Cable bushings are plastic grommets inserted into a wall to provide a clean appearance for coax cable entry.
Cable bushings were originally designed for indoor use on sheet rock. Cable bushings are a low cost and fast alternative to installing traditional wall plates. At some point in the last few years some company, or individual, decided that bushings should also be used on exterior wall penetrations.
In My Opinion, that was a very poor idea. Bushings do provide a benefit when used on metal or even vinyl siding because they protect the cable from sharp edges. You still need to seal the hole with sealant, but the bushing does protect the cable. Bushings do not provide a benefit when used on wood siding. They in fact increase the chance that the cable will become pinched. Bushings do not accept paint very well, so when a home owner paints their home, the bushing is only thing left unpainted.
Cable bushings are often said to "seal wall openings", that is false. Cable Bushings do not seal wall openings unless you seal the bushing with sealant. Not only must you seal the bushing to the wall, you also need to seal the opening in the bushing that the coax runs through.
Without sealing BOTH sections you leave a path for cold air to flow into the wall opening. Today's homes are built to be air tight. Unsealed bushings break that barrier, unless sealed in both locations. Bushings actually lower protection by doubling the areas that need to be sealed. Silicone sealant will often separate from the plastic bushing, leaving the opening completely unsealed. Window and Door caulking seems to adhere better because the caulk is formulated to seal vinyl window and door frames. Caulking is also paintable, whereas 100% sealant sealant cannot be painted. Most installers only carry silicone and not caulking. With in a few months of installation, the silicone used to attach, and seal bushings can separate from the plastic leaving the hole unprotected.
For a quality satellite signal, coax cable cannot be pinched or kinked. The satellite industry has taken great steps to stop using metal staples, which can pinch cables, resulting in signal degradation. Coax cable is also not to have tight turns. Such turns can deform the inside of a coax cable tans still appear to look just fine. A 3 inch diameter bend is considered the minimum turn radius for a coax cable. The opening in a coax bushing requires that a coax cable enter the bushing strait on. A coax cable secured to the exterior of a wall must turn away from the wall, turn, and enter the bushing perpendicular to the wall. This leaves the cable exposed to damage.
The image on the left shows a cable entry that stays flush to the wall. Once sealed this opening is almost unnoticeable.
The bushing on the right requires the cable to turn away from the wall before entering the opening. The turn out is required to maintain the minimum bend radius.
Many times a coax cable feeds through a wall, and through another bushing. If the coax cable is pulled from the inside, the cable will be kinked against the exterior bushing
A cable that must turn away from an exterior wall is susceptible to damage. Any thing, or anyone that pushes against the cable will cause a pinch in the cable as the minimum bend radius is removed and the cable is forced into a 90 degree turn at the bushing. This is the best case to support NOT using bushings on a wood siding exterior wall.
Traditional installers will drill a hole at a downward angle. This allows for a smaller opening, and still provides an opening that keeps the cable flush with the wall. A hole drilled downward also reduces the chance that water will follow along a cable and enter the wall cavity. In the example to the right, the installer must drill the minimum size hole for the cable at an angle. Then the inside hole is drilled larger to accept the bushing or a wall plate.
A growing amount of installation companies have started requiring their installers to use bushings on all exterior wall penetrations. This move makes no sense. If your installer installs cable bushings on a wood siding exterior wall, it is because they have no choice, or they have been properly trained . Some installers may be fined for failing a QC check because they did not follow installation guidelines. You are not required to allow the installer to use bushings. It is your home and you have the final word. If your installer objects, then have them call a supervisor to note your account that this is your decision.
I hope someday soon, these companies will come stop this stupid practice.
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