Editorial Technical Reference

Magnetic Trip Unit

This page explains how Magnetic Trip Unit 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 protective component in circuit breakers that detects and responds to short-circuit currents using electromagnetic principles.

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Product Specifications

Technical details and manufacturing context for Magnetic Trip Unit

Definition
The magnetic trip unit is a critical safety component within circuit breakers and main disconnect switches that provides instantaneous protection against short-circuit faults. It operates independently of the thermal trip mechanism and is designed to respond rapidly to high-magnitude fault currents, typically within milliseconds, to prevent equipment damage and electrical hazards. This unit is an integral part of the circuit breaker's tripping system, ensuring that when a short circuit occurs, the breaker opens quickly to isolate the fault. The magnetic trip unit is characterized by its rated current range of 16–630 A, rated insulation voltage of 690 V, and rated impulse withstand voltage of 8 kV, all per IEC 60947-2. Its short-circuit release current is adjustable between 10 and 20 times the rated current, and it trips in less than 0.1 seconds under short-circuit conditions. The unit operates within a temperature range of -40°C to 85°C and is protected against solid objects and water with an IP rating of IP20 to IP40, per IEC 60529. It can withstand relative humidity up to 95% (non-condensing) and has a mechanical endurance of 10,000 operations and electrical endurance of 5,000 operations, per IEC 60947-2. The weight varies from 0.5 to 2.5 kg depending on current rating and construction, and typical mounting dimensions for a 100 A unit are 45×60×80 mm. Materials used include copper coil, steel core, magnetic armature, and insulating materials. These specifications are reference values that must be verified for the specific model and application with the legal manufacturer or supplier. The magnetic trip unit is essential for ensuring the safety and reliability of electrical distribution systems.
Working Principle
The magnetic trip unit utilizes an electromagnetic coil that generates a magnetic field proportional to the current flowing through it. When a short-circuit occurs and current exceeds the predetermined magnetic trip setting, the magnetic field becomes strong enough to attract an armature or move a plunger, which mechanically releases the trip mechanism to open the circuit breaker contacts and interrupt the fault current. This principle ensures rapid response to high fault currents, protecting downstream equipment and preventing electrical hazards.
Common Materials
Copper coil, Steel core, Magnetic armature, Insulating materials
Technical Parameters
ParameterTypical rangeNotes & selection driver
Rated Current16–630 AContinuous current the trip unit can carryIEC 60947-2
Rated Insulation Voltage690 VMaximum voltage for insulation designIEC 60947-2
Rated Impulse Withstand Voltage8 kVWithstands lightning/overvoltage impulsesIEC 60947-2
Short-Circuit Release Current10–20 ×InMultiple of rated current for magnetic tripIEC 60947-2
Trip Time at Short-Circuit<0.1 sFast response to protect circuitIEC 60947-2
Operating Temperature Range-40–85 °CFull functionality within this rangeIEC 60947-2
Degree of ProtectionIP20–IP40Protection against solid objects and waterIEC 60529
Relative Humidity≤95 %Non-condensing conditionsIEC 60947-2
Mechanical Endurance10000 operationsNumber of mechanical operations without maintenanceIEC 60947-2
Electrical Endurance5000 operationsNumber of operations under loadIEC 60947-2
Weight0.5–2.5 kgDepends on current rating and construction
Mounting Dimensions45×60×80 mmTypical footprint for 100 A unit

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
  • Electromagnetic Coil
    Generates magnetic field proportional to current flow
    Material: Copper wire with insulation
  • Magnetic Core Part
    Concentrates and directs magnetic flux
    Material: Laminated electrical steel
  • Trip Armature Part
    Moves under magnetic force to trigger trip mechanism
    Material: Ferromagnetic steel
  • Trip Spring Part
    Provides return force and assists in trip operation
    Material: Spring steel

Applied To / Applications

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

Circuit Breaker/Main Disconnect
View system integration details

Industrial Ecosystem & Supply Chain Structure

Complementary Systems
Downstream Applications
Specialized Tooling

Application Fit & Sizing Matrix

Operational Limits
pressure: Atmospheric to 1.5 bar
other spec: Short-circuit current detection range: 1kA to 100kA
temperature: -20°C to +70°C
Media Compatibility
✓ Indoor electrical panels ✓ Dry industrial environments ✓ Clean air atmospheres
Unsuitable: High humidity or corrosive chemical environments
Sizing Data Required
  • Maximum short-circuit current (kA)
  • Rated continuous current (A)
  • System voltage (V)

Reliability & Engineering Risk Analysis

Failure Mode & Root Cause
Demagnetization
Cause: Exposure to high temperatures, mechanical shock, or strong external magnetic fields that reduce the magnetic flux density below the trip threshold.
Mechanical Binding
Cause: Accumulation of dust, corrosion, or wear in the trip mechanism's moving parts, preventing proper actuation.
Maintenance Indicators
  • Audible buzzing or humming from the unit, indicating vibration or partial engagement of the trip mechanism.
  • Visible discoloration or overheating marks on the unit's housing, suggesting excessive current or poor contact.
Engineering Tips
  • Implement regular infrared thermography scans to detect abnormal heating patterns before failure occurs.
  • Ensure proper environmental sealing and controlled operating temperatures to prevent demagnetization and corrosion.

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
IEC 60947-2: Low-voltage switchgear and controlgear - Circuit-breakers UL 489: Molded-Case Circuit Breakers, Molded-Case Switches and Circuit-Breaker Enclosures

Quoted from the published standard.

Manufacturing Precision
  • Magnetic coil resistance: +/-5% of nominal value
  • Trip time delay: +/-10% of specified setting
Quality Inspection
  • Calibration verification test against current-time curve
  • Dielectric withstand test (e.g., 2.5kV for 1 minute)

Manufacturers of Magnetic Trip Unit

Manufacturer profiles associated with Magnetic Trip Unit.

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Frequently Asked Questions

What is the function of a magnetic trip unit?

It provides instantaneous protection against short-circuit currents by using an electromagnetic coil to release the trip mechanism when current exceeds a set threshold, opening the circuit breaker contacts.

What are the typical rated current ranges?

The rated current range is 16–630 A, as per IEC 60947-2. However, exact values depend on the specific model and must be confirmed with the manufacturer.

How fast does it trip on a short circuit?

The trip time is less than 0.1 seconds, ensuring rapid interruption of fault currents to protect equipment.

What standards apply to magnetic trip units?

Key standards include IEC 60947-2 for low-voltage switchgear and controlgear, and IEC 60529 for degrees of protection. Compliance should be verified with the supplier.
Data basis: editorial classification, named public sources where available, and source-reviewed manufacturer records. See the editorial policy.

Data Basis

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

Preliminary Technical Classification
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