Essential Guide: SPDA and PDA in Electrical Engineering – Understand the Differences and Applications

Atmospheric discharges, commonly known as lightning, are powerful natural phenomena capable of causing severe damage to buildings, electrical and electronic equipment, and even posing risks to human lives. To mitigate these dangers, electrical engineering has developed robust protection systems, notably SPDA (Lightning Protection System) and PDA (Early Streamer Emission Air Terminal - ESE). Although both aim to protect against lightning, their approaches and operating principles are distinct.

What are SPDA and PDA?

Before we delve into the differences, let's understand what each term means:

• SPDA (Lightning Protection System): This is a comprehensive set of measures and components designed to intercept a direct lightning strike, safely conduct the lightning current to the ground, and dissipate it. Its objective is to protect the structure from physical damage and fires, in addition to reducing the risk of electric shocks. In Brazil, SPDA is extensively covered by the technical standard NBR 5419.

  
  

• PDA (Early Streamer Emission Air Terminal - ESE): Also known as an ionization air terminal or "radioactive lightning rod" (an old and imprecise term, as current models do not use radioactive material), the PDA is a specific type of air terminal that, theoretically, would have the ability to attract lightning to itself in an "anticipated" or "active" manner, even before the lightning leader reaches the ground or another part of the building. The PDA aims to create a preferred point of attraction for lightning.

  
  

Operating Principles

Conventional SPDA (Common):

The conventional SPDA, in its most common configurations (such as Franklin rods and Faraday Cages), operates based on the principle of interception, conduction, and dissipation.

1. Interception: A set of air terminals (rods, wires, meshes) is installed on the highest part of the building to directly intercept the atmospheric discharge.

   
   

2. Conduction: The lightning current is safely conducted by down conductors (copper or aluminum cables) to the earthing (grounding) system. These conductors are sized to withstand the high lightning current without overheating or being damaged.

   
   

3. Dissipation: The lightning energy is dissipated into the ground through a low-impedance earthing (grounding) system, composed of electrodes (rods, meshes) buried in the soil. Efficient grounding is crucial for system safety.

   
   

In addition to these main components, a complete SPDA also includes:

• Equipotential Bonding: Connecting the metallic parts of the building to the earthing (grounding) system to prevent dangerous potential differences.

  
  

• SPD (Surge Protective Devices): Components installed in electrical panels to protect electronic equipment from voltage surges induced by lightning or indirect discharges.

  
  

PDA (Early Streamer Emission Air Terminal - ESE):

The operating principle of the PDA is based on the anticipation of the upward leader. The theory behind the PDA is that by accumulating charge at its tip, it creates an intensified electric field that would "launch" an upward tracer before the natural electric field reaches the critical point for the formation of an upward tracer from a conventional lightning rod. In this way, the PDA would "attract" the lightning to itself within a larger protection radius than a conventional lightning rod.

Crucial Differences Between SPDA and PDA

Characteristic	Conventional SPDA (Franklin, Faraday Cage)	PDA (Early Streamer Emission Air Terminal - ESE)
Principle of Action	Intercepts lightning that strikes the structure, conducting it to the ground. Passive protection.	Aims to "anticipate" lightning attraction by generating an upward streamer. "Active" protection.
Standardization	Widely standardized by ABNT NBR 5419 (Brazil) and international standards (e.g., IEC 62305 series). It is the most accepted and used solution globally, with well-defined calculation and installation methods.	Its effectiveness and extended protection radius are controversial and not widely recognized by the most recent Brazilian and international technical standards (such as NBR 5419:2015 and IEC standards). NBR 5419:2015, in particular, removed any mention of this type of air terminal.
Scope	Protects the entire building, based on an integrated system of air terminals, conductors, and grounding, sized according to the required protection level.	The PDA is only one type of air terminal. Even if it were effective, it would still require a complete down conductor and grounding system to function, just like a conventional SPDA.
Reliability	High, based on decades of research and practical application, following rigorous normative standards.	Questionable in terms of proven effectiveness and actual protection capability. There are significant debates in the technical community regarding its validity and superiority over conventional systems.
Maintenance/Tests	Requires periodic inspections and maintenance, including earthing (grounding) resistance measurements.	Maintenance and testing can be more complex due to the "active" nature of the device, and proving its functionality in the field can be more difficult.

Components of an SPDA System (Overview)

A complete SPDA system, according to NBR 5419 (and aligned with international standards like IEC 62305), is composed of:

1. Air Termination System (Air Terminal): Responsible for intercepting the atmospheric discharge. This can be achieved by:

   
   

   • Rods: Metallic points elevated above the structure (e.g., Franklin rods).

     
     

   • Catenary Wires (Overhead Cables): Conductors forming a "cage" over the structure (e.g., Faraday Cage).

     
     

   • Natural Components: Metallic parts of the structure itself that can be used as air terminals.

     
     

2. Down-Conductor System: Conducts the lightning current from the air termination system to the earthing (grounding) system. It consists of conductive cables sized to handle high currents.

   
   

3. Earthing (Grounding) System: Disperses the lightning current into the ground. It consists of buried electrodes (rods, meshes, rings) with low earthing (grounding) resistance.

   
   

4. Equipotential Bonding System: Connects all metallic parts of the building (pipes, metal structures, etc.) to the earthing (grounding) system to prevent dangerous potential differences.

   
   

5. SPD (Surge Protective Devices): Components installed at the electrical service entrance and within internal panels to protect electronic equipment from voltage surges caused by direct or indirect strikes.

   
   

Given the technical and normative evidence, it is fundamental that electrical engineers and designers prioritize the use of Lightning Protection Systems (SPDA) based on recognized and standardized principles, such as the Franklin rod and Faraday cage methods, in accordance with ABNT NBR 5419 and international standards.

The safety of buildings and the protection of lives and property should always be the priority. Relying on systems whose effectiveness is widely questioned and not supported by current technical standards can lead to unnecessary risks. The correct specification, design, and installation of an SPDA ensure effective protection against the devastating effects of atmospheric discharges.

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