Why Should Relays Be Used with Surge Protection Devices?

Introduction

Relays play a critical role in industrial control systems by switching loads, isolating signals, and protecting sensitive equipment. However, relays themselves are vulnerable to voltage surges and transient spikes caused by inductive loads, lightning, or switching operations.
To ensure long-term reliability and system safety, relays are often used together with surge protection devices (SPDs). But why is this combination so important? This article explains how surge protection enhances relay performance and prevents costly failures.

What Causes Surges in Relay Circuits?

In industrial environments, electrical surges are common and often unavoidable. Typical causes include:

• Inductive loads such as motors, solenoids, contactors, and valves

• Relay coil de-energization, which generates high back electromotive force (EMF)

• Lightning strikes or power grid fluctuations

• Frequent switching operations in automation systems

When a relay coil is switched off, the stored energy in the inductive circuit is released instantly, creating a high-voltage spike that can damage relay contacts, PLC outputs, or electronic components.

How Surge Protection Devices Protect Relays

A surge protection device limits transient overvoltage by clamping or diverting excess energy away from sensitive components.

Key protection functions include:

✔ Protecting Relay Contacts

Voltage spikes can cause arcing and contact erosion, leading to welding or premature contact failure.
SPDs suppress these spikes, extending relay contact life and maintaining stable switching performance.

✔ Protecting Relay Coils and Control Outputs

Without surge suppression, back EMF can damage:

• PLC transistor outputs

• Control circuit boards

• Low-voltage signal modules

Surge protectors absorb or redirect excess voltage, preventing insulation breakdown and electronic damage.

✔ Reducing Electromagnetic Interference (EMI)

Surges generate electrical noise that can disturb nearby signal lines.
Using SPDs helps reduce EMI, ensuring clean signals and reliable system operation.

✔ Improving Overall System Reliability

By minimizing surge-related failures, the combination of relays and surge protection significantly reduces:

• Unexpected downtime

• Maintenance frequency

• Replacement costs

This is especially critical in systems requiring 24/7 continuous operation.

Common Types of Surge Protection Used with Relays

Depending on the application and voltage type, different surge protection solutions are used:

• Flyback diodes (DC relay coils)

• RC snubber circuits (AC coils and contacts)

• Varistors (MOVs) for AC surge suppression

• Transient Voltage Suppression (TVS) diodes

• Plug-in surge protection modules integrated into relay sockets

Many modern relay sockets integrate surge protection directly, simplifying wiring and improving safety.

What Happens If Surge Protection Is Not Used?

Without surge protection, relay systems may experience:

• ⚡ Contact arcing and welding

• 🔥 Coil insulation damage

• 🛑 PLC output failures

• 📉 Reduced relay lifespan

• ❌ Unstable system behavior

Even high-quality relays can fail prematurely if exposed to repeated surge stress.

RY-ELE Relay and Surge Protection Solutions

RY-ELE offers relay sockets and interface solutions that support integrated surge suppression, providing an added layer of protection for industrial control systems.

RY-ELE advantages include:

• Relay sockets compatible with diode, RC, or varistor modules

• Compact designs for space-saving control panels

• Reliable insulation and flame-retardant materials

• Enhanced safety for PLC and control outputs

• Long-term stable performance in harsh environments

By combining RY-ELE relays with proper surge protection, engineers can build safer and more durable automation systems.

Typical Application Scenarios

• Industrial control cabinets

• PLC input/output interfaces

• Motor and solenoid control circuits

• HVAC and pump systems

• Power distribution and automation panels

In all these applications, surge protection is essential to ensure reliable relay operation and protect upstream control devices.

Conclusion

Relays are essential switching components, but they are not immune to electrical surges.
Using surge protection devices together with relays is a proven and cost-effective way to protect contacts, coils, and control electronics from transient overvoltage.

With reliable relay solutions and surge-compatible sockets from RY-ELE, engineers can significantly enhance system stability, extend equipment lifespan, and reduce maintenance costs in industrial control applications.