The SPDA structure according to NBR 5419 is the starting point for any technical design intended to provide effective lightning protection. The standard clearly separates the external system, responsible for intercepting and conducting current to ground, from the internal system, which protects people and equipment against indirect effects, surges, and induced voltages. […]
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The SPDA structure according to NBR 5419 is the starting point for any technical design intended to provide effective lightning protection. The standard establishes a clear division between the external system — responsible for intercepting and conducting current to ground — and the internal system, which protects people and equipment against indirect effects, surges, and induced voltages. Understanding this integrated structure is essential to design, install, and maintain a technically reliable and standards-compliant SPDA.
In the previous article, we briefly introduced NBR 5419 -1 and its relevance to lightning-protection design. Now, as promised, we will explain how the SPDA is structured: its components, how they integrate, and how they act to ensure safety, standards compliance, and technical performance.
NBR 5419 divides the SPDA into external and internal systems, each with specific functions — but effective only when considered as a single, well-designed system.
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Preventive Measures (Protection Systems)
According to NBR 5419-1:2015 (Clause 8), the SPDA consists of two main subsystems:
External SPDA
Responsible for intercepting the lightning discharge and safely conducting it to the grounding system.
It is divided into:
- Air-termination system (rod, conductor, mesh, mast): intercepts the discharge and prevents it from striking the structure.
- Down conductors: conduct the current to ground in a controlled manner.
- Grounding system: dissipates the energy into the ground.
Internal SPDA (MPS — Surge Protection Measures)
Intended for protecting people and equipment against indirect effects, overvoltages, and induced currents.
Includes:
- Main and supplementary equipotential bonding
- Surge protective devices (SPDs)
- Electromagnetic shielding, routing, and cable separation
- Use of isolating interfaces.
Interaction Between the External and Internal Systems
The two systems cannot be treated in isolationNBR 5419 reinforces that protection effectiveness depends on the functional interaction among the parts, meeting the following requirements:
- A single, continuous grounding system shared by both;
- Compatibility between air-termination and shielding;
- SPDs correctly connected to the equipotential-bonding system;
- Electrical continuity of metallic structures;
- Proper treatment of incoming and outgoing interfaces (lines and power);
Normative Requirements and Design Implications
A standards-compliant SPDA should:
Have complete documentation: design reports, site plans, diagrams, and maintenance plan;
Be designed based on the risk assessment required by the standard;
Use components tested according to the parameters of Part 1 and Annex D;
Comply with the separation distance between active conductors and internal installations;
When We Talk About “Installing an SPDA,” We Mean Specialized Engineering
Designing an SPDA requires more than installing conductors and rods. It involves:
- Electrical calculation of lightning current;
- Assessment of energy distribution in the ground;
- Definition of the down-conductor topology (symmetrical, ring, radial);
- Integration with sensitive electrical and electronic systems;
Each decision affects people safety, equipment protection, and the technical compliance of the design.
Final Considerations
The structure of an SPDA, as defined by NBR 5419, is not limited to installing rods or conductors. It requires a systems approach in which external and internal components operate in an integrated manner to mitigate the direct and indirect effects of lightning discharges.
In practice, a well-designed SPDA results from correct application of the standard, risk assessment, and technical understanding of the interactions among air-termination, conduction, grounding, equipotential bonding, and protection of electronic systems.
Engage a Specialist.
A A3A Engenharia has a consolidated technical track record demonstrated by successful high-complexity projects, working in industrial, corporate, institutional environments and projects with strict normative requirements.
We specialize in the design, implementation, and regularization of Lightning Protection Systems, with comprehensive knowledge of NBR 5419:2015 and integration with other related technical standards.
Our services include:
- SPDA designs, with risk assessment and standards-based sizing;
- Installation of external and internal protection systems, with technical responsibility;
- Specialized consulting for upgrading existing structures;
- Issuance of technical reports, inspections, and surveys for normative and contractual compliance;
- Complete documentation with CREA, including ART records, design reports, and technical reports;
Do Not Miss the Next Article in the NBR 5419: Risk Assessment
Determining whether a lightning-protection system is required is not subjective — it must be technically justified.
A risk assessment, as established in NBR 5419-1 and detailed in Part 2 of the standard, is the starting point for any SPDA design, serving as the basis for selecting the protection level, sizing components, and providing technical justification to regulatory authorities.
In the next article, you will understand how this assessment is performed, which variables affect the result, and why it is essential to ensure compliance, technical rationality, and effective safety.
Do not miss the next content in the series and deepen your understanding of the normative criteria governing lightning-protection systems.
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Talk to a specialist engineer and ensure safety, compliance, and technical efficiency for your structure.
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Articles that complement this topic:
“If you have not yet read the article Introduction to NBR 5419, we recommend starting there to understand the normative context before going deeper into SPDA structure.”
Also read:
Lightning Discharges — Origin and Impact
Effects of Lightning Discharges
Follow our profiles for access to technical content on designs, standards, and field-applied solutions.
Technical References
[1] BRAZILIAN ASSOCIATION OF TECHNICAL STANDARDS. ABNT NBR 5419 — Lightning protection. Consult the current series in the ABNT Catalog.
[2] INTERNATIONAL ELECTROTECHNICAL COMMISSION. IEC 62305 — Protection against lightning. Consult the official series in the IEC Webstore.
[3] FEDERAL COUNCIL OF ENGINEERING AND AGRONOMY. Technical Responsibility Annotation — ART. See guidance from Confea.
Frequently Asked Questions
The external SPDA essentially consists of air-termination, down-conductor, and grounding subsystems, integrated with internal equipotential-bonding and surge-protection measures according to the design.
Not exactly. Lightning rod is a common expression associated with air-termination. SPDA is the complete system, involving risk assessment, air-termination, down conductors, grounding, equipotential bonding, SPDs, and documentation.
No. Grounding is one of the SPDA subsystems and must operate together with air-termination, down conductors, equipotential bonding, and protection measures for internal systems.
Renovations, expansions, changes of use, roof modifications, new external equipment, damage, missing documentation, or relevant changes in risk justify a technical review.
