Editorial Technical Reference

Thermal Disconnector

This page explains how Thermal Disconnector is classified within Electrical Equipment Manufacturing. Technical values and manufacturer relationships are research references; confirm the current specification and supplier evidence for each order.

Technical Definition & Core Assembly

A safety component within a Surge Protection Device (SPD) that automatically disconnects the circuit when excessive heat is detected, preventing fire hazards.

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Thermal Disconnector in a manufacturing environment
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Product Specifications

Technical details and manufacturing context for Thermal Disconnector

Definition
A thermal disconnector is a critical safety component integrated into Surge Protection Devices (SPDs). Its primary function is to monitor the temperature of the SPD's metal oxide varistor (MOV) or other surge-arresting elements. If these components overheat due to sustained overvoltage, repeated surges, or end-of-life failure, the thermal disconnector activates. It physically and permanently opens the electrical circuit, disconnecting the failed SPD from the power line. This action prevents the overheated components from causing a fire, smoke, or damage to the surrounding equipment, thereby ensuring the safety of the electrical installation. The thermal disconnector is designed for use in low-voltage SPDs, with typical rated voltages of 230/400 V AC and, for photovoltaic applications, 500–1000 V DC. It handles rated currents from 16 to 63 A and has a breaking capacity of 10–50 kA, ensuring it can interrupt prospective short-circuit currents. The response time is ≤0.1 seconds to quickly disconnect before overheating escalates. Operating temperatures range from -40 to 85°C, suitable for outdoor use. The device uses a low-melting-point solder alloy (e.g., tin-bismuth) as a thermal trigger, with a trip temperature of 120–150°C. The housing is made of flame-retardant thermoplastic (UL94 V-0), and the degree of protection ranges from IP20 to IP65 depending on the enclosure. Insulation resistance is ≥100 MΩ at 500 V DC, and dielectric strength is 2.5–4 kV. The weight varies from 50 to 150 g. These parameters are typical reference ranges; actual values must be confirmed with the manufacturer for the specific model and application. The thermal disconnector is a passive component that requires no external power and provides a visible indication (often a colored flag) when tripped. It is a one-time device; once activated, it must be replaced. Proper selection involves verifying rated voltage, current, breaking capacity, and thermal trip temperature against the SPD's specifications and the installation's requirements. Regular inspection should check for the indicator flag and ensure no signs of overheating or damage.
Working Principle
The thermal disconnector contains a low-melting-point solder or a thermally sensitive mechanical latch. Under normal operating temperatures, this element holds the electrical contacts closed. When the monitored temperature exceeds a predetermined threshold (e.g., due to MOV overheating), the solder melts or the latch releases. This action is triggered by conducted heat from the surge-arresting element. The release mechanism, often spring-loaded, then forces the electrical contacts apart, creating a permanent open circuit and providing a visible indication (often a colored flag) of disconnection.
Common Materials
Low-melting-point solder alloy (e.g., tin-bismuth), Spring steel, High-temperature plastic housing, Copper or brass contacts
Technical Parameters
ParameterTypical rangeNotes & selection driver
Rated Voltage230/400 V ACTypical for low-voltage SPDsIEC 61643-1
Rated Current16–63 ADepends on SPD rating
Breaking Capacity10–50 kAMust exceed prospective short-circuit currentIEC 60947-2
Response Time≤0.1 sFast disconnection to prevent overheating
Operating Temperature-40–85 °CExtended range for outdoor useIEC 60068-2-1
Rated Voltage (DC)500–1000 V DCFor PV applicationsIEC 61643-31
Insulation Resistance≥100 MΩAt 500 V DC
Dielectric Strength2.5–4 kVWithstands impulse voltageIEC 60243-1
Thermal Trip Temperature120–150 °CMelting point of fusible alloy
Housing MaterialUL94 V-0Flame-retardant thermoplasticUL 94
Degree of ProtectionIP20–IP65IP65 for outdoor enclosuresIEC 60529
Weight50–150 gVaries with current rating

Ranges are indicative industry figures for RFQ preparation, not a supplier commitment. Confirm every value and standard with the legal manufacturer before ordering.

Components / BOM
  • Thermal Sensor / Fusible Alloy Part
    Melts at a specific temperature to initiate the disconnection sequence.
    Material: Low-melting-point solder alloy
  • Contact Mechanism Part
    Provides the electrical connection path; forced open upon activation.
    Material: Copper or brass
  • Spring Actuator
    Stores mechanical energy to rapidly separate the contacts when released.
    Material: Spring steel
  • Housing / Insulation Part
    Provides electrical insulation, contains components, and may offer visual trip indication.
    Material: High-temperature plastic (e.g., PBT)

Application & selection

Application Fit & Sizing Matrix

Operational Limits
pressure: Atmospheric pressure only (non-pressurized component)
other spec: Current rating: 10A to 100A, Voltage rating: Up to 600V AC/DC, Response time: <5 seconds at threshold temperature
temperature: Operating range: -40°C to +85°C, Trip threshold: 85°C to 120°C (adjustable)
Media Compatibility
✓ Electrical enclosures with air cooling ✓ Dry, indoor industrial environments ✓ Surge Protection Devices in commercial power distribution
Unsuitable: High humidity or corrosive atmospheres without proper IP rating
Sizing Data Required
  • Maximum continuous current (A)
  • System voltage rating (V)
  • Ambient operating temperature range (°C)

Risk, maintenance & compliance

Reliability & Engineering Risk Analysis

Failure Mode & Root Cause
Thermal Element Fatigue
Cause: Repeated thermal cycling from frequent overloads or short circuits causing metal fatigue in the bimetallic strip or solder pot, leading to premature tripping or failure to trip.
Contact Degradation
Cause: Arcing during disconnection causing pitting, welding, or oxidation of electrical contacts, resulting in increased resistance, overheating, or failure to open properly.
Maintenance Indicators
  • Visible discoloration, scorching, or melting on the thermal disconnector housing indicating overheating
  • Audible buzzing, crackling, or intermittent tripping without apparent overload
Engineering Tips
  • Ensure proper sizing and coordination with circuit protection devices to prevent unnecessary thermal cycling from frequent low-level overloads
  • Implement regular infrared thermography inspections to detect abnormal heating patterns before catastrophic failure occurs

Indicative industry ranges for design and RFQ preparation. Confirm the exact figures and applicable standard with the manufacturer before specifying.

Compliance & Manufacturing Standards

Applicable Standards
ISO 13849-1: Safety of machinery - Safety-related parts of control systems ANSI/UL 60730-1: Automatic electrical controls for household and similar use DIN EN 60947-4-1: Low-voltage switchgear and controlgear - Contactors and motor-starters

Quoted from the published standard.

Manufacturing Precision
  • Actuation temperature: +/-2°C
  • Contact gap: +/-0.1mm
Quality Inspection
  • Thermal cycling test
  • Dielectric strength test
Technical documentation
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Manufacturers of Thermal Disconnector

3 companies list this product among what they make. Company figures are quoted from each company's own website; every card states where the relationship came from.

Dongguan Senreach Electronics Co., Ltd.
Guangdong, CN
Also makes: Circuit Breaker, Circuit Breaker / Fuse Holder, Energy Storage/Transfer Element (for active systems)
Listed on the company's own website · profile compiled by CNFX from public sources
Listed there as: “Thermal Fuses”
View source page ↗ senreach.com · recorded 2026-09-05
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RHT
Ningbo, Zhejiang, CN
Also makes: Feed-through Terminal Blocks, High-Frequency Transformer, Current Transformer and 9 more
Listed on the company's own website · profile compiled by CNFX from public sources
Listed there as: “- Thermal fuses”
View source page ↗ rhtecp.com · recorded 2026-09-14
View profile Send enquiry
Sino-Cool Refrigeration Parts Industry Co., Ltd.
Xiamen, Fujian, CN
Also makes: Temperature Controller, Expansion Valve, Mechanical Seal and 9 more
Listed on the company's own website · profile compiled by CNFX from public sources
Listed there as: “Thermal Fuse”
View source page ↗ sino-cool.com · recorded 2026-09-05
View profile Send enquiry

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Frequently Asked Questions

What is the primary function of a thermal disconnector in an SPD?

The thermal disconnector monitors the temperature of the SPD's surge-arresting elements, such as the MOV. If these components overheat due to sustained overvoltage, repeated surges, or end-of-life failure, the disconnector opens the circuit permanently, preventing fire, smoke, or damage to surrounding equipment.

How does a thermal disconnector work?

It uses a low-melting-point solder or a thermally sensitive latch that holds electrical contacts closed under normal temperatures. When heat from the surge-arresting element exceeds a threshold, the solder melts or the latch releases, and a spring forces the contacts apart, creating a permanent open circuit.

What are typical electrical ratings for a thermal disconnector?

Typical rated voltages are 230/400 V AC and 500–1000 V DC for PV applications. Rated currents range from 16 to 63 A, and breaking capacity is 10–50 kA. Response time is ≤0.1 seconds. These are reference ranges; confirm with the manufacturer for your specific model.

Can a thermal disconnector be reset after activation?

No, it is a one-time device. Once the thermal disconnector trips, it must be replaced. The visible indicator (often a colored flag) shows that disconnection has occurred, and the SPD should be serviced or replaced.

Data basis: editorial classification, named public sources where available, and source-reviewed manufacturer records. See the editorial policy.

Related equipment

Applied To / Applications

This component is essential for the following industrial systems and equipment:

Surge Protection Device (SPD)
View system integration details
Surge Protection Device
View system integration details

Industrial Ecosystem & Supply Chain Structure

Industry Taxonomies & Aliases

Commonly used trade names and technical identifiers for Thermal Disconnector.

Thermal Cutoff Thermal Fuse SPD Disconnect

Data Basis

Editorial classification, named public sources where available, and source-reviewed manufacturer records.

Preliminary Technical Classification
This page supports structured research, RFQ preparation, and supplier evaluation. It does not replace buyer-led supplier qualification, standards review, or technical approval.

Compiled and source-reviewed by the CNFX editorial team. Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review · Page last updated 13 October 2026

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