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Where & When to use LMR400 and WILSON-400 Plenum Cables?

May 19, 2020

When and where to use Wilson LMR-400 plenum and Wilson-400 plenum cables in cell phone signal booster system installations? Watch video below about Plenum cables or read this blog below the video.

What is a plenum cable?

Wilson Pro has two different types of plenum cables: LMR400 plenum cable and Wilson 400 plenum cable. Both cables come in 500 ft. spools and can be used in installations with Wilson Pro boosters as well as other brands. One of the first things you probably want to know is what is a plenum cable? A plenum cable is a special cable that has a fire resistant jacket. What this jacket does, is that it only burns at a higher temperature.

This prevents a fire from spreading through a building as quickly, and it lets the communication data transfer through the cables when needed the most. It also lets off less toxic smoke when it does get lighted by fire. These're good features to have in coaxial cables because if the building does catch on fire, then such factors will prevent fire from spreading as quickly, and it is also not going to pump the toxic smoke through air ducts and through its air system all across the building.

When is plenum cable required?

It is really important to use Plenum cables in Plenum spaces where it is required. To do this, you need to know what are plenum areas where it is required. When you're putting the cable in a plenum space, the easiest way to figure out if the space is a plenum space is to walk around and find an air intake vent up in the drop ceiling. Once you have located one of those, you can hop on a chair or step ladder and pop open the ceiling tile and look up into the ceiling. If you see a duct going back to the air hauler, then it is not a plenum space, that is a closed air system. Plenum cable will not be required in such a space.

However, if there's no duct going back to the air hauler, then it is an open air system which is a plenum space. That will require plenum cable. Plenum cables must pass rigorous testing by a nationally-recognized test lab. Probably, one of the most common ones that most people heard of is UL. However, there're several other places that will verify the cable. What they do is they will do a bunch of testing, lighting it on fire and putting it through a lot of different circumstances to see if it is going to produce toxic smoke and also not light on fire quickly.

By using plenum cable, you're going to be ensuring that you're not spreading toxic fumes around the building and also making sure that your system is to code for that building.

Performance of plenum cable.

Now we're going to get to the most important part of the two different types of cables, which is the performance. It relates to mainly attenuation of the cable, which is the loss that occurs when the signal crosses or travels through the length of the cable. As a reference, the lower attenuation the better. We have the two different types of cable LMR400 and Wilson400. LMR-400 has a little bit lower attenuation, so it is a little higher performance cable and the Wilson 400 cable is available at a better price point.

Therefore, depending on the type of job you're doing, you may use either type of cable. Using the LMR 400 cable, you're going to have 5.7 decibels of attenuation over a hundred feet at 1800 MHz. If you're using the Wilson 400 cable, you're going to have 7.2 decibels of attenuation over each 100 feet section of cable. That essentially means is the difference between the LMR 400 and the Wilson 400 is about 6 decibels, which is significant. It is something you want to consider when deciding what type of cable to use.

If you're doing a system like a Wilson Pro 70 with one donor antenna, and only one server antenna, you may only be looking at two to three decibels of difference of attenuation between the two different types of cables. This can be a lot more manageable, depending on the outside signal strength and the different factors contributing to the insulation. If outside signal strength is average, you may get by just fine without using Plenum cables.

What cable works best?

To decide which cable works best, you just need to understand what you're giving up in the form of the signal loss in the cable. It is important to understand how much attenuation you can handle on the system you're picking and the cable that works best for the job that you're doing. As an example about the difference between the two different types of cable, let us assume you would be installing a Wilson 4000 booster system. In this system, you would be using 3 server antennas and a donor antenna with a 100-feet cable run in between the booster in each antenna.

Using the Wilson 400 cable, you would have 7.2 decibels of attenuation for each run at 1800 MHz. Using the LMR 400 cable, you have 5.7 decibels of attenuation for each 100 ft. run. What this means is with the LMR-400 cable, you would have six decibels less loss of attenuation using that cable over the Wilson-400. That 6 decibels is significant. That is 6dB lower Gain power that you could be using in different parts of the system to boost your cell phone signal. If exterior signal is strong, you will have no problem losing 6 dB in signal loss. But if exterior signal is very weak, that 6dB loss becomes too critical to lose. 

This is how you can figure out when you can use each different type of cable. If it is an installation where you're putting in a pro 70 system, and you just have one run of cable to the donor and one to the server, you're only going to have two or three decibels attenuation using the Wilson 400 plenum than over the LMR 400 plenum. In that situation, that attenuation is acceptable.

Tools for terminating the cable.

We carry plenum cables and tools so you can terminate the cable. This is important because you don't always know the length of cable that you're going to need on the job site until you get to the job site. With these tools, you can make custom lengths of cable on the site. We have a cable prep tool and what this does is, it strips the jacket back just a perfect amount and also the dielectric and it debursts the conductor, so you can get a really good solid and secure connection. We also have a crimp-on connector that can be used in the field to terminate on site. Also a crimp tool, which crimps the connector on the cable. With such tools, you can make custom lengths of cable on the site that will work perfect for your system.

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  • I thought I was well-versed in cell phone boosters and their accessories but somehow I never knew about plenum cables. They sound like they’re great to have given their fire resistance and tendency to give off less toxic smoke. I would not be shocked to see them become mandatory soon as people learn about their safety features.

    Isabella Fischer on
  • I dig how your site provides information from everyone ranging from the novice (like me) to the expert (people who would have to know where and when to use these plenum cables. I imagine you get a lot of different readers here.

    J. Silvas on

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