Bimetallic Strip (Thermal Trip): Bending Force 0.5N to 5N

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

Parameter	Typical range	Notes & selection driver
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

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

Standards

ISO 8820-1, IEC 60947-2, UL 489, DIN EN 60947-2

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

Typical Suppliers & Equivalents

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

Procurement Evaluation Criteria

A practical evidence checklist for RFQ preparation and supplier evaluation.

Technical documentation

Request current drawings, revision history, and a signed specification sheet.

Manufacturing capability

Verify equipment lists, process limits, capacity, and representative production evidence.

Inspection readiness

Confirm test methods, calibrated equipment, sampling plans, and traceable reports.

Supplier transparency

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Manufacturers of Bimetallic Strip (Thermal Trip)

Manufacturer profiles associated with Bimetallic Strip (Thermal Trip).

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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

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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.

Data Basis

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

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.

Bimetallic Strip (Thermal Trip)