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Old 06-24-2009
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I used to own a wireless company in the Mid-West, we would use Butyl tape (specifically 3M 2228, it is usually referred to as mastic tape in the electricial and RF world, but it's same thing as far as I know) to weatherproof all of our connections up on top of cellular towers. The process we used to provide a 100% moisture and humidity proof all weather seal on sensitive antenna connectors and low voltage data connectors was as follows:

wrap a continuous strip of vinyal electricial tape slightly overlaping with each wrap around cable from 3/4" below the connector, up over the connector and to 3/4" past the connector on the other side of the cable.

wrap mastic tape (stretched to 1-3mm thick for most applications) around the entire connector, and past completly covering all electrical tape, with a 1/4" overlap onto the extending wire insulation on each end.

wrap starting from the bottom (assuming the cable & connector is running vertically) in a continuous strip, another layer of electrical tape starting 1/2" below the mastic tape and making sure to overlap aprox 3/16" to 1/4" over the layer below it all the way up to 1/2" above the top of the mastic tape.

two important notes to mention... 1) always try to wrap tape from the bottom up to create a overlap similar to how shingles or wood slats on siding overlap. this is just for extra protection and makes sure water drips down and over the tape and cannot collect or seep into it should it seperate for any reason 2) make sure the outer layer of tape has a large enough overlap on each wrap to withstand some expansion pressure as the mastic tape will expand some when it's hot, and it will ooze out the seams and stick to anything it touches if the tape doesn't contain it.

done properly you can make a connection that will stay completly air tight in 100mph wind and rain / sleet storms and easily last for 5-10 years without worry (or even if fully submerged for a few months, maybe longer). Plus if you didn't skip the bottom layer of tape, it will peel off and leave little to no residue on the connector when you need to disconnect it.
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