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E.g., a tree with a diameter of 30 cm or more can be split, exploded, broken or set on fire by a branch of the
main channel of the lightning, while a standard metal lightning rod, taking the main strike of the lightning,
survives, although it is much thinner than the tree.
4)
The enormous electrical pulses induce high currents and create high mechanical forces in both
the stricken and nearby objects. To prevent mechanical damage, the masts, antennas, antenna
feeders and the entire equipment of the respective grounding system should be mechanically
strong, reinforced and corrosion-proof, in accordance with the expected local effects on the
surface and underground.
5)
The grounding system should be built in such a way that the lightning current does not flow
through the protected object, or if it does, it should at least be considerably reduced by
redirecting its main part along the paths provided in the design. For that purpose, the
grounding system should be carefully planned and designed by thoroughly evaluating the
possible paths the lightning currents could go along. Some essential paths for such currents
are antennas, antenna feeders and the mains, because they are widely spread and have low
impedance to the ground.
6)
Currents passing through the protected object can be additionally reduced by creating
obstacles along the paths through the object, and redirecting the currents along the planned
protection paths. This can be done by threading ferrite tubes (toroids) along "unfavorable"
paths (i.e. the cables going to and from the protected object). This way, the predominant part
of the currents will be tapped to the planned protection path, i.e., through the main grounding
plate and all wires and cables connected to it and external to the building. The latter are
intentionally left without ferrite tubes - e.g., the system of grounding electrodes, the securing
ring of the building, the connections and the cables of the mains coming from outside.
Apart from lightning protection improvement, threading of ferrite tubes (toroids) on the power and signal
cables of the equipment in the radio station improves the electromagnetic compatibility (EMC) both between
the devices inside the radio station and between them and the outside devices.
7)
All objects in the area of antennas and nearby devices (within 6 m radius) – tuners, rotators
and alike - should be connected by low-impedance connections to a common point called main
grounding plate for the antennas and antenna devices, which in turn should be grounded using
low-impedance connection to the closest main grounding conductor of an existing or purpose-
built (individual) low-impedance grounding system for lightning protection in accordance with
all requirements of the local standards and regulations for electric safety, fire safety and
lightning protection.
Where antenna counterpoises exist, their connections to the main grounding plate and the connections of
the antenna devices should be positioned under the level of the counterpoises or buried underground, if the
antennas are designed this way.
To avoid damage or destruction by lightning, the antenna isolators, and the isolators sectioning the antenna
and mast bracings into smaller lengths, should be bypassed by pulse overvoltage limiters (lightning surge
arrestors). The limiter closest to the ground should be grounded to the main grounding plate, and if the
distance is too great, to an individual low-impedance grounding system for lightning protection.
Page 66 of 70 | S e c t i o n APPENDIX 1 | Lightning Protection
User's Manual | ACOM 06AT | Automatic Antenna Tuner and Switch
October 2022
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