Monday, April 07, 2008

What type of coax cable should I use for my television?

First figure out what you're installing it for. If you're putting it in to run regular cable television (CATV) or master antenna television (MATV), you don't need coax with special sweep-testing. The signals from these types of inputs are very strong. If you're planning on using satellite television (SATV), however, you'll want to make sure that you use coax that has been sweep-tested to 3GHz as recommended by most satellite service providers.

In any of these cases, you want to use RG-6.

Then it comes down to the shielding. Coaxial cable has two types of shielding: a foil and a braid. A 40% braid is a loose braid and is the most economical. It is generally used in places like motels where getting perfect reception isn't terribly important because people will only be there for a night or two. A 60% braid is the standard braid for RG-6. Most professional installers use RG-6 with a 60% braid. Quadshield coaxial cable has two foils and two braids. RG-6 Quadshield is the premium choice for RG-6 and is used by most people who have the chance to choose the cable for their own systems.

The type of conductor in your coaxial cable will also be important. The two conductors you will find in coax are copper clad steel (CCS) or solid copper core (SCC). Copper clad steel will be suitable for most installations, but if you want the best signal possible, then you should look to purchase a cable that has a solid copper conductor. The stronger signal produced by a solid copper conductor is ideal when you are using a satellite signal or you are looking for the best signal for your HDTV. The copper clad steel conductor will work for both satellite and HDTV, but to make sure your signal is as strong as it could be, then use the solid copper conductor.

Another thing to look for is UL listing or ETL verification. This independent testing ensures that cable actually is what the seller or manufacturer claims that it is. There is a lot of bargain coax out there without any sort of independent testing mark, so you'll want to specifically ask about this before making a purchase.

Wednesday, April 02, 2008

What is the difference between CL2 and CL3?

CL2 is the designation for Class 2 Circuit wire and CL3 is the designation for Class 3 Circuit wire. Both are regulated under NEC Article 725. They are both used for remote-control, signaling, and power-limited circuits. In plain English that means that CL2 and CL3 are types of multi-purpose wire used for things like security systems, speaker wire, intercom systems, nurse call buttons, and more.

The difference between the two is that CL2 is rated for up to 150 volts while CL3 is rated for up to 300 volts. (NEC 725.71 F) According to NEC 725.2, CL2 offers some protection from electric shock while CL3 offers a bit more because it is rated to carry more voltage.

CL3 may be used in place of CL2, but not the other way around.

What is Cat 6e or Cat 7?

As far as TIA (Telecommunications Industry Association) standards go, Cat 6e and Cat 7 do not exist. Standards for Cat 6e or Cat 7 have not been approved by TIA; therefore, Cat 6 is currently the highest TIA standard for twisted-pair communications cable (As of 3/02/2008).

If you see cable called "Cat 7 or Cat 6e" (or some other higher number), that is just a name that a company made up to put on their cable. One manufacturer's Cat 6e or Cat 7 could be built by totally different standards and specifications than another manufacturer's cable.

So, if you still want to pay the extra bucks to get Cat 6e or Cat 7, just know that you will be getting cable that could be made anyway the manufacturer feels like it. To me, your best bet is to go with Cat 6 cable, this way you can rest easy knowing that your cable is up to standards.

What is plenum cable?

"Plenum" is a fire code rating. It is sometimes identified by the designation "CMP" meaning a communications plenum rated cable.

Plenum cable has a jacket made of Teflon rather than PVC (which you will find on CM or CMR rated cable) and is used in spaces designated for air-handling, such as drop ceilings that conceal return air vents in office buildings. The Teflon gives off much less poisonous gas than PVC when it burns. Thus by using plenum cable in air-handling spaces one prevents poisonous gas from being created and spread throughout the building through the air ducts during a fire.

Many commercial installations require the use of plenum cable. To make certain you are installing cable that is up to code, you have to check with your local fire marshal or building inspector. The laws vary from state to state and town to town.

If you have a copy of the NEC (National Electrical Code) book, take a look at section 800.51 (A). This states that one test used to define CMP cable is the Standard Method of Test for Flame Travel and Smoke of Wire and Cables for Use in Air-Handling Spaces. You can also take a look at the UL July 2004 Cable Marking Guide (page 21 under CMP) to see the UL requirements for a CMP rating based on this test.

Tuesday, April 01, 2008

What is the difference between Cat 5e and Cat 6?

This is one of the most common questions we're asked. There are two major differences:

  • Signal to noise ratio

  • Bandwidth used to test the cable

The first difference is the most important. Cat 6 Cat 6 is twelve times less "noisy", than Cat 5e. When your computer sends data across your network some data packets are lost or corrupted along the way. These packets have to be resent by the system. The better the signal to noise ratio is on your network, the less often this happens.

As computer networks become faster, the signal to noise ratio becomes more important. If the network is racking up packets that must be resent faster than it can resend them, the network may eventually fail or slow to a crawl with the backlog. Using cable and components that have better signal to noise ratios, such as those rated to Cat 6, can help to prevent this potential problem.

As for the testing bandwidth, the official Cat 5e standard calls for testing across a bandwidth of 100 MHz. The Cat 6 standard calls for testing across a bandwidth of 250 MHz. The reality is that most computers and networking equipment only transmit across a frequency range of 100 MHz. (In the future, of course, actual utilization of greater bandwidth may become more common.)

When it comes down to it, however, this particular stat isn't all that important. Many cable companies tout the high bandwidth of their cable. Some even test up to as high as 700 MHz. It sounds great for marketing, but the truth is that the MHz rating is not the same as speed. All cable rated Cat 5e or Cat 6 is capable of Gigabit Ethernet. The MHz rating is just the frequency range used for testing the cable.

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