Coax cables are intended to be pathways for low voltage and low wattage RF energy to and from your antenna. However, it is an adequate
pathway for destructive and deadly lightning strokes to enter into your home or laboratory. Proper planning is required to minimize
The better your coax is shielded, the lower its losses and the higher its voltage breakdown rating is, the more effectively it will operate as a lightning conduit into your lab or radio shelter. NO methodology nor devices can guarantee complete protection but the goal of lightning protection is to reduce the strike energy to a level that no longer presents a clear and present danger to personnel or equipment.
Threats to you and your radio equipment: It all begins outside. Note…It is NEVER safe to operate your radio in a storm.
Example Threats in addition to direct and near lightning strikes:
Precipitation voltages: (Usually a result of static build-up on the antenna from wind blown dust. This can be over 10,000 volts)
AC power transmission: (downed power lines)
Induced electrical currents: (nearby power lines)
Inductive RF coupling: (nearby transmitting antennas)
Capacitive coupling: (nearby transmitting antennas)
EMP & NEMP (Nuclear Electro Magnetic Pulses) A kind of Induced current with specific characteristics at very high levels.
What is an Arrestor?
Simply put, an Arrestor is an inline coaxial device that is designed to shunt dangerous currents and voltages to ground, BEFORE they can enter your building. Because lightning strokes are high voltage, high current and have fast rise times, they are very unpredictable and can exhibit some characteristics similar to high frequency phenomena.
Types of Arrestors:
There are 3 general types of Arresting methodologies for coaxial cable devices. Spark gap, direct short and filters. There are many variations but note that the two most critical considerations is their pass-band frequency and their clamping voltage. Absolutely NO single Arrestors are appropriate for all applications! Just as your antenna must match your system, so must the Arrestor. Failing on this point could result in serious damage or injury at some point. Direct short Arrestors are always your safest device but are not appropriate for active antennas and they are very narrow band devices.
Voltage and power ratings:
If Arrestors passed continuous current as electrical components do, their design would be child's play, but they in fact pass impulse currents instead. Very high currents at absurd voltages with fast voltage rise times and a relatively short duration. Numerous electrical phenomena can occur during their “ON” state as well. Tremendous magnetic forces, corona discharge, ionization, oxidation and metal deposition just to name a few. The ratings can vary considerably between models and those details exceed the level of information sharing in this format. NFPA 780, UL96 & 96A regulates such products installations.
Continuous protection or failure:
Most Arrestors are designed to take multiple lightning strokes before failure, however their design and quality are just some of the considerations as to whether an Arrestor will fail or will provide continuous protection after a strike event. Part of Saturn Antennas work load has been a result of customers failing to do regular site inspections and maintenance as well as failing to do post storm inspections. A direct lighting strike is not always required to damage antennas or supporting components. Arrestors and the coax weather seals should be checked after each lighting storm and repaired/replaced after a strike. They may only need a cleaning, replacement of gas tubes or complete replacement but continuing to use your system without inspections is akin to playing Russian roulette with Mother Nature.
© Copyright 2010-14 Saturn Antennas, LLC All Rights Reserved