{"id":83249,"date":"2026-09-28T09:22:23","date_gmt":"2026-09-28T12:22:23","guid":{"rendered":"https:\/\/a3aengenharia.com\/?post_type=articles&p=83249"},"modified":"2026-09-28T09:22:23","modified_gmt":"2026-09-28T12:22:23","slug":"franklin-air-terminal-lps-lightning-rod-faraday-cage-air-termination","status":"publish","type":"articles","link":"https:\/\/a3aengenharia.com\/en-us\/content\/technical-articles\/franklin-air-terminal-lps-lightning-rod-faraday-cage-air-termination\/","title":{"rendered":"Franklin Air Terminal in LPS: Lightning Rods, Faraday Cage and Air-Termination System"},"content":{"rendered":"\n

The Franklin air terminal<\/strong> is one of the best-known elements of a lightning protection system. In common usage, it is often called a Franklin lightning rod<\/strong> or simply a lightning rod. In technical design, however, it should be understood as part of the LPS air-termination system<\/strong>, not as a standalone solution.<\/p>\n\n\n\n

In an LPS, air-termination is the subsystem responsible for intercepting lightning at technically defined points. This interception can be provided by Franklin-type air terminals, conductor meshes, natural components of the structure, structural solutions and geometric criteria defined in the design.<\/p>\n\n\n\n

For this reason, the choice between a Franklin air terminal, Faraday cage, structural LPS or another air-termination arrangement should consider the building geometry, protection class, positioning methods, down conductors, grounding, equipotential bonding and integration with internal systems.<\/p>\n\n\n\n

Franklin air terminal, lightning rod and LPS: how are these terms related?<\/h2>\n\n\n\n

The term lightning rod<\/strong> is widely used and usually refers to the visible component installed on the roof. The LPS<\/strong>, on the other hand, is the complete lightning protection system, comprising air-termination, down conductors, grounding, equipotential bonding, surge protection measures, technical documentation and inspection.<\/p>\n\n\n\n

The Franklin air terminal is one type of air terminal. It can be part of the external LPS, but it does not represent the entire system. A technically adequate design must define where the air terminal will be installed, which protection zone it provides, how the current will be conducted, which down conductors will be used and how the system will be interconnected with grounding and equipotential bonding.<\/p>\n\n\n\n

This distinction is important because many failures in existing installations occur when the lightning rod is treated merely as a metal rod installed at the highest point of the building, without risk assessment, detailed design, documentation or verification of interfaces with the electrical installation.<\/p>\n\n\n\n

What is a Franklin air terminal?<\/h2>\n\n\n\n

The Franklin air terminal<\/strong> is an air-termination terminal used to intercept lightning within a protection zone defined by the LPS design. It is generally associated with a metal rod installed at an elevated point, connected to down conductors and the grounding system.<\/p>\n\n\n\n

In practice, Franklin air terminal performance does not depend only on the rod. The effectiveness of the system depends on installation height, positioning, design method, quantity and arrangement of down conductors, continuity of connections, grounding, equipotential bonding and the protection class defined in the design.<\/p>\n\n\n\n

For this reason, expressions such as complete Franklin air terminal<\/strong>, Franklin air terminal with mast<\/strong>, Franklin air terminal with one down conductor<\/strong> or Franklin air terminal with two down conductors<\/strong> must be interpreted carefully. The number of down conductors and the system configuration should not be selected as a commercial package, but defined by technical design.<\/p>\n\n\n\n

Is a Franklin lightning rod mandatory?<\/h2>\n\n\n\n

There is no single answer for every building. The need for an LPS must be defined by technical assessment according to NBR 5419, considering risk, exposure, occupancy, building use, operational continuity, location, height, internal systems and the consequences of a lightning strike.<\/p>\n\n\n\n

When protection is required, the design may use a Franklin air terminal, an air-termination mesh, natural components, a structural LPS or a combination of solutions. Therefore, the correct question is not only whether a Franklin lightning rod is mandatory, but whether the building requires an LPS and which air-termination system is technically appropriate.<\/p>\n\n\n\n

For the decision on whether protection is required, also see When does a building need an LPS?<\/a>.<\/p>\n\n\n

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Need to assess whether the existing air-termination system is adequate for the building risk?<\/strong><\/p>\n\n\n\n

A3A Engenharia performs LPS inspections, document reviews and technical verification of air terminals, down conductors, grounding, equipotential bonding and surge protection. Request an LPS inspection<\/a>.<\/p>\n<\/div>\n\n\n\n\n

Air-termination system in an LPS<\/h2>\n\n\n\n

The air-termination system is the part of the external LPS intended to intercept lightning. It must be coordinated with the shape of the building, elevated points, edges, roofs, metal structures, equipment installed at the top of the building and elements that may alter exposure to lightning.<\/p>\n\n\n\n

In design, the air-termination system should not be analyzed in isolation. It must be coordinated with down conductors, grounding, equipotential bonding, SPDs, protection of internal systems and the technical documentation delivered with the project.<\/p>\n\n\n\n

NBR 5419-3<\/a> is the cluster content that examines the external LPS in greater depth, including air-termination, down conductors and grounding.<\/p>\n\n\n\n

Franklin air terminal or Faraday cage: which is better?<\/h2>\n\n\n\n

The choice between a Franklin air terminal<\/strong> and a Faraday cage in the LPS<\/strong> depends on the building. The Franklin air terminal tends to be associated with localized interception points. The Faraday cage, on the other hand, is a distributed air-termination solution, normally associated with conductor meshes installed on the roof and exposed parts of the structure.<\/p>\n\n\n\n

In buildings with simple geometries, well-defined elevated points and smaller areas, the Franklin air terminal may be technically viable. In buildings with extensive roofs, multiple volumes, parapets, outdoor equipment, technical areas and complex geometries, an air-termination mesh may be more suitable.<\/p>\n\n\n\n

The decision should not be based only on cost, aesthetics or installation preference. It should be based on risk assessment, protection class, positioning method and coordination with down conductors, grounding and internal systems.<\/p>\n\n\n

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Need to turn air-termination, down conductors and grounding into an executable design?<\/strong><\/p>\n\n\n\n

An LPS design defines the air-termination system, down conductors, grounding, equipotential bonding, technical documentation and inspection criteria according to NBR 5419. Learn about LPS Design<\/a>.<\/p>\n<\/div>\n\n\n\n\n

Faraday cage in the LPS<\/h2>\n\n\n\n

A Faraday cage in the LPS<\/strong> uses a network of conductors to create a distributed protection zone. This solution is common in buildings where a single rod or a small number of point air terminals does not adequately represent the exposed roof geometry.<\/p>\n\n\n\n

The air-termination mesh must be coordinated with down conductors, connections, metallic elements, grounding and equipotential bonding points. The objective is to conduct lightning current along technically defined paths, reducing the risk of dangerous sparking, continuity failures and structural damage.<\/p>\n\n\n\n

Structural LPS and natural air-termination<\/h2>\n\n\n\n

A structural LPS<\/strong> may use elements of the building itself as part of the protection system when this is technically permissible and properly documented. Metallic elements, reinforcement bars and natural components may play a role in the LPS, provided there is continuity, coordination and verification according to technical criteria.<\/p>\n\n\n\n

This type of solution requires care because it interfaces with structural design, electrical design, grounding, inspection and documentation. It should not be assumed merely because the building has visible metallic elements or embedded reinforcement.<\/p>\n\n\n\n

Rolling sphere method and protection zone<\/h2>\n\n\n\n

The rolling sphere method<\/strong> is one of the criteria used to verify LPS protection zones. It helps assess which parts of the building are exposed and where air terminals need to be positioned.<\/p>\n\n\n\n

For Franklin air terminals, the rolling sphere method is especially important to avoid a false perception of protection. Installing a rod at an elevated point is not enough; it is necessary to verify that the area to be protected is effectively within the protection zone compatible with the LPS class.<\/p>\n\n\n\n

For a deeper discussion of this criterion, see the specific article on the rolling sphere method in LPS<\/a>.<\/p>\n\n\n\n

Franklin air terminal and LPS down conductors<\/h2>\n\n\n\n

After interception, lightning current must be safely conducted to ground. For this reason, the Franklin air terminal must be analyzed together with the down conductors.<\/p>\n\n\n\n

The number, positioning and routing of down conductors influence current distribution, sparking risks, separation distances, fa\u00e7ade compatibility and integration with the grounding system.<\/p>\n\n\n\n

In existing installations, it is common to find air terminals installed without adequate down conductors, down conductors with weak connections, improvised routes, lack of electrical continuity or missing documentation. These cases require technical inspection before any conclusion about compliance.<\/p>\n\n\n\n

Franklin air terminal, grounding and equipotential bonding<\/h2>\n\n\n\n

Grounding is an essential part of the LPS. The current intercepted by the Franklin air terminal must be conducted and dissipated by a compatible grounding system integrated with the building’s equipotential bonding.<\/p>\n\n\n\n

Lack of adequate equipotential bonding can create hazardous potential differences among exposed conductive parts, structures, piping, busbars, shields, electrical systems and telecommunications infrastructure.<\/p>\n\n\n\n

To examine the interface between the external LPS and grounding in greater depth, see the article on LPS grounding<\/a>. When the need involves specification, upgrades or detailed documentation of the grounding subsystem, also see Grounding Design<\/a> and Grounding and Equipotential Bonding<\/a>.<\/p>\n\n\n\n

Franklin air terminal, SPDs and protection of internal systems<\/h2>\n\n\n\n

The Franklin air terminal and the external LPS reduce risks associated with a direct lightning strike to the structure, but they do not eliminate the need for surge protection in internal systems.<\/p>\n\n\n\n

Electrical installations, CCTV, access control, automation, telecommunications and data networks can be affected by conducted or induced surges. For this reason, the design should consider SPDs<\/a>, SPD coordination<\/a>, SPDs for data lines<\/a>, Surge Protective Devices<\/a> and the criteria of NBR 5419-4<\/a>.<\/p>\n\n\n

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Air-termination, grounding and SPDs must be coordinated.<\/strong><\/p>\n\n\n\n

In addition to the external LPS, electrical systems, CCTV, automation, telecommunications and IT require coordinated surge protection measures. See surge protection measures<\/a>.<\/p>\n<\/div>\n\n\n\n\n

Common mistakes in systems with Franklin air terminals<\/h2>\n\n\n\n

Among the most common mistakes are installing the rod without a risk assessment, positioning the air terminal without verifying the protection zone, using too few down conductors, leaving connections exposed to corrosion, ignoring separation distances, failing to integrate grounding, omitting SPDs, failing to document the system and not performing periodic inspections.<\/p>\n\n\n\n

It is also common to treat the air terminal as an isolated product. In engineering, the Franklin air terminal should be part of a complete LPS solution, with a technical design narrative, drawings, specifications, ART, inspection criteria and integration with the other building systems.<\/p>\n\n\n\n

When should an LPS design or inspection be commissioned?<\/h2>\n\n\n\n

Design or inspection is recommended when the building does not yet have an LPS, when there is uncertainty about whether protection is required, when air terminals are installed without documentation, when renovations or expansions occur, when equipment failures recur or when insurers, audits and regulatory authorities require technical evidence.<\/p>\n\n\n\n

A3A Engenharia provides LPS design<\/a>, LPS inspection and technical documentation<\/a>, LPS technical reports<\/a> and upgrades of existing systems.<\/p>\n\n\n\n

Integration of the Franklin air terminal with LPS design<\/h2>\n\n\n\n

The Franklin air terminal must be assessed within the complete lightning protection design. The definition of the air-termination system must be coordinated with NBR 5419<\/a>, the external LPS under NBR 5419-3<\/a>, air-terminal positioning, down conductors, grounding, equipotential bonding and the actual conditions of the building.<\/p>\n\n\n\n

In existing buildings, the technical assessment should also consider whether the protection zone was verified using the rolling sphere method<\/a>, whether the system is documented, whether electrical continuity exists at the connections and whether internal systems are protected against surges. For an overview of the subject, also see the article on lightning rods<\/a>.<\/p>\n\n\n\n

Technical references<\/summary>\n

[1] ABNT NBR 5419 \u2014 Lightning protection. Consult the current version from an official source or licensed standards collection.<\/p>\n\n\n\n

[2] ABNT NBR 5419-3 \u2014 Physical damage to structures and life hazard. Consult the current version from an official source or licensed standards collection.<\/p>\n\n\n\n

[3] ABNT NBR 5419-4 \u2014 Electrical and electronic systems within the structure. Consult the current version from an official source or licensed standards collection.<\/p>\n\n\n\n

[4] ABNT NBR 5410 \u2014 Low-voltage electrical installations. Consult the current version from an official source or licensed standards collection.<\/p>\n<\/details>\n\n\n\n

Frequently asked questions<\/summary>\n
What is a Franklin air terminal?<\/strong>

A Franklin air terminal is an air-termination terminal used in an LPS to intercept lightning within a protection zone defined by the design.<\/p><\/div>

Is a Franklin air terminal the same as a lightning rod?<\/strong>

In common usage, the Franklin air terminal is often called a lightning rod. Technically, it is only one component of the LPS, which also includes down conductors, grounding, equipotential bonding, SPDs, documentation and inspection.<\/p><\/div>

When should a Franklin air terminal be used in an LPS?<\/strong>

Use of a Franklin air terminal depends on building geometry, risk assessment, protection class, positioning method and coordination with down conductors, grounding and internal systems.<\/p><\/div>

What is a Faraday cage in an LPS?<\/strong>

A Faraday cage in an LPS is a distributed air-termination solution, normally formed by conductor meshes installed on the roof and exposed parts of the building.<\/p><\/div>

Does a Franklin air terminal eliminate the need for SPDs?<\/strong>

No. The Franklin air terminal intercepts lightning as part of the external LPS. Protection of internal electrical and electronic systems requires SPDs, equipotential bonding and coordinated surge protection.<\/p><\/div>

Does a Franklin air terminal require a technical design?<\/strong>

Yes. Positioning, protection zone, down conductors, grounding and system documentation must be defined by a legally qualified professional in an LPS design.<\/p><\/div><\/div>\n<\/details>\n\n\n\n

Additional technical materials<\/summary>\n