TN - Electromechanical and Solid State Relays - Maintenance

Summary/Issue Description

General-purpose relays are essential components in many industrial systems. Proper maintenance and handling are critical for ensuring their long-term performance and avoiding unexpected system failures. This guide will provide detailed information on common relay failures, maintenance strategies, and safety precautions, with a focus on industrial settings where reliable operation is paramount.

Root Cause

The root cause of unexpected system failures in industrial settings often stems from insufficient maintenance, improper handling, or a lack of awareness regarding common failure modes of general-purpose relays. These factors can compromise relay reliability, leading to operational disruptions and reduced system performance. 

Solution

Common Relay Failures and Their Causes

Relays can experience several common failures, often due to issues with input voltage, mechanical damage, or incorrect specifications. Key failure modes include:

Failure to Operate: Caused by insufficient input voltage, incorrect relay specifications, voltage drops, damaged coils, or faulty wiring.

Failure to Release: This can happen due to residual voltage, contact welding, insulation deterioration, or mechanical damage.

Malfunctions: Incorrect input voltage or excessive vibration can cause improper operation, such as incorrect indicator lights.

Burnout: Coils or contacts may burn out if the relay is subjected to excessive voltage or current beyond its rating.

Internal issues such as contact welding, faulty contacts (due to foreign particles or corrosion), and humming from improper voltage or external vibration can also cause relay failures. 

Relay Maintenance Approaches

Relay maintenance can be divided into two main types:

Corrective Maintenance: Performed after a failure occurs, involving inspections and repairs to address the issue. Fault Tree Analysis (FTA) is useful for identifying root causes.

Preventive Maintenance: A proactive approach that includes regular inspections to identify potential issues before a failure occurs. Timing for maintenance depends on factors like:

Wear-based failures: Contact wear and mechanical wear are predictable and tied to the number of relay operations.

Deterioration-based failures: Failures like insulation deterioration are time-dependent and affected by environmental conditions.

Determining Maintenance Timing 

Maintenance timing for relays should be based on the number of operations and time elapsed. Key considerations include:

Contact Wear: Maintenance can be scheduled based on the electrical life curve or test values if no curve is available.

Mechanical Wear: The frequency of mechanical switching, especially under harsh conditions, can affect maintenance intervals.

Coil Deterioration: Coil life is influenced by operating temperature, with a reference of 40,000 hours at 120°C for most coils.

Testing Methods for Relays 

Relays should undergo regular testing to assess their condition:

Mechanical Life Testing: This test evaluates the mechanical components under no-load conditions by observing appearance and performance.

Electrical Life Testing: Performed under load, this test monitors contact wear and coil functionality over time to ensure the relay operates reliably.

Safety Precautions

To ensure safe operation and maintenance of relays, it is important to follow these safety guidelines:

1. Electrical Safety

Disconnect power: Always ensure that the relay is disconnected from the power source before performing any maintenance.

Proper wiring: Use the correct wire gauge for connections to prevent overheating, and make sure all terminals are securely tightened to avoid loose connections.

2. Mechanical Safety

Handle with care: Avoid dropping or subjecting relays to mechanical shocks, which can damage internal components.

Secure mounting: Ensure that relays are mounted in a vibration-free environment to prevent contact misalignment and early wear.

Environmental Safety

Control temperature and humidity: Relays should be installed in environments with stable temperature and humidity levels. High humidity or extreme temperatures can cause insulation deterioration or condensation inside the relay.

Protect from corrosive gases: Relay contacts are particularly vulnerable to corrosion from gases like sulfur dioxide (SO2) or hydrogen sulfide (H2S), which can lead to poor performance or failure.

Regular preventive maintenance, including inspections and testing, should be carried out based on the operational conditions of the relay. In addition, careful attention to safety precautions during installation, operation, and maintenance will further extend the lifespan of relays and reduce the likelihood of unexpected failures.

By adopting these practices, industries can ensure that their relay systems remain operational and efficient, minimizing downtime and improving overall system reliability.

Date/Revision History

First review 03/25/2024 V1.0

2nd Review 01/13/2025

Author:

Aimee Rivera, Technical Support Engineer

References

Technical Guide for General-purpose Relays