineering of a cable’s
electrical properties and it’s application is usually formost in a
consumer’s thoughts when looking to purchase a cable. What’s not as
frequently considered is the material used to insulate the cable. This is
known as the jacket. Most store-bought cables are expected to be used in a
home or office, but when buying cables for a more particular use the
materials used in construction become more of a concern. Do you want to run a
coax cable to your detached garage for a TV? Can you run a normal network
cable in the plenum space in your office building? Is it legal to send this
cable to my customer in Germany? We hope our answers to these questions, and
more, will help make your next project a lasting success.
The information printed on a cable jacket will usually tell you everything
you need to know. Typically this includes the manufacturer or UPC code,
jacket material, any electrical standards it meets, temperature rating, and
frequently a material rating that will tell you where the cable can be run in
a building. Let’s look at a common
Cat-6 network cable as an example.
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CM – This is the material class for the cable. This is an example of a UL rating. A detailed explanation of UL ratings is given below. CM means this cable is made for general purpose. If this specified CMP or CMR, the cable would be suited for plenum or riser applications.
24 AWG (American Wire Gauge) – The indiviudal conductors of this cable are 24 gauge. This does not indicate that the conductors are solid or stranded.
75 degrees Celsius – This does not mean that the cable will combust at this temperature, but rather the plastics used will slowly degrade if kept above this temperature for extended periods.
Underwriters Laboratories – This is a standards body that oversees the design and manufacture of all kinds of products. It is not part of any federal code requirements, but is sometimes required by some companies for insurance purposes.
The UL reference number relates to the manufacturer of this product.
Canadian Standards Association – This is another standards body like UL, but is obviously more specific to Canadian installations.
Just like the UL reference, the CSA reference number relates to the manufacturer.
CMG – This is the rating of the fire retardent in the cable.
Electrical Testing Laboratories – The standards body that verified this cable
Verified – Indicates that this cable was verified by the afore mentioned body.
TIA/EIA-568-b.2-1 – The coloring specification for the conductors inside this cable is in EIA-568-b revision 2-1 format. For network and phone cables, this lets you know which order to put the conductors in a crimp connector or to punch down to a block.
CAT.6 – This of course indicates that this is a Catagory 6 network cable. Were this a coax cable, it would specify an appropriate standard like RG6, RG59 or RG59.
Unshielded Twisted Pair – Twisted pair cables offer a simple form of shielding by twisting two conductors together down the length of the cable. The number of twists per inch (TPI) in networking cable is usually around 2 to 3 TPI, but this is up to the manufacturer. Catagory specifications like Cat 5 and Cat 6 do not define cable construction, only the electrical performance after manufacture. If this were shielded cable, this would say STP for Shielded Twisted Pair. Frequently cables will also specify the percentage of the shield. Coax cables can be anywhere from 60% to 99% shields, and frequently have several layers. Many satellite TV providers reccomend “Quad Shield RG6”.
While this information is rarely in the same order on different types of
cables, the material ratings have the same meaning.
The Acronym UL stands for “Underwriters Laboratory.” So what’s
this organization and what do they do? Underwriters Laboratory is an
independant organization that tests thousands of products under controlled
conditions. The goal is to determine in what applications these products are
safe to be used. The end result is recognizable standards (such as CM – see
above) that help consumers and businesses select products that they can
reliably count on for their specific applications. A few ratings that are
frequently encountered in cabling are:
14/2 (14AWG 2C) 105 Strand/0.16mm Speaker Cable CL3 Rated
22/4 (22AWG 4C) Stranded CM Security Cable
18/2 (18AWG 2C) Plenum Shielded Stranded CMP Security Cable, White
The material the jacket of the cable is made of is one of the most important
features in defining where the cable can and can’t be used. It’s
important not only in how physically durable the cable is but also how
resistant it is to things such as fires. Some examples of materials are:
One of the most important considerations you can make when choosing a cable
is selecting a cable with the appropriate shielding. If this decision is
neglected it could lead to a poor signal or no signal at all. The culprit is
electrical interference, electrical currents effect other nearby electrical
currents and in the world of electronics this leads to unwanted performance
degradation. The amount of shielding required will vary widely depending on
what type of cable you’re using but also your application. Examples of
when shielding decisions are necessary includes:
A Cat5 cable being used in your home vs. in a commercial server room.
A coxial cable being used in your living room vs. be run into your home with
your power cables.
Another example would be if you’re running a multimedia application over
something like Cat5/6.
In general whenever your cables are in close proximity to power cables a
shielded cable should be a consideration, especially when the cables are
running parallel to each other. Some examples of shielding include:
CAT6, STP (Shielded), 24AWG, Solid, 500MHz, Bulk Cable, Blue
RG6 18AWG, Solid Pure Copper Coaxial Cable, 95% Copper Braid
Cables such as coaxial cables have a dielectric insulator. The primary
responsibility of a dielectric insulator is to keep the wire in the center of
the cable as well as keeping a distance between the wire and anything that
may be able to cut or pierce the jacket. The dielectric insulator is usually
made of polyethylene or polytetrafluoroethylene. In Cat 5 / Cat 6 cables that
are shielded Mylar is used as an insulator. Mylar is a polyester film that is
extremely strong with excellent insulation properties.
A good picture of a
coaxial cable’s dielectric insulator
Outdoor Ratings/Direct Burial
Most cables are not inherently made to be used outdoors. A cable being
exposed outdoors presents a few challenges which, if not addressed in the
manufacturing of the cable, could lead to the long term failure of the cable.
It’s important to consider the following when looking at
RG59 Siamese Coaxial Cable, Solid + 18/2 Power, Outdoor / Direct Burial, Black
CAT5E, CMXT Outdoor / Direct Burial, Waterproof Tape
Questions and Answers: