The Lightning Protection System (LPS) is the equipment commonly known as a lightning rod, which is composed of three main parts: the air terminal (captor), conductor, and grounding, connected by connections and serve to protect people and buildings from lightning strikes. This article was originally written by Patrícia Lins.

I will start this post by posing a question aimed at discussing a dangerous assertion I heard a few weeks ago: “Does keeping the grounding meshes isolated ensure the safety of people, equipment, and installations?”

We know that grounding is an intentional physical connection of the protective conductor, metallic casings of equipment, conductive metallic elements such as metallic pipes not intended for carrying electrical current in the installation, with the aim of providing safety to people (against electric shock due to step and touch voltage) and equipment. We also know that the better the equipotential bonding between all these elements of the installation, the more effective the dissipation of the electric current from a lightning strike, preserving the installation and the physical integrity of people.

Moreover, although we should separate the main grounding mesh, called the power mesh (which has a high impact and is directly connected to the lightning down conductors of a building) from the Signal Reference Meshes for sensitive equipment, we must keep them connected through their respective BEP/TAP (Main Equipotential Bonding Bus / Main Grounding Terminal), connected by protective conductors.

Hence:

1. Considering that isolated meshes will ensure safety would be to disregard that the soil, no matter how high its electrical resistivity is, is also conductive, and even without physical connection between the meshes, it would provide coupling that could induce currents between them?
2. Wouldn’t equipotential bonding eliminate or minimize the possibility of step voltage between the meshes?
3. On the other hand, wouldn’t this connection imply the risk of the metallic casings of the equipment carrying a high potential at the moment of the discharge?

In short, should the grounding meshes of an installation be isolated or not?

First of all, keeping the meshes isolated is by itself a risk, as it represents intentionally disconnected interconnection points. In other words, with this action, equipotential lines are intentionally formed, and anyone who remains simultaneously between two equipotential lines, with different potentials, would be affected by electric shock due to step voltage.

Furthermore, even if there is no physical connection between the meshes, no matter how high the electrical resistivity of the soil is, some environmental conditions, such as high humidity in the air and lower temperatures, for example, contribute to varying the impedance of the soil, and it also begins to have better electrical conductivity characteristics. In other words, the electromagnetic effect caused by the passage of electric current in one mesh is propagated through the soil, by electromagnetic induction, inducing currents in other meshes, even if they are physically disconnected. At this point, the disconnection between the meshes worsens the effects of the formation of dangerous potential gradients in the soil, leading to equipment and installation failures (including electrical protection equipment), as well as a risk to human life. This is because the electromagnetic compatibility of equipment is compromised when the meshes are disconnected from each other.

In the case of a lightning strike, there is a current impulse of the order of tens of kA, for milliseconds. This current needs a low-impedance path to be dissipated, and this path is the grounding meshes. The more interconnection points, the more equipotentialized, that is, better distributed this current flow will be. This good distribution of the current flow is necessary to avoid dangerous overvoltages, which can either burn equipment or cause shocks to people (due to step voltage).