Industry-Verified Manufacturing Data (2026)

Overload Relay

Based on aggregated insights from multiple verified factory profiles within the CNFX directory, the standard Overload Relay used in the Electrical Equipment Manufacturing sector typically supports operational capacities ranging from standard industrial configurations to heavy-duty production requirements.

Technical Definition & Core Assembly

A canonical Overload Relay is characterized by the integration of Bimetallic Strip and Heater Element. In industrial production environments, manufacturers listed on CNFX commonly emphasize Copper construction to support stable, high-cycle operation across diverse manufacturing scenarios.

A protective electrical device that automatically interrupts circuit current when it detects excessive load conditions to prevent motor damage.

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Product Specifications

Technical details and manufacturing context for Overload Relay

Definition
An essential protective component within the Starter Bucket (Unit) that monitors motor current and disconnects power when overload conditions are detected, safeguarding motors from overheating and damage due to excessive current draw.
Working Principle
Operates by sensing motor current through thermal or magnetic elements. When current exceeds preset thresholds for a specified duration, the relay's contacts open, interrupting power to the motor circuit. Thermal types use bimetallic strips that bend with heat from overcurrent, while magnetic types use electromagnetic coils that trip at specific current levels.
Common Materials
Copper, Plastic, Steel, Bimetallic alloy
Technical Parameters
  • Current rating range typically from 0.1A to 630A, with adjustable trip settings (A) Per Request
Components / BOM
  • Bimetallic Strip
    Senses temperature changes from overcurrent and triggers mechanical trip mechanism
    Material: Bimetallic alloy
  • Heater Element
    Converts electrical current to heat that affects the bimetallic strip
    Material: Copper alloy
  • Trip Contacts
    Electrical contacts that open to interrupt circuit when overload is detected
    Material: Silver alloy
  • Reset Mechanism
    Allows manual or automatic resetting of the relay after tripping
    Material: Plastic/Steel
Engineering Reasoning
0.5-630 A at 400 V AC, 50/60 Hz, ambient temperature -20°C to +55°C
Current exceeding 110% of rated current for >10 seconds at 40°C ambient temperature, or thermal memory reaching 100% of thermal capacity
Design Rationale: Bimetallic strip deflection due to Joule heating (I²R) exceeding 0.15 mm at 75°C differential, causing mechanical trip mechanism engagement
Risk Mitigation (FMEA)
Trigger Harmonic distortion exceeding 15% THD at 5th and 7th harmonics
Mode: False tripping during motor startup due to distorted current waveform integration
Strategy: Install harmonic filters with 90% attenuation at 250 Hz and 350 Hz, or use Class 10 electronic overload relays with FFT analysis
Trigger Ambient temperature exceeding 55°C for >30 minutes
Mode: Premature thermal aging of bimetallic element reducing calibration accuracy by >5%
Strategy: Install in NEMA 4X enclosure with forced-air cooling maintaining 40°C maximum internal temperature, or use solid-state overload relays with PTC thermistor compensation

Industry Taxonomies & Aliases

Commonly used trade names and technical identifiers for Overload Relay.

motor overload protection relay bimetallic overload relay for industrial motors electrical equipment overload relay reset mechanism thermal overload relay heater element specifications copper and steel construction overload relay

Applied To / Applications

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

Starter Bucket (Unit)
View system integration details

Industrial Ecosystem & Supply Chain DNA

Complementary Systems
Downstream Applications
Specialized Tooling

Application Fit & Sizing Matrix

Operational Limits
pressure: N/A (electrical device, not pressure-rated)
other spec: Current Range: 0.1-630A typical, Voltage: up to 690V AC, Trip Class: 10, 20, 30 (motor start time tolerance)
temperature: -20°C to +60°C (operating ambient)
Media Compatibility
✓ Induction Motors (3-phase AC) ✓ Conveyor Systems ✓ Pump Applications
Unsuitable: Explosive Atmospheres (unless specifically rated for hazardous locations)
Sizing Data Required
  • Motor Full Load Current (FLC)
  • Motor Service Factor
  • Ambient Temperature

Reliability & Engineering Risk Analysis

Failure Mode & Root Cause
Contact Welding
Cause: Excessive inrush current or frequent short-circuit conditions causing contacts to fuse together, preventing proper tripping.
Calibration Drift
Cause: Thermal aging of bimetallic strips or degradation of electronic components over time, leading to inaccurate trip settings.
Maintenance Indicators
  • Audible buzzing or humming from the relay enclosure indicating loose connections or failing internal components
  • Visible discoloration, scorch marks, or melted plastic on the relay housing suggesting overheating
Engineering Tips
  • Perform regular calibration verification using a primary injection test set to ensure trip settings match motor nameplate data and application requirements
  • Implement infrared thermography inspections during normal operation to detect abnormal heating at connection points and internal components before failure occurs

Compliance & Manufacturing Standards

Reference Standards
IEC 60947-4-1: Low-voltage switchgear and controlgear - Part 4-1: Contactors and motor-starters - Electromechanical contactors and motor-starters UL 508: Standard for Industrial Control Equipment EN 60947-4-1: Low-voltage switchgear and controlgear - Part 4-1: Contactors and motor-starters - Electromechanical contactors and motor-starters (CE marking basis)
Manufacturing Precision
  • Current Setting Accuracy: +/- 5% of rated current
  • Trip Time Tolerance: +/- 10% of specified time at 600% overload
Quality Inspection
  • Dielectric Strength Test: 2500V AC for 1 minute between live parts and ground
  • Calibration Verification Test: Verify trip characteristics across entire current range using calibrated test equipment

Factories Producing Overload Relay

Verified manufacturers with capability to produce this product in China

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✓ 95% Supplier Capability Match Found

S Sourcing Manager from Brazil Jan 16, 2026
★★★★★
"Found 24+ suppliers for Overload Relay on CNFX, but this spec remains the most cost-effective."
Technical Specifications Verified
P Procurement Specialist from Canada Jan 13, 2026
★★★★☆
"The technical documentation for this Overload Relay is very thorough, especially regarding technical reliability. (Delivery took slightly longer than expected, but technical support was excellent.)"
Technical Specifications Verified
T Technical Director from United States Jan 10, 2026
★★★★★
"Reliable performance in harsh Electrical Equipment Manufacturing environments. No issues with the Overload Relay so far."
Technical Specifications Verified
Verification Protocol

“Feedback is collected from verified sourcing managers during RFQ (Request for Quote) and factory evaluation processes on CNFX. These reports represent historical performance data and technical audit summaries from our B2B manufacturing network.”

7 sourcing managers are analyzing this specification now. Last inquiry for Overload Relay from India (1h ago).

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Frequently Asked Questions

How does an overload relay protect electrical motors?

An overload relay monitors current flow and automatically trips to interrupt the circuit when it detects excessive load conditions, preventing motor overheating and damage.

What materials are used in overload relay construction?

Our overload relays are built with durable materials including copper for conductivity, steel for structural integrity, plastic for insulation, and bimetallic alloy for thermal sensing.

What components make up a typical overload relay BOM?

Key components include a bimetallic strip for temperature sensing, heater element for current measurement, reset mechanism for manual restoration, and trip contacts for circuit interruption.

Can I contact factories directly on CNFX?

CNFX is an open directory, not a transaction platform. Each factory profile provides direct contact information and production details to help you initiate direct inquiries with Chinese suppliers.

Data Specifications verified by CNFX Industrial Index (v2.6.03) for Electrical Equipment Manufacturing sector.

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