{"id":83290,"date":"2026-09-28T09:50:17","date_gmt":"2026-09-28T12:50:17","guid":{"rendered":"https:\/\/a3aengenharia.com\/?post_type=articles&#038;p=83290"},"modified":"2026-09-28T09:50:17","modified_gmt":"2026-09-28T12:50:17","slug":"thermomagnetic-circuit-breaker-how-it-works-when-to-use","status":"publish","type":"articles","link":"https:\/\/a3aengenharia.com\/en-us\/content\/technical-articles\/thermomagnetic-circuit-breaker-how-it-works-when-to-use\/","title":{"rendered":"Thermomagnetic Circuit Breaker: What It Is, How It Works and When to Use It"},"content":{"rendered":"\n<p class=\"wp-block-paragraph\">A thermomagnetic circuit breaker is a protection and switching device that combines two operating mechanisms: a thermal mechanism associated with overload protection and a magnetic mechanism associated with rapid operation at high currents such as short circuits.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The direct answer is: <strong>a thermomagnetic circuit breaker protects electrical circuits against overcurrents by automatically interrupting the supply when current exceeds the limits established for the circuit<\/strong>. It should not be selected only by amperage. Correct specification depends on design current, conductor capacity, trip curve, breaking capacity, prospective short-circuit current and coordination with other protective devices.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">In low-voltage electrical installations, thermomagnetic circuit breakers are used in distribution boards, final circuits, feeders, electrical panels, lighting circuits, socket-outlets, dedicated equipment and commercial or industrial applications. Although common, incorrect selection can cause nuisance trips, conductor overheating, protection failure or incompatibility with the actual installation.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">What is a thermomagnetic circuit breaker?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">A thermomagnetic circuit breaker combines two forms of overcurrent protection. The first is thermal protection, intended for overloads. The second is magnetic protection, intended for high currents of short duration, mainly short circuits.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The term \u201cthermomagnetic\u201d comes from this combination. \u201cThermal\u201d relates to heating caused by electric current. \u201cMagnetic\u201d relates to the magnetic field generated when a high current flows through the device.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">In practice, the circuit breaker carries current under normal conditions and opens the circuit when an abnormal condition occurs. This opening may happen after a certain time in the case of overloads, or very quickly in the case of very high currents.<\/p>\n\n\n\n\n<h2 class=\"wp-block-heading\">What is a thermomagnetic circuit breaker used for?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">A thermomagnetic circuit breaker protects the circuit against overcurrents. An overcurrent is any current above that intended for safe circuit operation. It can result from overload or short circuit.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">During an overload, current remains above the permissible value for a certain period. This can cause heating in conductors, connections, terminals, busbars and electrical-panel components.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">During a short circuit, current rises rapidly and can reach values far above normal circuit current. In this case, interruption must be fast and safe, compatible with the device breaking capacity and with the prospective short-circuit current at the installation point.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Therefore, a thermomagnetic circuit breaker is not intended only to protect the connected equipment. Its primary function under NBR 5410 is to protect the installation and conductors against the thermal and mechanical effects of overcurrents.<\/p>\n\n\n\n\n<h2 class=\"wp-block-heading\">Difference between thermal, magnetic and thermomagnetic circuit breakers<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">The terms \u201cthermal,\u201d \u201cmagnetic\u201d and \u201cthermomagnetic\u201d distinguish the device operating mechanism.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A thermal device operates according to heating caused by current over time. It is suitable for overload protection because an overload is normally a current above normal that persists for a period.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A magnetic device operates through an electromagnetic effect and responds quickly to high currents. This type of operation is associated with short circuits and intense current peaks.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A thermomagnetic circuit breaker combines both functions. It has a thermal operating region and a magnetic operating region. Therefore, it can protect against overloads and short circuits when correctly selected, installed and coordinated with the rest of the installation.<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table><tbody><tr><td>Mechanism<\/td><td>Mainly operates on<\/td><td>Main characteristic<\/td><\/tr><tr><td>Thermal<\/td><td>Overload<\/td><td>time-delayed operation due to heating<\/td><\/tr><tr><td>Magnetic<\/td><td>Short circuit and high currents<\/td><td>rapid operation due to magnetic field<\/td><\/tr><tr><td>Thermomagnetic<\/td><td>Overload and short circuit<\/td><td>combines both operating mechanisms in the same device<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<div class=\"wp-block-a3a-destaque\">\n\n<p class=\"wp-block-paragraph\"><strong>Thermal and magnetic operation explain trip-curve selection<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">After understanding the thermomagnetic mechanism, the next step is to analyze how the curve influences magnetic operation. Also see <a href=\"\/conteudo\/artigos-tecnicos\/curvas-disjuntores-curva-b-c-d\/\">Circuit-Breaker Trip Curves: Type B, Type C and Type D explained<\/a>.<\/p>\n\n<\/div>\n\n\n\n\n<h2 class=\"wp-block-heading\">How does thermal operation work?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">The thermal operation of a circuit breaker responds to heating produced by current flow. When current remains above the permissible value for a certain time, the thermal element deforms or moves enough to trigger the opening mechanism.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">In many circuit breakers, this function is associated with a bimetallic strip. The principle is simple: different materials expand differently when heated. As temperature rises because of current, the strip bends and can trigger the breaker.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">This operation is not instantaneous. It follows an inverse-time characteristic: the higher the overload current, the shorter the operating time tends to be. A small overload may take longer to open the circuit, while a high overload tends to cause faster operation.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">This characteristic is important because many circuits may experience small transient variations without representing a fault. The breaker should not operate for every fluctuation; it should operate when current magnitude and exposure time become a risk to conductors and components.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">How does magnetic operation work?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Magnetic operation responds to very high currents. When a high-intensity current passes through the circuit breaker, the resulting magnetic field can rapidly trigger the circuit-opening mechanism.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">This operation is used mainly for short circuits. Unlike overload, which may evolve through gradual heating, a short circuit requires a rapid response because it involves high currents, electrodynamic stresses and significant energy in a short period.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">It is in magnetic operation that circuit-breaker trip curves become especially relevant. B, C and D curves indicate different current ranges for magnetic tripping. Type B is more sensitive to short-duration high currents. Type C tolerates larger peaks. Type D tolerates still higher peaks before magnetic operation.<\/p>\n\n\n\n\n<h2 class=\"wp-block-heading\">Overload and short circuit: what is the difference?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">An overload occurs when circuit current remains above the intended value without necessarily involving direct contact between conductors or a solid fault. It can result from too many connected devices, load expansion without circuit review, a motor operating above its intended duty or undersized conductors.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A short circuit occurs when a fault drastically reduces the impedance of the current path. Current can rise very quickly and produce severe thermal and mechanical effects.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The thermomagnetic circuit breaker must address both situations. The thermal part acts against overloads. The magnetic part acts against high currents typical of short circuits.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">What does a thermomagnetic circuit breaker protect?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">A thermomagnetic circuit breaker primarily protects conductors and the circuit against overcurrents. It helps reduce the risks of excessive heating, insulation degradation, connection damage, short-circuit faults and propagation of thermal effects.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">It also enables circuit switching, meaning it can be used to energize and de-energize the protected section, provided its characteristics and intended use are respected.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">In an electrical panel, a thermomagnetic circuit breaker can protect lighting circuits, socket-outlets, dedicated equipment, feeders, small motors and specific circuits according to the design.<\/p>\n\n\n\n\n<h2 class=\"wp-block-heading\">What does a thermomagnetic circuit breaker not protect against?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">A thermomagnetic circuit breaker does not replace all other protective devices.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">By itself, it is not an RCD. Therefore, it should not be confused with residual-current protection against electric shock and leakage currents. It is also not an SPD, meaning it does not protect the installation against transient overvoltages of atmospheric or switching origin.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">In addition, a thermomagnetic circuit breaker does not correct a poorly designed installation. If conductors are unsuitable, the curve is wrong, breaking capacity is insufficient or devices are not coordinated, simply installing a circuit breaker does not solve the technical problem.<\/p>\n\n\n\n<div class=\"wp-block-a3a-destaque\">\n\n<p class=\"wp-block-paragraph\"><strong>A thermomagnetic circuit breaker does not replace an RCD or an SPD<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Overcurrent protection, residual-current protection and surge protection perform different functions. To explore surge protection further, see <a href=\"\/conteudo\/artigos-tecnicos\/dps-o-que-e-e-como-instalar\/\">SPD: surge protection, NBR 5410, LPS and grounding<\/a>.<\/p>\n\n<\/div>\n\n\n\n<h2 class=\"wp-block-heading\">Relationship between thermomagnetic circuit breakers and B, C and D curves<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">B, C and D curves are associated with the circuit breaker&#8217;s magnetic behavior. They indicate the range of multiples of rated current in which the device tends to operate rapidly.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A Type B thermomagnetic breaker operates magnetically at lower currents. Type C requires a higher current for magnetic operation. Type D tolerates still higher peaks before magnetic operation.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">This difference is essential for loads with starting current. Motors, transformers, compressors, electronic power supplies and certain equipment can present transient peaks at energization. The curve must allow normal starting without compromising short-circuit protection.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Therefore, breaker curve selection should not be based on habit. It should be defined from the load, starting current, circuit length, minimum short-circuit current and coordination with other devices.<\/p>\n\n\n\n\n<h2 class=\"wp-block-heading\">Single-pole, two-pole and three-pole thermomagnetic circuit breakers<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Thermomagnetic circuit breakers can also be classified by number of poles.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A single-pole thermomagnetic circuit breaker operates on one pole. It is common in single-phase circuits according to the supply arrangement and applicable isolation criteria.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A two-pole thermomagnetic circuit breaker operates on two poles simultaneously. It may be applied to line-to-line or line-to-neutral circuits according to the installation, voltage and isolation requirements.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A three-pole thermomagnetic circuit breaker operates on three poles and is common in three-phase circuits. It is applied in feeders, motors, machines, distribution boards and electrical panels.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The number of poles should be selected considering the supply system, protected circuit, earthing arrangement, need to disconnect live conductors and safety and maintenance requirements.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">DIN-rail thermomagnetic circuit breaker and miniature circuit breaker<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">A DIN-rail thermomagnetic circuit breaker is the modular type installed on DIN rail and widely used in low-voltage distribution boards. It appears in residential, commercial and building installations and in many final circuits.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The term \u201cminiature circuit breaker\u201d usually refers to compact modular breakers, normally used at lower currents and in distribution boards. Despite the commercial terminology, technical specification still requires appropriate rated current, curve, breaking capacity, number of poles, voltage and compliance with the applicable product standard.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">In larger installations such as main low-voltage switchboards, industrial panels and higher-current feeders, molded-case circuit breakers or other devices with different characteristics and capabilities may be used.<\/p>\n\n\n\n\n<h2 class=\"wp-block-heading\">Thermomagnetic circuit breaker for electric showers<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Searches for thermomagnetic circuit breakers for electric showers are common, but this application should not be resolved using only a generic current table.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The shower circuit must consider equipment power, voltage, design current, conductor cross-section, installation method, voltage drop, temperature, grouping, distance and applicable protection requirements.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Increasing the breaker rated current to prevent tripping may leave conductors inadequately protected. The correct approach is to verify whether the circuit was sized for the actual load and whether the breaker is compatible with the conductors and installation.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Thermomagnetic circuit breaker for air-conditioning<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Air-conditioning equipment may have significant starting current, especially compressors and non-inverter equipment. Even modern equipment may have specific energization characteristics due to internal electronics.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Circuit-breaker selection should consider manufacturer data, operating current, starting current, trip curve, conductors, distance and installation method.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">In commercial and building installations, multiple HVAC units may require simultaneity analysis, circuit distribution and coordination within the electrical panel.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Thermomagnetic circuit breakers for motors<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Motors can have starting currents several times higher than rated current. Therefore, motor protection should not be treated as an ordinary circuit without assessing starting method, mechanical load, operating duty and specific protection.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">In many cases, motor circuit breakers, contactors, thermal overload relays and coordinated protection schemes are used. The thermomagnetic circuit breaker can form part of the protection, but its function must be clearly defined in the design.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The critical point is to ensure that protection allows normal motor starting without nuisance tripping while still operating safely during short circuits and abnormal conditions.<\/p>\n\n\n\n\n<h2 class=\"wp-block-heading\">Difference between a thermomagnetic circuit breaker and an RCD<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">A thermomagnetic circuit breaker protects against overcurrents, namely overloads and short circuits. An RCD operates on residual currents, which may indicate leakage to earth or a risk of electric shock.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">They perform different functions. A standard thermomagnetic breaker does not replace an RCD. Likewise, an RCD without integral overcurrent protection must be protected by a suitable device against short circuits and overloads according to the circuit arrangement.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">There is also the RCBO, which combines residual-current protection with overcurrent protection in a single device. Even so, its application must comply with the product standard, NBR 5410 and the electrical design.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Difference between a thermomagnetic circuit breaker and an SPD<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">An SPD protects against transient overvoltages. It is used to limit voltage surges caused by switching operations, indirect lightning effects or events associated with the electrical system.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A thermomagnetic circuit breaker does not perform this function. It operates on overcurrent. In many panels, the SPD must be coordinated with an overcurrent protective device, which may be a circuit breaker or fuse specified according to manufacturer instructions and installation conditions.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">This means circuit breakers, RCDs and SPDs perform complementary roles. A well-designed electrical installation treats these devices as part of a protection system rather than as isolated components.<\/p>\n\n\n\n<div class=\"wp-block-a3a-destaque\">\n\n<p class=\"wp-block-paragraph\"><strong>Circuit-breaker specification should appear in the electrical design<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Rated current, curve, number of poles and breaking capacity must be consistent with conductors, load and short-circuit current. To see how this appears in technical documentation, see <a href=\"\/conteudo\/artigos-tecnicos\/projetos-eletricos-baixa-tensao-etapas-normas-recomendacoes-2\/\">Low-Voltage Electrical Designs<\/a>.<\/p>\n\n<\/div>\n\n\n\n\n<h2 class=\"wp-block-heading\">What does NBR 5410 say about thermomagnetic circuit breakers?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">NBR 5410 addresses circuit breakers within the topic of overcurrent protection. The standard requires live conductors to be protected against overloads and short circuits by automatic disconnection devices, except for specific exceptions.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The standard also establishes that overload protection and short-circuit protection must be coordinated. This is directly related to the thermomagnetic circuit breaker because it combines thermal and magnetic operation.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">When addressing the nature of protective devices, NBR 5410 cites circuit breakers in accordance with applicable product standards such as ABNT NBR 5361, ABNT NBR IEC 60947-2, ABNT NBR NM 60898 and IEC 61009-2-1. In other words, the installation must comply with NBR 5410, while the device must also comply with the corresponding product standard.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Coordination between conductors and the thermomagnetic circuit breaker<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Overload protection requires compatibility among design current, device rated current and conductor current-carrying capacity.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">In practice, the breaker should not be selected with a rated current above the permissible capacity of the cables merely to avoid tripping. This can expose conductors to improper heating.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Installation method, circuit grouping, ambient temperature, insulation type, conductor cross-section and voltage drop must also be considered.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Breaking capacity of the thermomagnetic circuit breaker<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Breaking capacity indicates the short-circuit current the circuit breaker can safely interrupt under the conditions established by the manufacturer and product standard.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Two thermomagnetic circuit breakers with the same rated current and the same curve can have different breaking capacities. Therefore, saying \u201c32 A Type C thermomagnetic circuit breaker\u201d is still not a complete specification.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">In panels close to the origin of the installation, transformers, main feeders and main low-voltage switchboards, prospective short-circuit current can be high. In these cases, breaking capacity is a decisive criterion.<\/p>\n\n\n\n\n<h2 class=\"wp-block-heading\">How to specify a thermomagnetic circuit breaker in electrical design<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Specification of a thermomagnetic circuit breaker should follow a technical sequence.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">First, identify the load and the purpose of the circuit. Then calculate design current and size conductors according to installation method, voltage drop and actual installation conditions.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Next, define circuit-breaker rated current, trip curve, number of poles, breaking capacity, operating voltage and applicable product standard.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Minimum and maximum short-circuit current, selectivity with upstream and downstream devices, compatibility with RCDs and SPDs, and maintenance and operation requirements must also be assessed.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Common mistakes when selecting a thermomagnetic circuit breaker<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">The most common mistakes are:<\/p>\n\n\n\n<ul class=\"wp-block-list\"><li>selecting only by amperage;<\/li><li>increasing rated current to avoid tripping;<\/li><li>ignoring the trip curve;<\/li><li>ignoring breaking capacity;<\/li><li>using Type C as a universal default;<\/li><li>replacing with Type D without checking minimum short-circuit current;<\/li><li>confusing a thermomagnetic circuit breaker with an RCD;<\/li><li>assuming the circuit breaker replaces the SPD;<\/li><li>installing a device incompatible with the load;<\/li><li>not updating the single-line diagram after panel changes.<\/li><\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">These mistakes can cause nuisance trips, inadequate protection, conductor overheating, equipment failures, maintenance risks and documentation nonconformity.<\/p>\n\n\n\n\n<h2 class=\"wp-block-heading\">When should specialized engineering be engaged?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Specialized engineering is recommended for new designs, renovations, load expansions, panel replacement, installation of motors, transformers, air-conditioning, electrical panels, main low-voltage switchboards, recurring trips, component overheating or missing up-to-date electrical documentation.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">It is also recommended when compliance with NBR 5410 is required, when a single-line diagram must be prepared, or when electrical inspection, a technical report, protection review, short-circuit analysis or device coordination is needed.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Technical analysis makes it possible to verify whether the installed thermomagnetic circuit breaker is compatible with the circuit, whether conductors are protected, whether breaking capacity is sufficient and whether the installation is consistent with the electrical design.<\/p>\n\n\n\n<div class=\"wp-block-a3a-destaque\">\n\n<p class=\"wp-block-paragraph\"><strong>Deepen your knowledge of thermal operation, magnetic operation and sizing<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A thermomagnetic circuit breaker must be assessed together with the load, cables, curve, breaking capacity and selectivity. See the white paper <a href=\"\/conteudo\/whitepapers\/whitepaper-metodo-especificacao-dimensionamento-disjuntores-baixa-tensao\/\">Method for Specification and Sizing of Circuit Breakers in Low-Voltage Electrical Installations<\/a> and explore the relationship with grounding and equipotential bonding in the eBook <a href=\"\/conteudo\/ebooks\/aterramento-eletrico\/\">Electrical Grounding: Fundamentals, Design and Standardization<\/a>.<\/p>\n\n<\/div>\n\n\n\n\n<h2 class=\"wp-block-heading\">Conclusion<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">The thermomagnetic circuit breaker is one of the most common devices in low-voltage electrical installations, but its application requires technical criteria. It combines thermal operation for overloads and magnetic operation for high currents such as short circuits.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Its selection should not be based only on rated current. Correct specification involves the load, conductors, trip curve, number of poles, breaking capacity, prospective short-circuit current, selectivity and coordination with RCDs, SPDs and other protective devices.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">When treated as part of the electrical design, the thermomagnetic circuit breaker contributes to a safer, documented installation that is compatible with standards requirements. When treated as a simple replacement part, it can mask problems and compromise circuit protection.<\/p>\n\n\n\n<details class=\"wp-block-details is-layout-flow wp-block-details-is-layout-flow\"><summary>Technical references<\/summary>\n\n<p class=\"wp-block-paragraph\">[1] ASSOCIA\u00c7\u00c3O BRASILEIRA DE NORMAS T\u00c9CNICAS. <a href=\"https:\/\/www.abntcatalogo.com.br\/\" target=\"_blank\" rel=\"noopener noreferrer\">ABNT NBR 5410 \u2014 Low-voltage electrical installations<\/a>. Consult the ABNT Catalog to confirm the current edition and amendments.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">[2] ASSOCIA\u00c7\u00c3O BRASILEIRA DE NORMAS T\u00c9CNICAS. ABNT NBR NM 60898 \u2014 Circuit-breakers for overcurrent protection for household and similar installations.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">[3] INTERNATIONAL ELECTROTECHNICAL COMMISSION. <a href=\"https:\/\/webstore.iec.ch\/en\/publication\/66269\" target=\"_blank\" rel=\"noopener noreferrer\">IEC 60898-1:2015+AMD1:2019 \u2014 Circuit-breakers for overcurrent protection for household and similar installations<\/a>.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">[4] ASSOCIA\u00c7\u00c3O BRASILEIRA DE NORMAS T\u00c9CNICAS. ABNT NBR IEC 60947-2 \u2014 Low-voltage switchgear and controlgear \u2014 Circuit-breakers.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">[5] INTERNATIONAL ELECTROTECHNICAL COMMISSION. <a href=\"https:\/\/webstore.iec.ch\/en\/publication\/66277\" target=\"_blank\" rel=\"noopener noreferrer\">IEC 60947-2:2024 \u2014 Low-voltage switchgear and controlgear \u2014 Part 2: Circuit-breakers<\/a>.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">[6] ASSOCIA\u00c7\u00c3O BRASILEIRA DE NORMAS T\u00c9CNICAS. ABNT NBR 5361 \u2014 Low-voltage circuit breakers.<\/p>\n\n<\/details>\n\n\n\n<details class=\"wp-block-details is-layout-flow wp-block-details-is-layout-flow\"><summary>Frequently asked questions<\/summary>\n<div class=\"schema-faq wp-block-yoast-faq-block\"><div class=\"schema-faq-section\" id=\"faq-question-o-que-disjuntor-termomagn-tico-b03fc96d\"><strong class=\"schema-faq-question\">What is a thermomagnetic circuit breaker?<\/strong> <p class=\"schema-faq-answer\">A thermomagnetic circuit breaker is a protective device that combines thermal operation against overloads and magnetic operation against high currents such as short circuits.<\/p><\/div><div class=\"schema-faq-section\" id=\"faq-question-para-que-serve-um-disjuntor-termomagn-tico-a07299e7\"><strong class=\"schema-faq-question\">What is a thermomagnetic circuit breaker used for?<\/strong> <p class=\"schema-faq-answer\">It protects electrical circuits against overcurrents by interrupting the supply when current exceeds the limits established for the circuit.<\/p><\/div><div class=\"schema-faq-section\" id=\"faq-question-como-funciona-a-atua-o-t-rmica-do-disjuntor-0c0f8c4b\"><strong class=\"schema-faq-question\">How does thermal operation work?<\/strong> <p class=\"schema-faq-answer\">Thermal operation responds to heating caused by overload. The higher the current above the permissible value, the shorter the operating time tends to be.<\/p><\/div><div class=\"schema-faq-section\" id=\"faq-question-como-funciona-a-atua-o-magn-tica-do-disjuntor-d671e77c\"><strong class=\"schema-faq-question\">How does magnetic operation work?<\/strong> <p class=\"schema-faq-answer\">Magnetic operation responds rapidly to high currents normally associated with short circuits or intense current peaks.<\/p><\/div><div class=\"schema-faq-section\" id=\"faq-question-qual-a-diferen-a-entre-disjuntor-t-rmico-e-magn--82206aae\"><strong class=\"schema-faq-question\">What is the difference between thermal and magnetic operation?<\/strong> <p class=\"schema-faq-answer\">Thermal operation responds to heating and protects against overload. Magnetic operation responds to an electromagnetic field and to high currents of short duration.<\/p><\/div><div class=\"schema-faq-section\" id=\"faq-question-disjuntor-termomagn-tico-protege-contra-choque-e-101b2561\"><strong class=\"schema-faq-question\">Does a thermomagnetic circuit breaker protect against electric shock?<\/strong> <p class=\"schema-faq-answer\">Not directly. Electric-shock protection involves specific measures such as grounding, equipotential bonding and RCDs where applicable.<\/p><\/div><div class=\"schema-faq-section\" id=\"faq-question-disjuntor-termomagn-tico-substitui-dr-0f5da11b\"><strong class=\"schema-faq-question\">Does a thermomagnetic circuit breaker replace an RCD?<\/strong> <p class=\"schema-faq-answer\">No. A thermomagnetic circuit breaker protects against overcurrents. An RCD operates on residual currents and has a different function.<\/p><\/div><div class=\"schema-faq-section\" id=\"faq-question-disjuntor-termomagn-tico-substitui-dps-75e47cb3\"><strong class=\"schema-faq-question\">Does a thermomagnetic circuit breaker replace an SPD?<\/strong> <p class=\"schema-faq-answer\">No. An SPD protects against transient overvoltages. A thermomagnetic circuit breaker operates against overcurrents.<\/p><\/div><div class=\"schema-faq-section\" id=\"faq-question-o-que-significa-disjuntor-termomagn-tico-curva-c-44255d41\"><strong class=\"schema-faq-question\">What does Type C thermomagnetic circuit breaker mean?<\/strong> <p class=\"schema-faq-answer\">It means the breaker has thermal and magnetic operation, with a Type C magnetic curve that tolerates moderate starting currents before instantaneous operation.<\/p><\/div><div class=\"schema-faq-section\" id=\"faq-question-como-escolher-um-disjuntor-termomagn-tico-6ec3ab92\"><strong class=\"schema-faq-question\">How should a thermomagnetic circuit breaker be selected?<\/strong> <p class=\"schema-faq-answer\">Selection should consider design current, conductors, trip curve, breaking capacity, number of poles, voltage, short-circuit current and coordination with other devices.<\/p><\/div><div class=\"schema-faq-section\" id=\"faq-question-posso-aumentar-a-amperagem-do-disjuntor-para-par-3b63e637\"><strong class=\"schema-faq-question\">Can I increase the circuit-breaker amperage to stop it from tripping?<\/strong> <p class=\"schema-faq-answer\">Not without technical analysis. Increasing rated current can leave conductors inadequately protected and mask an overload or circuit fault.<\/p><\/div><div class=\"schema-faq-section\" id=\"faq-question-qual-a-diferen-a-entre-disjuntor-monopolar-bipol-525efba0\"><strong class=\"schema-faq-question\">What is the difference between single-pole, two-pole and three-pole circuit breakers?<\/strong> <p class=\"schema-faq-answer\">The difference is the number of poles disconnected. A single-pole breaker operates one pole, a two-pole breaker two poles and a three-pole breaker three poles, the latter being common in three-phase circuits.<\/p><\/div><\/div>\n<\/details>\n\n\n\n<details class=\"wp-block-details is-layout-flow wp-block-details-is-layout-flow\"><summary>Additional technical materials<\/summary>\n<h3 class=\"wp-block-heading\">Related solutions<\/h3>\n<ul class=\"wp-block-list\"><li><a href=\"\/solucoes\/engenharia-eletrica\/infraestrutura-eletrica-de-baixa-tensao\/\">Low-Voltage Electrical Infrastructure<\/a><\/li><li><a href=\"\/solucoes\/engenharia-eletrica\/qgbt-paineis-eletricos-baixa-tensao\/\">Main Low-Voltage Switchboards and Low-Voltage Electrical Panels<\/a><\/li><li><a href=\"\/solucoes\/engenharia-eletrica\/seguranca-eletrica-adequacao-nr-10\/\">Electrical Safety and NR-10 Compliance<\/a><\/li><\/ul>\n<h3 class=\"wp-block-heading\">Related engineering services<\/h3>\n<ul class=\"wp-block-list\"><li><a href=\"\/servicos\/planejamento\/projeto-eletrico-baixa-tensao\/\">Low-Voltage Electrical Design<\/a><\/li><li><a href=\"\/servicos\/servicos-transversais\/estudo-curto-circuito-seletividade-coordenacao-protecoes\/\">Short-Circuit, Selectivity and Protection Coordination Study<\/a><\/li><li><a href=\"\/servicos\/levantamento-e-diagnostico\/inspecao-instalacoes-eletricas\/\">Electrical Installation Inspection<\/a><\/li><li><a href=\"\/servicos\/servicos-transversais\/comissionamento-aceite-instalacoes-eletricas\/\">Commissioning and Technical Acceptance of Electrical Installations<\/a><\/li><\/ul>\n<h3 class=\"wp-block-heading\">Related technical content<\/h3>\n<ul class=\"wp-block-list\"><li><a href=\"\/conteudo\/artigos-tecnicos\/disjuntores-baixa-tensao-tipos-funcao-especificacao\/\">Low-Voltage Circuit Breakers<\/a><\/li><li><a href=\"\/conteudo\/artigos-tecnicos\/curvas-disjuntores-curva-b-c-d\/\">Circuit-Breaker Trip Curves: B, C and D<\/a><\/li><li><a href=\"\/conteudo\/artigos-tecnicos\/capacidade-interrupcao-disjuntores-icu-ics-curto-circuito-presumido\/\">Breaking Capacity: Icu and Ics<\/a><\/li><li><a href=\"\/conteudo\/artigos-tecnicos\/seletividade-disjuntores-o-que-e-como-funciona-baixa-tensao\/\">Circuit-Breaker Selectivity<\/a><\/li><li><a href=\"\/conteudo\/artigos-tecnicos\/como-dimensionar-disjuntores-baixa-tensao-corrente-curva-ka-seletividade\/\">How to size circuit breakers<\/a><\/li><li><a href=\"\/conteudo\/artigos-tecnicos\/disjuntor-dr-idr-ddr-diferencas-funcao-quando-usar\/\">RCD, RCCB and RCBO<\/a><\/li><li><a href=\"\/conteudo\/artigos-tecnicos\/dimensionamento-cabos-eletricos\/\">Electrical Cable Sizing<\/a><\/li><\/ul>\n<h3 class=\"wp-block-heading\">Guides and references<\/h3>\n<ul class=\"wp-block-list\"><li><a href=\"\/conteudo\/guias-tecnicos\/guia-completo-sobre-instalacoes-eletricas-de-baixa-tensao\/\">Complete Guide to Low-Voltage Electrical Installations<\/a><\/li><li><a href=\"\/conteudo\/whitepapers\/whitepaper-metodo-especificacao-dimensionamento-disjuntores-baixa-tensao\/\">Method for Specification and Sizing of Circuit Breakers<\/a><\/li><li><a href=\"\/conteudo\/artigos-tecnicos\/ensaios-eletricos-nbr-5410\/\">Electrical Tests and Final Verification under NBR 5410<\/a><\/li><\/ul>\n<\/details>\n","protected":false},"excerpt":{"rendered":"<p>Understand what a thermomagnetic circuit breaker is, how thermal and magnetic operation works, which applications require attention and how to specify it according to NBR 5410.<\/p>\n","protected":false},"author":1,"featured_media":78665,"parent":0,"template":"","meta":{"_a3a_global_related_solutions":[],"_a3a_global_related_services":[],"_a3a_global_related_materials":[],"_a3a_post_lang":"en-us","_a3a_translation_group_id":"6212cc72-877b-49bc-b976-50a063626afa","_a3a_i18n_canonical_slug":"thermomagnetic-circuit-breaker-how-it-works-when-to-use","_a3a_prod_post_id":"","_a3a_lang_url_en-us":"","_a3a_lang_url_es-es":""},"categories":[],"segments":[],"mercados":[],"etapas":[],"class_list":["post-83290","articles","type-articles","status-publish","has-post-thumbnail","hentry"],"_links":{"self":[{"href":"https:\/\/a3aengenharia.com\/en-us\/wp-json\/wp\/v2\/articles\/83290","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/a3aengenharia.com\/en-us\/wp-json\/wp\/v2\/articles"}],"about":[{"href":"https:\/\/a3aengenharia.com\/en-us\/wp-json\/wp\/v2\/types\/articles"}],"author":[{"embeddable":true,"href":"https:\/\/a3aengenharia.com\/en-us\/wp-json\/wp\/v2\/users\/1"}],"version-history":[{"count":1,"href":"https:\/\/a3aengenharia.com\/en-us\/wp-json\/wp\/v2\/articles\/83290\/revisions"}],"predecessor-version":[{"id":83296,"href":"https:\/\/a3aengenharia.com\/en-us\/wp-json\/wp\/v2\/articles\/83290\/revisions\/83296"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/a3aengenharia.com\/en-us\/wp-json\/wp\/v2\/media\/78665"}],"wp:attachment":[{"href":"https:\/\/a3aengenharia.com\/en-us\/wp-json\/wp\/v2\/media?parent=83290"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/a3aengenharia.com\/en-us\/wp-json\/wp\/v2\/categories?post=83290"},{"taxonomy":"segments","embeddable":true,"href":"https:\/\/a3aengenharia.com\/en-us\/wp-json\/wp\/v2\/segments?post=83290"},{"taxonomy":"mercados","embeddable":true,"href":"https:\/\/a3aengenharia.com\/en-us\/wp-json\/wp\/v2\/mercados?post=83290"},{"taxonomy":"etapas","embeddable":true,"href":"https:\/\/a3aengenharia.com\/en-us\/wp-json\/wp\/v2\/etapas?post=83290"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}