System information

has a clear, unobstructed path to the best ground you can afford to put in.
So what constitutes a good ground and a clear unobstructed path? Remember when dealing with
lightning, that we're talking about static DC discharge of extremely high voltages. Also understand that
while lightning is DC, it acts like high frequency AC (basically radio frequency – RF – signal). That
means that what we install has to conform to good radio signal passing procedures. If you aren't
convinced lightning acts like RF in a circuit, turn on an AM radio during a storm and you can hear
strikes miles away.
High frequency RF travels over, not through, a conductor. The more surface area you present, the
better. Flat braid or pipe strap works better than round conductors. Along those same lines, multi-
strand conductors work better than solid conductors (more surface area). Arc-welding cable, while
expensive, makes an excellent conductor.
The pathway for carrying lightning to ground should be as straight as possible. If you make one or
more 360 degree wraps in a cable (the smaller the diameter, the greater the effect), you will make a
choke or coil that will impede the flow of RF energy. In fact, one lightning dissipation device is made
with 10 turns of ½ inch square copper bar. One end is sharpened and functions as the lightning rod, the
other end is tied to ground. Lightning striking this rod takes a great deal of time (relatively speaking)
to pass through this coil and is reduced from thousands of volts to mere hundreds and runs to ground
safely. But use of a coil like this runs the risk of side flashing (lightning arcing through any insulator to
other parts of the tower structure or cables running parallel to the ground lead) until after it has passed
through the coil.
Whenever possible, put your systems 5 feet or more below the top of the tower. This is not always
possible, but systems/antennas at the top of the tower will be at greatest risk. Ensure you have good,
well-grounded lightning protectors just outside the radio enclosure (which should be made of metal, not
plastic). Never put a lighting protector inside a metal box. And use grounded POEs. The most
commonly available POEs are not grounded, but for outdoor cable runs, this is important. Your choice
of lightning protectors is important as well. Gas discharge tubes will react faster, although the
discharge tubes will need replacing more often.
Cables
Ethernet/POE cables
Ethernet cables used outdoors should be the gel-filled outdoor rated cable. Using indoor cable outdoors
will work – for a while. But this cable is subject to degradation from the sun's ultra-violet rays and will
need frequent replacing. Doing it right the first time will save doing it over later.
Many folks worry about Ethernet cable picking up EMP (electro-magnetic pulse) from a lightning
strike and damaging Ethernet ports on WRAP cards and switches. This is usually an unfounded worry.
Ethernet ports damage first because of all the electronic equipment, they have the lowest tolerance to
power surges. Most electronic equipment is rated at 1000v. Ethernet ports are rated at 100v. While the
standards have changed, it will take some time to get these newer chips deployed. Damaged Ethernet
ports are usually damaged because they became an alternate ground path and lacked grounded POEs to