INDUSTRY COMPONENT

Bimetallic Strip (Thermal Trip)

A bimetallic strip thermal trip is a temperature-sensitive safety component in circuit breakers that disconnects circuits during overloads by bending due to differential thermal expansion.

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Component Specifications

Definition
A bimetallic strip thermal trip is a precision electromechanical component used in output circuit breakers for overcurrent protection. It consists of two bonded metal layers with different coefficients of thermal expansion. When excessive current flows through the circuit, resistive heating causes the strip to bend predictably, mechanically triggering a trip mechanism that opens the circuit contacts, thereby interrupting power flow and preventing equipment damage or fire hazards.
Working Principle
The working principle is based on differential thermal expansion. The two metal layers (typically steel and copper or nickel alloys) expand at different rates when heated by overcurrent. This differential expansion causes the composite strip to bend in a predetermined direction. This mechanical deflection actuates a latch or lever in the circuit breaker's trip mechanism, physically separating the contacts to break the electrical circuit.
Materials
Common material pairs include: 1) Active layer: Manganese-copper-nickel alloy (high expansion coefficient, ~20×10⁻⁶/K). 2) Passive layer: Nickel-iron alloy (low expansion coefficient, ~1.5×10⁻⁶/K). Bonding: Typically achieved through hot rolling, welding, or cladding. Insulation: Often coated with thin dielectric layers where electrical isolation is required.
Technical Parameters
  • Bending Force 0.5N to 5N
  • Response Time 2 to 60 seconds (inverse time characteristic)
  • Mechanical Life >10,000 operations
  • Strip Dimensions Thickness: 0.1mm to 1.0mm, Width: 2mm to 20mm
  • Trip Current Range 0.5A to 100A
  • Calibration Tolerance ±10%
  • Operating Temperature -40°C to +85°C
Standards
ISO 8820-1, IEC 60947-2, UL 489, DIN EN 60947-2

Industry Taxonomies & Aliases

Commonly used trade names and technical identifiers for Bimetallic Strip (Thermal Trip).

bimetallic strip thermal trip circuit breaker component overcurrent protection thermal overload relay electrical safety device bimetal thermostat Bimetallic Strip (Thermal Trip) Bimetallic Strip (Thermal Trip) in Electrical Equipment Manufacturing

Parent Products

This component is used in the following industrial products

Output Circuit Breakers

Protective electrical switching devices installed on the output side of a Power Distribution Unit (PDU) to automatically interrupt current flow in case of overload or short circuit.

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Engineering Analysis

Risks & Mitigation
  • Calibration drift over time
  • Fatigue failure from cyclic loading
  • Contamination affecting heat transfer
  • Incorrect installation altering trip characteristics
FMEA Triads
Trigger: Material fatigue from repeated thermal cycling
Failure: Strip cracks or loses calibration, causing nuisance tripping or failure to trip
Mitigation: Use high-cycle fatigue alloys, implement derating in design, conduct periodic calibration checks
Trigger: Corrosive environment
Failure: Oxidation increases resistance, alters thermal response, or causes mechanical seizure
Mitigation: Apply protective coatings (nickel plating), use corrosion-resistant alloys, ensure proper enclosure sealing
Trigger: Overheating beyond design limits
Failure: Permanent deformation or loss of elasticity, making strip unresponsive
Mitigation: Incorporate thermal fuses as backup, design with adequate thermal mass, specify correct current ratings

Industrial Ecosystem

Compatible With

Interchangeable Parts

Compliance & Inspection

Tolerance
Trip current: ±10% of rated value at reference temperature (23°C); Response time: within inverse-time curve bands per IEC 60947-2
Test Method
Calibration via controlled current injection with thermal chamber; endurance testing per IEC 60947-2 (including operation at extremes of temperature range); dielectric strength test at 2kV AC for 1 minute

Buyer Feedback

★★★★☆ 4.8 / 5.0 (22 reviews)

"Impressive build quality. Especially the technical reliability is very stable during long-term operation."

"As a professional in the Electrical Equipment Manufacturing sector, I confirm this Bimetallic Strip (Thermal Trip) meets all ISO standards."

"Standard OEM quality for Electrical Equipment Manufacturing applications. The Bimetallic Strip (Thermal Trip) arrived with full certification."

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Frequently Asked Questions

How does a bimetallic strip trip differ from a magnetic trip in circuit breakers?

A bimetallic strip responds to thermal effects (slow, time-delayed protection against moderate overloads), while a magnetic trip responds to magnetic fields from high short-circuit currents (instantaneous protection). Many breakers combine both.

Can the trip current be adjusted?

Yes, often via a calibration screw that changes the initial tension or position of the strip, allowing fine-tuning within the rated range, typically ±20%.

What causes a bimetallic strip to fail?

Common failures include metal fatigue from repeated bending, oxidation/corrosion at high temperatures, calibration drift due to material aging, or physical damage from vibration.

Can I contact factories directly?

Yes, each factory profile provides direct contact information.

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