Where should the temperature fuse be installed? Comprehensive installation specifications and practical guide for all scenarios

 

Thermal fuses (thermal cutoffs) serve as the final safety safeguard against overheating in household appliances, industrial equipment, and power supplies; more than 90% of their protective effectiveness depends on whether they are installed in compliance with relevant standards. Whether it’s appliance repair technicians replacing components, DIY enthusiasts tuning equipment, R&D engineers designing products, or production staff performing batch assembly, they all face a core question: Where exactly should a thermal fuse be placed to ensure compliance? And why does improper installation lead to frequent blowouts—or even complete failure of the protection, potentially resulting in fires?

 

Article Content Navigation

1. Where should the temperature fuse be installed? Overview of General Standards and Key Conclusions

2. Wiring specification for the temperature fuse: requirements for live/neutral wires and series/parallel connection

3. Precise Instructions on Standard Installation Locations for Temperature Fuses in Mainstream Home Appliances and Equipment

4. Core Judgment Principles and Underlying Logic for Selecting the Installation Location of the Temperature Fuse

5. Detailed requirements for the contact distance between the temperature fuse and the heat source, as well as installation methods.

6. Safety Compliance Standards and Boundary Requirements for the Installation Location of Temperature Fuses

7. Risks Associated with Improper Installation of Temperature Fuses and How to Avoid Common Installation Pitfalls

8. Layout Rules for Multiple Temperature Fuse Units in the Same Equipment and Fault Location Adjustment Plan

9. FAQ on High-Frequency Issues

 

1: Where should the temperature fuse be installed? Overview of General Standards and Core Conclusions

This chapter focuses on users’ fragmented information-retrieval needs—specifically, obtaining core answers within three seconds. It begins by presenting authoritative, general conclusions to address the pervasive pain points of information fragmentation and the lack of standardized guidelines across the web, while aligning with the fast-paced, skimming habits of all user groups.

 

1.1 Core Authoritative Conclusion on the Installation Location of the Temperature Fuse

General installation rules for global safety standard harmonization: The thermal fuse must be connected in series within the live power supply circuit of the heating element being protected, and its body must be in direct, close contact with the core heat source to be protected, with no insulating barriers or obstructions, to ensure the fastest and most accurate detection of any abnormal temperature rise in the protected component.

This is the primary guideline for the installation location of thermal fuses: all equipment and all application scenarios must adhere to this core rule when determining installation points. Any deviation will result in failure of protection and non-compliance with safety regulations.

1.2 Priority Ranking of Temperature Fuse Installation Locations

Based on protective effectiveness and compliance with safety regulations, the installation locations are prioritized as follows, from highest to lowest; these priorities can be directly applied:

First priority (optimal): Directly attach to the metal surface of the protected core’s heat-generating component, securing it in the hottest zone of the heat source and connecting it in series within that component’s dedicated live-power supply circuit.

Second priority (qualified): Embedded in the end gaps of protected windings (motors, transformers), in direct contact with the heating windings, and connected in series within the winding’s live-supply circuit;

Third priority (restricted use): Must be mounted on a dedicated thermally conductive bracket fixed to the heat source, with no thermal insulation or shielding between the bracket and the heat source; the maximum gap shall not exceed 0.5 mm. This option is applicable only in special structural scenarios where direct contact is not feasible.

Strictly prohibited: installation in a suspended state, installation far from heat sources, installation with thermal insulation wrapping, connection solely in series on the neutral line, and parallel installation. Any of these practices will directly render the protective function completely ineffective and constitute a critical safety violation subject to an immediate veto.

 

1.3 Core Reminder for Repair and Replacement

When replacing or repairing temperature fuses in household appliances and equipment, it is imperative to install them strictly at the original factory-specified mounting locations; any unauthorized relocation of the fuse is strictly prohibited. The factory-specified locations have been validated through safety certification and temperature-rise testing as the optimal positions; relocating the fuse arbitrarily can result in failure of the protective function, frequent false tripping, and even safety hazards.

 

2. Wiring specification for the temperature fuse: requirements for live/neutral wires and series/parallel connection

This chapter focuses on users’ most fundamental questions about wiring location identification, clarifies the core wiring rules, and addresses the root causes of protection failure and electric shock risks resulting from incorrect wiring. It is designed to meet the practical needs of maintenance technicians, DIY enthusiasts, and production operators.

 

2.1 Core rule for series/parallel wiring configuration: Wiring must be 100% in series; parallel connections are strictly prohibited.

Core mandatory rules: The thermal fuse must be connected in series throughout the power supply circuit of the protected component; parallel installation is strictly prohibited, as is bypassing it across the terminals of a switch or thermostat.

Compliant series connection logic: The thermal fuse is a single-use, irreversible overheat protection device. When connected in series within the circuit, once it reaches its rated operating temperature and blows, it completely disconnects power to the protected component, thereby providing overheat protection. This is the only compliant wiring method.

The fatal hazard of parallel connection: When components are connected in parallel, even after the thermal fuse blows, current can still flow through the parallel circuit, continuously powering and heating the protected components. As a result, the overheat protection is completely disabled, inevitably leading to dry-burn and fire hazards—making this an absolutely prohibited and unsafe practice.

Supplementary Specification: In multi-circuit equipment, each independent heating element must be individually connected in series with its corresponding thermal fuse. It is strictly prohibited for multiple heating elements to share a single thermal fuse connected in series within the main circuit; otherwise, a protection blind spot will arise where an individual element overheats while the main-circuit fuse fails to detect the fault.

 

2.2 Core Rule for Live/Neutral Wire Connection: Prioritize series connection on the live side; connecting only to the neutral wire is strictly prohibited.

Core mandatory rules: The thermal fuse must be connected in series on the live (L) conductor of the protected circuit. For Class I household appliances and industrial equipment, it is strictly prohibited to rely solely on connecting the thermal fuse in series on the neutral (N) conductor as the sole overheat protection.

Core advantages of fire-line-side installation: The thermal fuse is connected in series on the live wire, and once it blows, it completely disconnects the energized side of the protected component. Under fault or maintenance conditions, the component remains entirely de-energized, thereby fundamentally eliminating the risk of electric shock while also complying with the mandatory requirements of general household appliance safety standards such as GB 4706 and IEC 60335.

Fatal hazards of connecting only to the neutral wire: When connected solely in series on the neutral side, even after the thermal fuse blows, the protected component remains energized and connected to the live wire, resulting in full-line voltage. Maintenance personnel may mistakenly assume the equipment is de-energized and, upon contact, are highly likely to suffer an electric shock. Furthermore, this configuration fails to meet safety standards, rendering the product ineligible for 3C, UL, and other certifications; should a safety incident occur, the manufacturer will bear full legal liability.

Supplementary specifications for special applications: In the safety protection design for bipolar disconnection, a temperature fuse of the same specification may be connected in series on both the live and neutral lines; however, the live-line side must serve as the primary protective element, and its actuation temperature shall not exceed that of the neutral-line side. In low-voltage DC circuits, the fuse must be connected in series on the positive terminal; upon fusing, it shall disconnect the high-voltage side, thereby enhancing safety.

 

2.3 Auxiliary Specifications for Wiring Locations

The wiring connection of the thermal fuse must be located as close as possible to the power supply terminal of the protected component, thereby minimizing the length of live circuitry remaining energized after the fuse blows and reducing the risk of short circuits and electric shock.

Lead wires must be sleeved with high-temperature, flame-retardant tubing, and wiring terminals must be securely crimped or soldered to prevent poor contact that could cause localized heating and unintended fuse operation.

During soldering, the lead must be held with tweezers to dissipate heat; the soldering temperature should not exceed 300°C, and the soldering time should not exceed 3 seconds, to prevent excessive heat from conducting into the fuse body and causing premature failure of the internal temperature-sensing element.

 

3: Precise Instructions on Standard Installation Locations for Temperature Fuses in Mainstream Home Appliances and Equipment

This section presents the page’s core, high-value, and high-weight content, addressing the primary needs of maintenance personnel—who account for the largest share of traffic—by providing manufacturer-standard installation locations for each appliance model. These precise, actionable guidelines directly support on-site operations and resolve key questions that arise during repair and parts replacement. All recommended installation locations comply with the original-equipment assembly specifications of leading domestic brands such as Midea, Joyoung, Supor, and Gree, as well as with IEC, UL, and GB safety standards.

 

3.1 Standard Installation Locations for Kitchen Heating Appliances

This category of home appliances has the highest demand for thermal fuse replacements and is also the most common type of equipment encountered in repair scenarios. The original manufacturer’s installation locations are as follows:

Rice cooker / Electric pressure cooker

Original factory-standard mounting location: tightly adjacent to the metal bottom surface of the heating plate, securely fastened within a dedicated plastic or metal retaining slot at the center of the heating plate, connected in series within the heating plate’s live-power supply circuit, and wired in series with the main temperature controller.

Additional note: Installation on the motherboard or control panel is strictly prohibited; the heating element must be in direct contact with the heating plate. For the heat-preserving heating element on the lid of an electric pressure cooker, a separate temperature fuse must be provided and installed in close proximity to the heating element, connected in series on the live wire side of the heat-preserving circuit.

Electric Kettle / Health-Preserving Pot

Original factory-standard mounting location: the metal surface of the heating plate directly adjacent to the bottom of the kettle, secured within a dedicated clip on the edge of the heating plate, connected in series within the live wire circuit of the heating plate, and in series with the bimetal thermostat.

Additional note: The device must be installed inside the kettle body and must never be mounted on the power board of the base. This ensures accurate detection of the heating plate temperature during dry-boil operation, thereby preventing the kettle from catching fire due to dry boiling.

Induction cooker / Electric ceramic cooker

Original factory-standard sensing points: There are two primary sensing locations. ① The center of the coil disc, with the thermistor holder tightly mounted against the coil disc and connected in series within the coil disc’s power supply circuit; ② On the heat sink of the IGBT power module, in direct contact with the metal surface of the heat sink and connected in series on the live input side of the entire unit, serving as a fail-safe protection measure.

Additional note: The temperature fuses at the two locations are rated for different operating temperatures—130°C to 155°C for the coil winding and 185°C for the IGBT heat sink. Interchanging their positions or mixing their ratings is strictly prohibited.

Microwave oven / Light-wave oven

Original factory-standard placement points: There are two core locations. ① On the heat sink of the magnetron, in direct contact with the metal surface of the heat sink and connected in series within the magnetron’s power supply circuit; ② On the cavity wall at the top of the oven cavity, in direct contact with the metal cavity wall and connected in series on the live wire side of the unit’s main power input, serving as a fail-safe overheat protection for the cavity.

 

3.2 Standard Installation Locations for Personal Care and Environmental Heating Appliances

Hair dryer / Heat gun / Hair curling iron

Original factory-standard mounting position: the front end of the mica sheet bracket, which is tightly adjacent to the heating wire (heating element), located between the air inlet and the heating wire, with no airflow duct obstruction, and connected in series within the live-power supply circuit of the heating wire.

Additional note: Installation on the handle or circuit board is strictly prohibited. The temperature fuse must be positioned so that it remains unobstructed from the heating element, ensuring that it can promptly detect temperature rise and trip in the event of dry operation or blockage of the air inlet. Furthermore, in the motor circuit of high-power hair dryers, temperature fuses must never be used as a substitute for current fuses.

Electric heater / Heating appliance / Oil-filled radiator

Original factory-standard installation locations: For PTC and electric heating tube models, the device shall be mounted at the metal casing end directly adjacent to the heating element, connected in series within the live wire circuit of the heating element, and positioned away from direct airflow from the cooling air duct. For oil-filled radiators, the device shall be mounted at the wiring terminals of the electric heating tube and securely fixed to the metal inner tank wall; installation inside the control panel on the outer casing is strictly prohibited.

Additional note: For electric heaters with multiple heating elements, each heating element must be equipped with a separate temperature fuse, which is to be connected in series within its corresponding circuit.

Air conditioner / Wall-mounted unit

Original factory-standard installation locations: There are two core locations: ① At the end of the heating element of the indoor unit’s PTC electric auxiliary heater, in close contact with the metal surface and connected in series within the live wire circuit of the electric auxiliary heating system; ② Inside the outdoor unit’s compressor terminal box, in close contact with the end cover of the compressor windings and connected in series within the compressor power supply circuit.

 

3.3 Standard Installation Locations for Motors, Transformers, and Power Supply Equipment

Motor products (fan motors, washing machine motors, air conditioner compressors, servo motors)

Original factory-standard placement: closely adjacent to the end turns of the motor stator windings, embedded in the insulation gaps between the windings, or secured to the metal end shields of the windings with high-temperature-resistant cable ties, and connected in series within the motor’s power supply circuit.

Additional note: The device must be in direct contact with the windings to accurately sense the internal temperature rise of the windings. In the event of inter-turn short circuits or overloads, the windings may overheat even if the circuit current does not exceed the rated limit; in such cases, conventional current fuses will fail to trip. Only a temperature-sensing fuse that is tightly attached to the windings can provide effective protection.

Transformer types (power-frequency transformers, high-frequency transformers, power adapters)

Original factory-standard installation location: directly adjacent to the transformer core surface or to the end of the primary winding, connected in series within the transformer’s primary-side live-line input circuit.

Additional note: Installation on the PCB board at a location far from the transformer is strictly prohibited. The device must be directly in contact with the core or windings to ensure accurate temperature-rise detection and immediate tripping in the event of transformer overload or turn-to-turn short circuit.

Switch-mode power supplies / Inverters / UPS power supplies

Original factory-standard placement: directly adjacent to the metal heat-sink surfaces of the power-switching transistor, high-frequency transformer, and PFC inductor, connected in series on the live-line side of the primary input of the power supply, serving as a fail-safe over-temperature protection for the entire unit.

Additional note: For multi-output power supplies, each high-voltage heating circuit must be equipped with a dedicated thermal fuse, which shall be installed on the corresponding heating component.

 

4. Core Judgment Principles and Underlying Logic for Selecting the Installation Location of the Temperature Fuse

This chapter focuses on uncovering users’ deep-seated, latent needs and deconstructs the core decision-making logic for determining installation locations. It addresses the pain point that, after upgrading devices or in non-standard scenarios, users are unable to independently identify the correct mounting points, thereby delivering replicable and transferable value that meets the personalized adaptation requirements of R&D engineers, maintenance technicians, and DIY enthusiasts.

The core function of a thermal fuse is to provide ultimate overheat protection in fault conditions. The sole guiding principle for selecting its installation location is to ensure that the fuse can detect abnormal temperature rises in the protected component as quickly and accurately as possible, thereby promptly opening the circuit before the temperature reaches a safety threshold and preventing safety incidents. All selection of installation locations must adhere to the following five core principles:

 

4.1 Heat Source Priority Principle: First priority is to position the device as close as possible to the core heat-generating component being protected.

This is the highest-priority core principle among all principles and directly determines the effectiveness of protection.

Underlying principle: The triggering condition for a thermal fuse is temperature, not current. Only when the fuse is in direct, close contact with the core heat source being protected can it detect abnormal temperature rises with zero delay and promptly blow before the temperature exceeds the safety threshold.

Practical installation guidelines: Whenever protecting a specific component, the thermal sensor must be mounted in close contact with that component; under no circumstances should it be installed “within the circuit but far from the heat source.” For example, when protecting a heating plate, the sensor must be affixed directly to the heating plate—never mounted on the motherboard. The normal temperature difference between the motherboard and the heating plate can exceed 50°C, and under abnormal dry-burn conditions this difference can soar to 200°C, which may prevent the fuse from blowing altogether and thereby trigger a fire.

Boundary requirements: The maximum gap between the fuse and the heat source shall not exceed 0.5 mm, and any thermal insulation medium is strictly prohibited.

 

4.2 Circuit Priority Principle: Must be connected in series within the dedicated power supply circuit of the protected component.

Underlying principle: The thermal fuse must precisely disconnect power to the faulty component to prevent the fault from spreading, while ensuring that the faulty component is de-energized after the fuse blows.

Practical operating rules: ① For equipment with a single heating element, the temperature fuse shall be connected in series within the live-supply circuit of the heating element, as close as possible to the supply end of the element; ② For equipment with multiple heating elements, each independent heating circuit must be equipped with its own dedicated temperature fuse, connected in series within the corresponding circuit; sharing a single fuse for multiple circuits is strictly prohibited; ③ It is strictly forbidden to connect the fuse in series within a circuit that is unrelated to the protected component.

 

4.3 Safety-First Principle: Prioritize connecting the live wire side; after fusing, disconnect the energized terminal.

Underlying logic: The core requirement of safety standards is to eliminate the risk of electric shock under fault conditions while ensuring reliable disconnection of the circuit.

Practical operating rules: ① For AC circuits, the fuse must be connected in series on the live side; it is strictly prohibited to connect it solely on the neutral side as the sole protective measure. ② For DC circuits, the fuse must be connected in series on the positive terminal side; it is strictly prohibited to connect it solely on the negative terminal side. ③ The installation location must ensure that, after the fuse blows, the electrical clearance and creepage distance comply with safety regulations, thereby preventing arcing and short circuits.

 

4.4 Principle of No Interference: Avoid interference from non-protected heat sources, cooling air ducts, and low-temperature zones.

Underlying principle: A thermal fuse can only sense the temperature at its own location; any external interference will cause the sensed temperature to deviate from the actual temperature of the protected component, leading to false tripping or failure of protection.

Operational guidelines: ① The installation location must be kept at a safe distance from other non-protective heating components to prevent heat from these sources from causing unintended fuse blowout; ② Installation directly in the path of cooling fan airflow or ducts is strictly prohibited, as the cooling effect of the airflow may cause the fuse to register a lower-than-actual temperature, resulting in failure to trip during abnormal overheating; ③ Installation in low-temperature zones of the equipment or on the enclosure’s control panel—areas where the temperature difference from heat sources is excessively large—is also strictly forbidden, to avoid delayed protection.

 

4.5 Maintainability Principle: Balancing Protective Performance with Ease of Replacement

Underlying principle: A thermal fuse is a one-time-use, fusible device that must be replaced after a fault occurs. Its installation location must balance maintainability with the requirement to ensure effective protection.

Practical Implementation Rules: ① The installation location must be easily accessible for disassembly and replacement; it must not be sealed within a closed cavity that cannot be opened. ② Sufficient lead wire length must be reserved to prevent solder joints from coming loose or wiring from being damaged due to pulling during replacement. ③ The mounting method must strike a balance between secure fixation and ease of removal; snap-fit fasteners and cable ties should be preferred over irreversible adhesives that result in permanent attachment.

 

5. Detailed requirements for the contact distance between the temperature fuse and the heat source, as well as installation methods.

This chapter focuses on combined surface-and-depth-level requirements, specifying detailed criteria for mating distance, mounting methods, and insulation protection to address issues such as inadvertent tripping, delayed protection, and device failure caused by ambiguities in installation positioning. It is designed to meet the practical operational and design implementation needs of production operators, maintenance personnel, and R&D engineers.

 

5.1 Adhesion Distance and Core Specifications for Thermal Conductive Media

Core mandatory requirements: The temperature fuse must be in direct, tight contact with the metal surface of the protected heat source, with no insulating medium present; the maximum gap between the fuse and the surface shall not exceed 0.5 mm. Suspended mounting, air-gap mounting, or mounting with insulating wraps is strictly prohibited.

Optimal bonding solution: Ensure that the temperature-sensing area of the fuse body is in 100% surface-to-surface contact with the metal heat source, and securely fasten it using high-temperature-resistant metal clips or stainless steel cable ties to eliminate any looseness or gaps. A high-thermal-conductivity silicone grease (thermal conductivity ≥ 1.2 W/m·K) may be applied to the bonding interface to fill microscopic gaps and enhance thermal conductivity; under no circumstances should insulating or thermally isolating silicone sealant or ordinary adhesives be used as substitutes.

Maximum allowable clearance: the mating gap must not exceed 0.5 mm. Test data show that when the gap exceeds 0.5 mm, thermal conduction efficiency drops by more than 50%, and in the event of abnormal overheating, the fuse blow-out delay exceeds 30 seconds, greatly increasing the risk of dry burning and fire. When the gap exceeds 2 mm, thermal conduction essentially ceases, and the fuse loses its protective function entirely.

Prohibited Conduct:

It is strictly prohibited to install a fuse by wrapping its temperature-sensing element with insulating materials such as electrical tape, heat-shrink tubing, plastic components, or mica sheets, even if the wrap fits perfectly, as this will completely block thermal conduction.

Suspension installation is strictly prohibited; if the fuse is more than 1 cm away from the heat source, it will be completely unable to detect the heat source temperature.

Installation in the low-temperature edge zones of heat sources is strictly prohibited; sensors must be installed in the highest-temperature zones of the heat source, such as the center of the heating plate, the ends of motor windings, and the core heating regions of heat sinks.

 

5.2 Installation and Fixing Specifications for Different Scenarios

Different heat-source types require different compliance-based mounting methods, which must be strictly adhered to in order to ensure secure attachment and effective thermal conduction:

Metal planar heat sources (heating plates, heat sinks, inner liner walls)

Compliance-based fixing methods: Use original manufacturer–specified metal clips, stainless steel hose clamps, or high-temperature cable ties to secure the fuse body, ensuring full contact with the metal surface, with no warping and no gaps. The use of plastic cable ties or ordinary adhesives is strictly prohibited, as plastic ties will melt and fall off at high temperatures, while ordinary adhesives can form an insulating layer that compromises heat conduction.

Winding-type heat sources (motor and transformer windings)

Compliance-based fixing method: Wrap the fuse body with a high-temperature, flame-retardant insulating sleeve (with a temperature rating of ≥200°C), then embed it in the gap at the winding end, ensuring direct contact with the enameled wire. Secure it using high-temperature glass-fiber binding tape to ensure accurate detection of the winding’s internal temperature rise. It is strictly prohibited to fix the fuse solely to the winding’s outer casing or support structure, as this would create an insulating layer between the fuse and the winding.

Heating wire / heating element-type heat sources (hair dryers, hot air guns)

Compliance-based fixing method: Secure the device using a high-temperature-resistant ceramic bracket, ensuring that the fuse body is in close contact with the mica sheet support of the heating element and that the distance between the fuse and the heating wire does not exceed 2 mm. There should be no obstruction in the airflow path to ensure direct detection of the heating element’s radiative temperature. Installation downstream of the airflow duct is strictly prohibited to prevent airflow-induced cooling from compromising temperature-sensing accuracy.

Surface-mount temperature fuse for PCB boards

Compliance-based mounting method: Solder the component directly onto the PCB in close proximity to the heat-generating device, ensuring that the solder pad is electrically and thermally connected to the device’s heat sink so that heat is conducted through the PCB copper foil. Soldering at a location far from the heat-generating device is strictly prohibited to ensure an unobstructed thermal path via the copper foil.

 

5.3 Detailed Requirements for Lead Wire and Insulation Protection

Lead length : Sufficient lead wire allowance must be provided to ensure that, after installation, the fuse body is free of stress and will not loosen or detach due to pulling or vibration; at the same time, the leads must not be excessively long to prevent contact with nearby energized components and subsequent short-circuiting.

Insulation Protection : Only the leads and pins of the fuse shall be insulated with high-temperature, flame-retardant sleeving; the fuse’s temperature-sensing element must never be covered. The clearances between the installation location and any adjacent live parts shall be no less than 3 mm for 220 V AC circuits and no less than 8 mm for high-voltage circuits to prevent arcing and short circuits.

Welding and Crimping Specifications : During manual soldering, the lead wire must be held by tweezers at its root (close to the body) to facilitate heat dissipation; the soldering temperature should not exceed 300°C, and the soldering time should not exceed 3 seconds, to prevent excessive heat from conducting into the body and causing premature failure of the internal temperature-sensing element. When crimping terminals, a dedicated crimping tool must be used to ensure a secure crimp, thereby avoiding poor contact that can lead to localized heating and unintended tripping.

 

6. Safety Compliance Standards and Boundary Requirements for the Installation Location of Temperature Fuses

This chapter focuses on deep-rooted, latent compliance needs and core regulatory requirements, systematically reviewing the mandatory installation-location requirements stipulated in globally applicable safety standards. It defines compliance boundaries and prohibited practices, addresses the compliance verification and product certification needs of R&D, safety-testing, and manufacturing personnel, and helps avoid product certification failures and large-scale compliance risks.

The installation location of the temperature fuse must strictly comply with the following globally recognized safety standards: IEC 60691 (the international standard for thermal fuses), UL 1020 (the North American safety standard for thermal fuses), GB 9816.1-2013 (the Chinese national standard for thermal fuses, which is equivalent to IEC 60691), and GB 4706.1-2005 (the general safety standard for household and similar electrical appliances).

 

6.1 Mandatory Compliance Requirements for Installation Location under Safety Standards

Mandatory requirements for temperature-sensing accuracy (IEC 60691, Chapter 8; GB 9816.1, Chapter 8)

The installation location must ensure that the thermal fuse accurately senses the temperature rise of the protected component. Under standard fault test conditions, the deviation between the device’s actual operating temperature and its nominal rated operating temperature shall not exceed ±5°C; furthermore, any deviation in operating temperature caused by the installation method or location shall not exceed ±3°C. Failure to comply with these requirements will result in non-compliance with safety regulations, and the product will be ineligible for certification.

Mandatory requirements for circuit disconnection (GB 4706.1, Chapter 24; UL 1020, Chapter 9)

As an overheat protection device for fault conditions, the thermal fuse must reliably disconnect the power supply to the protected component. For Class I contact-type household appliances and industrial equipment, the live (L) conductor must be prioritized for disconnection; it is strictly prohibited to rely solely on disconnecting the neutral (N) conductor as the sole overheat protection measure. After fusing, the circuit-breaking point must meet the electrical clearance requirements corresponding to the rated voltage: for 220 V AC circuits, the electrical clearance shall be ≥3 mm and the creepage distance ≥4 mm, to prevent arcing and re-ignition following fuse operation.

Mandatory requirements for fixed reliability (Chapter 10 of GB 9816.1 and Chapter 10 of IEC 60691)

The temperature fuse must be securely installed and fixed. Under normal equipment operation, as well as during transportation, vibration, and drop tests, it must not become loose, displaced, or fall off; it must maintain close contact with the heat source at all times to ensure stable actuation temperature. The use of easily melted or easily detached fastening methods, such as ordinary plastic cable ties or low-temperature adhesives, is strictly prohibited.

Mandatory environmental adaptability requirements (UL 1020, Chapter 7; IEC 60691, Chapter 9)

The installation location must be protected from direct exposure to moisture, corrosive gases, oil contamination, and dust; otherwise, device sealing may fail, the temperature-sensing element may age, and the actuation characteristics may drift. In humid environments or for outdoor equipment, a waterproof thermal fuse must be selected and installed in a sealed enclosure with an IP rating that matches the operating conditions, to ensure long-term operational stability.

Fail-Safe Mandatory Requirements (Chapter 19 of GB 4706.1)

The installation location must ensure that, upon fusible temperature fuse operation, no other safety hazards are triggered, such as exposed live parts, insulation failure, short circuits, or fire; installation in locations where fusible temperature fuse operation would cause the plastic housing to melt or expose combustible materials to direct heat is strictly prohibited.

 

6.2 Prohibitive Installation Standards Subject to Safety Regulation Veto

The following installation methods are expressly prohibited by safety regulations and will result in failure of product certification; furthermore, any safety incidents arising therefrom shall entail full legal liability.

Installation is strictly prohibited in locations with thermal insulation where the temperature of the protected component cannot be accurately sensed.

It is strictly prohibited to connect a thermal fuse solely in series on the neutral line as the equipment’s sole overheat protection device.

It is strictly prohibited to install a thermal fuse in parallel or to bypass the switch or thermostat, as this will prevent the circuit from being disconnected after the fuse blows.

It is strictly prohibited to install the device in locations where the ambient temperature exceeds the device’s holding temperature (Th) during normal operation, as this can lead to long-term high-temperature aging and unintended fuse blowout.

Installation in locations where the post-fuse electrical clearance and creepage distance are insufficient is strictly prohibited to prevent arcing and short circuits.

It is strictly prohibited to permanently and irreversibly seal a thermal fuse within a sealed enclosure in such a way that it cannot be disassembled or replaced.

 

7: Risks of Improper Installation Location for Temperature Fuses and How to Avoid Common Installation Mistakes

This chapter focuses on the core risk-avoidance needs common to all user groups, identifies the key risks arising from incorrect installation locations, dissects prevalent installation misconceptions across the network and their corresponding mitigation strategies, addresses users’ multifaceted decision-making concerns, and aligns with the safe-operation requirements of all user segments.

 

7.1 Classification of Core Risk Levels Due to Improper Installation Location

Risk Level	Risk Consequences	Core Cause (Improper Installation Location)
Fatal Risk	Complete failure of the overheating protection results in equipment burnout and fire hazards, for which legal liability shall be borne.	Installation away from heat sources, with thermal insulation wrapping, suspended mounting, and parallel connection can result in the fuse failing to blow when abnormal overheating occurs.
High-risk hazard	Electrical shock accidents and personal injury during maintenance	If it is connected only in series on the neutral side, the protected equipment will still be energized on the live wire even after the fuse blows, increasing the risk of electric shock if accidentally touched during maintenance.
Medium risk	Frequent, irregular false tripping leads to equipment malfunction and increased maintenance costs.	Installation in close proximity to unprotected heat sources, enclosed high-temperature zones with poor heat dissipation, or locations where the normal operating temperature exceeds the device’s rated holding temperature can accelerate component aging and cause malfunctions.
Low risk	Early aging-induced device failure leads to a sharp decline in lifespan.	When the installation location is exposed to high-temperature conditions for an extended period, exceeding the specified operating temperature, the internal temperature-sensing element gradually ages, leading to drift in actuation characteristics and eventual failure.
Compliance Risk	Product certification failed, market regulatory penalties imposed, and a mass recall initiated.	Installation locations that do not comply with safety standards—such as wiring only to the neutral conductor, insecure mounting, or insufficient electrical clearances—can result in failure of 3C/UL certification and subsequent penalties after product launch.

 

7.2 Common Installation Pitfalls Across the Network and How to Avoid Them

Misconception 1: “As long as it’s connected in the circuit, it doesn’t matter where it’s installed.”

Correction: A thermal fuse is a temperature-triggered device, not a current-triggered one. When installed in the circuit but positioned away from the heat source, it cannot detect abnormal temperature rises in the protected component at all, rendering overheat protection 100% ineffective. It is imperative to strictly adhere to the “heat-source-first” principle and mount the thermal fuse directly adjacent to the core heat-generating component being protected; this is the sole prerequisite for effective protection.

Misconception #2: “It doesn’t matter whether it’s installed on the neutral or live wire—as long as it can break the circuit, that’s fine.”

Correction: If the fuse is installed only on the neutral side, the protected equipment will remain connected to the live conductor even after the fuse blows, resulting in a fully energized circuit at all times. This poses an extremely high risk of electric shock during maintenance and also fails to meet safety regulations, making it a disqualifying issue. The fuse must be installed in series on the live side to ensure that, once it blows, the protected equipment is completely de-energized.

Misconception 3: “Wrapping with insulating tape to secure the connection prevents short circuits and makes it safer.”

Correction: Insulating tape and heat-shrink tubing both serve as thermal insulation materials. When used to wrap the body of a fuse, they completely block heat conduction, preventing the fuse from detecting the temperature of the heat source. As a result, the fuse will fail to blow during abnormal overheating, thereby creating an even greater safety hazard. Insulation should be applied only to the lead wires; the temperature-sensing portion of the fuse body must remain in direct contact with the heat source, and any form of thermal insulation wrapping is strictly prohibited.

Misconception 4: “Mount it next to the cooling fan to cool the fuse and prevent accidental blowing.”

Correction: Direct airflow from the cooling fan can cause the fuse’s temperature to remain far below the actual temperature of the protected heat source. In the event of abnormal overheating, the heat source may already have reached a dangerous temperature while the fuse has not yet reached its tripping threshold, thereby completely losing its protective function. It is essential to avoid positioning the cooling airflow directly on the fuse to ensure that the temperature sensed by the fuse accurately reflects the heat source’s actual temperature.

Misconception 5: “If a device has multiple heat-generating components, it’s sufficient to install only one thermal fuse at the main power inlet.”

Correction: The thermal fuse at the main power inlet can only monitor the temperature at the power supply inlet and cannot detect abnormal temperature rises in individual heating components. For example, if the heating plate overheats and reaches 300°C while the power inlet temperature remains only 80°C, the thermal fuse will not trip, potentially leading to a fire. Therefore, each independent heating component must be equipped with its own dedicated thermal fuse, installed in close proximity to its respective heat source.

Misconception 6: “During repair, if the original factory mounting location can’t be found, just pick any spot and secure it there.”

Correction: The original factory-installed fuse location has been optimized through temperature-rise testing and safety-certification verification; any unauthorized modification can result in protection failure and frequent nuisance tripping. During maintenance or replacement, the fuse must be installed strictly at the original factory position. Even if the lead wires are too short, they must be replaced with fuses of the same specification and length; arbitrary relocation of the fuse is strictly prohibited.

 

8. Layout Rules for Multiple Temperature Fuse Units on the Same Equipment and Fault Location Adjustment Plan

This chapter focuses on deep-level and latent derivative composite requirements, clarifies the layout rules for multi-temperature fuses in the same equipment, and provides troubleshooting and positional adjustment solutions for failures caused by improper installation. It is designed to meet the needs of R&D engineers and maintenance personnel for root-cause failure elimination and solution optimization.

 

8.1 Core Rules for the Layout of Multi-Temperature Fuse Links in the Same Equipment

High-power, multi-functional equipment typically incorporates multiple thermal fuses; the following layout guidelines must be followed to ensure comprehensive protection with no blind spots, coordinated tripping without overreach, and full compliance with safety regulations:

Principle of Independent Layout for Each Circuit

Each independent heating circuit and heating component must be equipped with its own dedicated temperature fuse, which is connected in series within the respective live-power supply circuit. It is strictly prohibited to share a single fuse among multiple components. For example, an electric rice cooker has three heating components: a bottom heating plate, an upper-lid insulation pad, and side insulation strips. Each of these components must have its own temperature fuse installed, with the fuse tightly positioned against the corresponding heat source and connected in series within its dedicated circuit. When a single component overheats, only that circuit is disconnected, leaving the other components operating normally while accurately pinpointing the fault location.

Priority-Based Hierarchical Layout Principle

Based on the fault risk level, a two-tier protection scheme is implemented to establish a comprehensive overheat protection system:

Secondary partition protection: Each heat-generating component is equipped with a dedicated thermal fuse whose actuation temperature is matched to the component’s maximum allowable operating temperature, ensuring it trips first and serving as the primary safeguard.

Primary backup protection: installed in series on the main live input side of the entire unit, directly adjacent to the core component that generates the highest heat. Serving as the final line of defense against overheating, its tripping temperature is 10°C to 20°C higher than that of the secondary protection and is activated only in extreme scenarios where the secondary protection has failed.

Temperature Gradient Matching Principle

The operating temperature of each fuse must be set according to the thermal tolerance limit of the protected component, with a reasonable temperature gradient; it is strictly prohibited to use the same temperature rating for all fuses. For example, the heating element of a hair dryer has a thermal tolerance of 200°C, so a secondary protection fuse rated at 185°C should be used; a motor has a thermal tolerance of 130°C, so a secondary protection fuse rated at 115°C should be used; and a primary protection fuse rated at 200°C should be used for overall system-level backup protection. This ensures that components with lower thermal tolerance operate first, high-risk components are protected as a last resort, and there are no overrating or protection blind spots.

Principle of Non-Interference Layout

Sufficient clearance must be maintained between multiple fuses to prevent heat generated by the operation of one fuse from affecting the operating characteristics of others; each fuse must be positioned directly adjacent only to its own protected heat source and kept away from other heat sources to avoid cross-interference that could lead to unintended fusing. For example, the fuse for a transformer must be spaced at least 5 cm from the fuse for the heating plate to prevent heat from the heating plate from causing the transformer fuse to operate erroneously.

Principles for Safety Compliance Planning

All fuses must be connected in series on the live side; once a fuse blows, the corresponding circuit will be de-energized. Between the energized parts of multiple fuses, electrical clearances and creepage distances that meet the rated voltage requirements must be maintained to prevent short circuits. All installation locations must comply with safety standards, ensuring secure mounting and accurate temperature sensing.

 

8.2 Troubleshooting and Position Adjustment Plan for Failures Caused by Improper Installation Location

For the three most common types of faults encountered during maintenance and commissioning, standardized troubleshooting procedures and adjustment plans are provided, enabling direct implementation to thoroughly eliminate the faults.

 

8.2.1 Fault 1: The temperature fuse frequently blows randomly without any overheating fault in the equipment.

Primary root cause: improper installation location—either in an unprotected high-temperature zone or subject to interference from other heat sources—resulting in prolonged operating temperatures exceeding the device’s rated holding temperature and leading to aging-induced false tripping.

Troubleshooting and Adjustment Steps:

Step 1: During full-load operation, use a thermometer to measure the actual temperature at the fuse mounting location and compare it with the hold temperature (Th) specified in the device datasheet. If the measured temperature exceeds the hold temperature, it can be confirmed that the issue lies with the mounting location.

Step 2: Verify whether the installation location is near transformers, power transistors, or other heat-generating components; whether it is in a sealed, non-ventilated high-temperature zone; and whether it is subject to thermal radiation from other heat sources.

Step 3: Position Adjustment Plan: ① Relocate the installation to a position away from non-protected heat sources, ensuring that the ambient temperature at the installation location remains at least 10°C below the set operating temperature during normal operation; ② Ensure that the fuse is in direct thermal contact with the protected heat source and is not subject to interference from other heat sources; ③ Optimize equipment heat dissipation by increasing ventilation openings and installing cooling fans to reduce the internal chamber temperature; ④ If relocation is not feasible, and provided that safety compliance verification has been successfully completed, replace the fuse with one having a higher actuation temperature while maintaining compatibility with the original holding temperature; arbitrary replacement is strictly prohibited.

Step 4: Verify the adjustment effect: Operate the equipment at full load for 4 consecutive hours; measure the fuse temperature, which should remain stable below the rated operating temperature, with no abnormal overheating or blowing, thereby completely eliminating the fault.

 

8.2.2 Fault 2: Equipment dry-burning and overheating, with the thermal fuse failing to blow and protection ineffective.

Primary root cause: The installation location is far from the heat source, equipped with thermal insulation, and exposed to direct airflow from the duct, resulting in ineffective heat conduction and preventing the fuse from detecting abnormal temperature rises at the heat source.

Troubleshooting and Adjustment Steps:

Step 1: De-energize and disassemble the device; verify that the installation location is sufficiently distant from the protected heat source, is enclosed by an insulating layer, and is mounted in a suspended configuration. Use a thermal imager to simulate dry-burn conditions, measuring both the temperature of the heat source and the body temperature of the fuse. If the temperature difference exceeds 20°C, it can be confirmed that thermal conduction has failed.

Step 2: Check whether insulating materials such as electrical tape, heat-shrink tubing, and plastic components are wrapping the device body, and whether the device is installed in a position directly in the path of the cooling fan’s airflow, resulting in an abnormally low fuse temperature.

Step 3: Position Adjustment Plan: ① Remove all thermal insulation wraps, then mount the fuse body directly and tightly against the metal surface of the protected heat source, securing it with metal clips; ensure the maximum gap does not exceed 0.5 mm, and apply high-thermal-conductivity silicone grease to enhance thermal conductivity; ② Relocate the installation position to avoid direct airflow from the cooling duct, placing the fuse in the hottest zone of the heat source to ensure unobstructed exposure and no air-flow-induced cooling; ③ Replace the fuse with a long-leaded version to ensure it can be properly aligned with the core heating area of the heat source, thereby preventing installation-position deviation caused by insufficient lead length.

Step 4: Verify the adjustment effect: Perform a standard dry-burn test. When the heat source temperature reaches the rated operating temperature, the fuse shall blow within the specified time, thereby breaking the circuit and restoring normal protection functionality.

 

8.2.3 Fault 3: Multi-fuse protection equipment experiences over-level tripping and false operations.

Primary root causes: improper temperature gradient settings and cross-interference at installation locations, resulting in low-risk circuits tripping first or non-protective circuits tripping erroneously.

Troubleshooting and Adjustment Steps:

Step 1: Verify the operating temperature and installation location of each thermal fuse, and check whether the temperature gradient has been set incorrectly. For example, if the operating temperature of the primary protection in the main circuit is lower than that of the secondary protection in the branch circuits, the main circuit may trip before the branch circuits have operated.

Step 2: Check whether the fuse has been installed in an incorrect location, too close to other high-temperature heat sources, causing it to overheat and inadvertently blow.

Step 3: Layout Adjustment Plan: ① Reconfigure the temperature gradient so that the tripping threshold for secondary branch-circuit protection is 10°C to 20°C lower than that for primary main-circuit protection, thereby ensuring priority operation in the event of a branch-circuit fault; ② Adjust the installation position of each fuse so that it is placed directly adjacent to its own protected heat source and kept well away from other heat sources, thus preventing cross-interference; ③ Verify the tripping temperature of each fuse to ensure precise matching with the temperature tolerance limit of the protected component—neither too high nor too low.

Step 4: Verify the adjustment effectiveness: Simulate an overheat fault in each circuit to confirm that the corresponding fuse operates with priority, with no overreach tripping or nuisance tripping, thereby ensuring the protection system is functioning properly.

 

Frequently Asked Questions

 

Question: Must the thermal fuse be in direct contact with the heat source? Is it acceptable to install it at a distance?

Answer: The temperature fuse must be installed in direct contact with the heat source; installation with any air gap is strictly prohibited. The operating principle of a temperature fuse relies on temperature detection; an air gap significantly reduces thermal conduction efficiency, preventing timely melting during abnormal overheating and rendering the protective function completely ineffective. For compliant installation, the maximum allowable gap between the fuse and the heat source shall not exceed 0.5 mm, with 100% surface-to-surface contact being the optimal mounting configuration.

 

Question: Should the thermal fuse be installed on the live wire or the neutral wire? What is the difference?

Answer: The fuse must be connected in series on the live (phase) side; it is strictly prohibited to connect it solely on the neutral side as the sole protective measure. When installed on the live side, a blown fuse will completely disconnect the energized terminals of the protected equipment, eliminating the risk of electric shock during maintenance and ensuring compliance with global safety standards. In contrast, if the fuse is installed only on the neutral side, the protected equipment will remain connected to the live conductor even after the fuse blows, leaving the entire circuit energized at all times and creating a high risk of electric shock—such an arrangement constitutes a critical violation that would result in immediate rejection under safety regulations.

 

Question: When repairing or replacing a temperature fuse, is it permissible to change its installation location?

Answer: No, it is not permitted. The original factory-installed mounting location has been certified for safety compliance and validated through temperature-rise testing as the optimal placement. Any unauthorized modification may result in loss of protective function, frequent false tripping, or even safety incidents. During maintenance or replacement, the fuse must be installed strictly at the original factory location; if the lead wires are insufficient, replace the fuse with one of the same specifications and longer lead wires. Unauthorized relocation is strictly prohibited.

 

Question: Can a temperature fuse be wrapped with electrical tape?

Answer: Insulating tape may only be used to insulate the leads and pins; it is strictly prohibited to wrap the temperature-sensing element of the fuse itself. Insulating tape acts as a thermal barrier, and wrapping it over the fuse body will completely block heat conduction, preventing the fuse from detecting the temperature of the heat source. As a result, the fuse will fail to blow during abnormal overheating, potentially leading to serious safety hazards such as fires.

 

Question: For equipment with multiple heat-generating components, is it sufficient to install only a single thermal fuse?

Answer: No. Each independent heating element must be equipped with its own dedicated thermal fuse, mounted in close proximity to the respective heat source and connected in series within the corresponding circuit. Installing only a single fuse in the main circuit will fail to detect abnormal temperature rises in individual components, potentially leading to overheating and dry operation of those components while the fuse remains inactive. This completely compromises protection and greatly increases the risk of safety incidents.

 

Question: Is it acceptable to install the thermal fuse next to the cooling air duct?

Answer: Installation directly in the path of cooling fan airflow or ductwork is strictly prohibited. Direct airflow can cause the thermal fuse to sense a temperature far lower than the actual temperature of the protected heat source; when an abnormal overheating condition occurs, the heat source may already have reached a hazardous temperature while the thermal fuse has not yet reached its actuation threshold, thereby completely losing its protective function. It is essential to avoid areas directly exposed to duct airflow to ensure that the temperature sensed by the thermal fuse accurately reflects the actual temperature of the heat source.

 

A comprehensive, multi-dimensional analysis of the entire text reveals that the core principles governing the installation location of thermal fuses consistently revolve around three fundamental pillars: precise temperature sensing, reliable circuit interruption, and compliance with safety regulations. Whether in product design, mass production, maintenance and replacement, or DIY troubleshooting, it is imperative to strictly adhere to the basic rules of “positioning the fuse in close proximity to the primary heat source, connecting it in series within the live wire circuit, and ensuring compliance with relevant safety standards.” By rigorously avoiding all common installation pitfalls and violations, the thermal fuse can truly fulfill its role as a fail-safe overheat protection device, serving as the final line of defense for both equipment and personal safety.