Trip Contacts: Rated Insulation Voltage 690V AC

Q: What is the difference between NO and NC trip contacts in an overload relay?

NO (Normally Open) contacts close when the relay trips, typically used to activate an alarm or indicator. NC (Normally Closed) contacts open when the relay trips, used to break the control circuit and stop the motor immediately. Both provide complementary safety functions.

Q: How often should trip contacts be inspected or replaced?

Inspect contacts during routine maintenance every 6-12 months for signs of arcing, pitting, or wear. Replace if contact resistance exceeds 100 mΩ or if physical damage is observed. Lifespan depends on operational frequency and load; refer to manufacturer specifications for exact intervals.

Q: Can trip contacts be manually reset after tripping?

Yes, most overload relays feature a manual reset button or lever that resets the trip mechanism and returns contacts to their normal state after the fault is cleared and the relay cools down. Some models offer automatic reset options for specific applications.

Component Specifications

Definition

Trip contacts are the specific switching elements within an overload relay that change state (normally open or normally closed) when the relay's thermal or magnetic sensing mechanism detects an excessive current condition. These contacts are directly responsible for interrupting power to the protected circuit or signaling the fault to a control system, thereby preventing motor burnout, equipment damage, or fire hazards. They are precision-engineered for reliable operation under repeated thermal cycling and mechanical stress.

Working Principle

Trip contacts operate based on the relay's detection principle. In thermal overload relays, a bimetallic strip heats and bends due to overcurrent, mechanically actuating the trip contacts. In electronic relays, a current sensor signals a microprocessor, which energizes a solenoid or solid-state switch to change the contact state. The contacts physically separate or connect to break the control circuit or main power circuit, ensuring immediate disconnection upon fault detection.

Materials

Contact points: Silver alloy (e.g., AgCdO, AgSnO2) for high conductivity and arc resistance. Contact carriers: Thermoplastic (e.g., PA66, PBT) with UL94 V-0 rating for insulation and flame retardancy. Springs: Phosphor bronze or stainless steel for consistent mechanical force. Terminals: Brass or copper alloy with tin plating for corrosion resistance and solderability.

Technical Parameters

Parameter	Typical range	Notes & selection driver
Electrical Life	> 100,000 operations at rated load
Mechanical Life	> 10 million operations
Contact Resistance	< 50 mΩ
Dielectric Strength	2500V AC for 1 minute
Contact Configuration	1NO + 1NC or 2NO + 2NC
Rated Insulation Voltage	690V AC
Operating Temperature Range	-25°C to +55°C
Rated Thermal Current (Ith)	Up to 100A
Rated Operational Current (Ie)	0.1A to 100A
Rated Operational Voltage (Ue)	600V AC

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

Standards

IEC 60947-4-1, UL 508, ISO 13849-1

Parent Products

This component is used in the following industrial products

Overload Relay

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

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Engineering Analysis

Risks & Mitigation

Contact welding due to high inrush currents
Insulation failure from moisture or contamination
Mechanical fatigue leading to unreliable operation
Incorrect contact rating causing overheating

FMEA Triads

Trigger: Excessive arcing during contact opening/closing
Failure: Contact welding, preventing circuit interruption
Mitigation: Use arc suppression circuits (e.g., RC snubbers), select appropriate contact material (AgSnO2), ensure proper contact pressure and alignment

Trigger: Environmental contamination (dust, oil, humidity)
Failure: Increased contact resistance, insulation breakdown
Mitigation: Apply protective enclosures (IP rating), use sealed relay designs, implement regular cleaning schedules

Trigger: Mechanical wear from frequent operation
Failure: Contact misalignment, spring fatigue, failure to trip
Mitigation: Design for rated mechanical life, use durable spring materials, conduct periodic functional testing

Industrial Ecosystem

Compatible With

Typical Suppliers & Equivalents

Compliance & Inspection

Tolerance

Contact gap: ±0.2mm; Contact force: ±10% of nominal; Operating time: ±20% of specified trip curve

Test Method

Dielectric testing per IEC 60947-1; Contact resistance measurement via 4-wire method; Mechanical endurance testing per IEC 60947-4-1; Thermal calibration using primary current injection

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

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Inspection readiness

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Supplier transparency

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Manufacturers of Trip Contacts

Manufacturer profiles associated with Trip Contacts.

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Frequently Asked Questions

What is the difference between NO and NC trip contacts in an overload relay?