Lightning And Surge Protection For Cable Networks And Antennas For TV (Part 2)

Continued from part one:
Lightning And Surge Protection For Cable Networks And Antennas For TV (Part 1)

Protective Mechanisms

If an antenna is protected by isolated air-termination systems it means:

– That in the area of flat roofs an air-termination rod will be installed with the required separation distance s, putting the whole antenna arrangement (mast and antennas) in the protective zone of the protective angle (Figure 4).

Now the antenna arrangement is no longer in lightning protection zone LPZ 0_A (risk of direct lightning currents) but lightning protection zone LPZ 0_B (risk of indirect impulse currents and of the unattenuated electromagnetic field of lightning).

– That in the area of pitched roofs an air-termination rod will be installed with the required separation distance s using highly insulating distance holders (DEHNiso distance holders) to fix it at the antenna mast, putting the whole antenna arrangement (mast and antenna) into the protective zone of the protective angle (according to the applicable class of LPS) – Figure 5.

Also here the antenna arrangement is no longer in lightning protection zone LPZ 0_A (risk of direct lightning currents), but in lightning protection zone LPZ 0_B (risk of indirect impulse currents and of the unattenuated electromagnetic field of lightning).

These surge protective devices to be used both as single devices and for rail mounting protect the downstream devices against inductive and/or capacitive inputs of waveform 8/20 μs, arising from cloud/cloud flashes, distant strikes or direct strikes into the isolated air-termination system.

Surge protective devices Type 3 have to be provided for any electrical equipment with 230/50 Hz downstream the equipotential bonding bar, which is installed for the coaxial cable shields. Care has to be taken that the lightning equipotential bonding is carried out for all systems leading into the building.

A lightning protection system not being installed, the following is recommended:

– An air-termination rod mounted with insulated distance holders prevents from a direct strike to the antenna. For this the air-termination rod has to be connected with the earth electrode by a separately installed earthing conductor (Figure 7) to be guided preferably on the outside of the building and to be connected with the earth electrode at ground level.

– If the antenna mast is earthed directly, combined lightning current and surge arresters have to be provided (Figure 8), because partial lightning currents, which the surge arresters are not able to control, will be conducted in this case through the coaxial cables.

The antenna mast has to be connected with the earth electrode by an earthing conductor.

Underground utility lines of systems require combined lightning current and surge arresters being able to carry lightning currents. They also have to be mounted near the point of entrance into the building (Figure 9).

Reference: Lightning Protection Guide – DEHN Inc. (dehn.de)