The grounding system is established with the main objective of limiting the voltage with respect to ground, which can occur at a given moment in the metal frames, and prevent dangerous potential differences over allowing ground fault currents or discharge or atmospheric origin.
The grounding system of a lightning protection system is one of the most important parts of the system, as this the lightning currents and all its energy charge is dissipated.
The recommendations set by regulations such as IEC 623 053, NF C 17-102: 2011 and UNE 21186: 2011, indicate that grounding must have a low ohmic value (less than 10 Ω when the measurement is made at isolated low frequency any conductor element).
Depending on the protection system, they have indications marked by IEC 62305-3: 2011 for Franklin rods or Faraday cage or by UNE 21186: 2011 and NF C 17-102: 2011 for the PDC lightning rod.
Grounding for PDC Lightning Rods:
The dimensions of the ground will depend on the resistivity ρ= (Ω*m) of the terrain.
Grounding must be done for each down conductor and there are 2 types:
TYPE A GROUNDING TYPE: can be type A1 or A2
- TYPE A1:It consists of a crow’s foot configuration
- TIPO A2: Formed by the union of many inline or triangle vertical stakes and separated by a distance of at least equal to its length
GROUND TYPE B: ring electrode, this arrangement is a conductive ring in contact with the ground 80% of its length. It may be external to the electrode structure or foundation. Each down conductor, besides being connected to the ring, is to be further connected to a horizontal electrode at either at least a 4 m vertical electrode or to a minimum length of 2 m
Grounding for Franklin rod systems or Farady cage:
According to layout, 2 grounding systems exist:
TYPE A: formed by horizontal or vertical electrodes installed outdoors and connected to each down conductor. In type, the number of electrodes should not be less than 2, and should be distributed evenly.
Minimum length of each earth electrode must be:
- L1 for horizontal electrodes.
- 0,5 L1 for vertical or inclined electrodes.
L1 being the minimum length of horizontal electrodes shown in scheme.
In case we can not achieve these requirements, we will use the type B configuration.
TYPE B: It is formed by an outer conductor ring to the structure to be protected, in contact with the ground at least 80% of its length, installed at 0.5 m deep and 1 m separation from the structure.
It is recommended that the electrode number not be less than the number of down conductors with a minimum of two. A ring that would connect additional electrodes at points where the down-conductors are connected.
This Type B arrangement is recommended for rocky terrain, and is preferable to use with electronic systems or structures with a high danger of fire.