Intrinsically Safe Control Relays: Specifications & Application Guide

In hazardous industrial environments, safe electrical control is essential to preventing equipment failure, ignition, and worker injury. Facilities in oil & gas, chemical processing, mining, food production, grain handling, and pharmaceuticals depend on control circuits that cannot generate sparks, arcs, or excess heat. This is where an intrinsically safe control relay becomes a fundamental component of explosion prevention systems.

This guide explains what intrinsically safe control relays do, how they work in safety circuits, key technical specifications, compliance requirements, and recommended applications—supported by tables, product category references, and best-practice engineering insights.

What Is an Intrinsically Safe Control Relay?

An intrinsically safe control relay is an electrical switching device designed to operate in hazardous locations without releasing enough energy—thermal or electrical—to ignite an explosive atmosphere. Instead of simply containing an explosion (like explosion-proof equipment), intrinsic safety prevents ignition from occurring in the first place by limiting voltage, current, and stored energy.

These relays are used to safely control low-energy signals in industrial processes such as emergency shutoffs, pump control, motor operation, valve actuation, alarm circuits, and monitoring systems located in Zones 0, 1, 2, or Class I, II, and III Divisions.

How Does an Intrinsically Safe Control Relay Work?

Intrinsically safe control relays function by receiving a low-power signal from field devices inside a hazardous area and safely interfacing it with non-hazardous control equipment. They are engineered to prevent electrical faults—like short circuits or coil failures—from conducing enough power into the danger zone to trigger ignition.

They typically work in combination with intrinsically safe barriers or galvanic isolators, which restrict electrical energy to a mathematically safe threshold. The relay then switches higher-power circuits in a safe (non-hazardous) zone.

The result: The hazardous location stays protected from electrical ignition sources while still allowing normal industrial operation.

Why Are Intrinsically Safe Control Relays Important for Explosion Prevention?

Intrinsically safe control relays serve three primary safety functions that make them essential in explosion prevention systems:

They Prevent Ignition in Hazardous Zones

All energy entering the hazardous area is limited to safe levels—often by pairing the relay with an intrinsically safe barrier or isolator.

They Enable Safe Switching of Critical Circuits

Emergency stop circuits, alarms, pumps, solenoids, and instrumentation require reliable switching even in hazardous environments.

They Protect Personnel, Equipment, and Operations

In industries where a single spark can cause catastrophic explosions, intrinsically safe switching is an insurance policy against electrical ignition.

As a result, these relays are standard components in refinery control rooms, chemical batching systems, oil rigs, tank farms, grain silos, and gas detection networks.

What Are the Key Specifications of an Intrinsically Safe Control Relay?

Below is an overview of the most important specifications to consider.

Input & Output Specifications

• Input voltage: Typically 12–30V DC

• Relay coil voltage: 24V DC is standard

• Contact rating: 5A–10A at 250V AC or 30V DC

• Current limiting: Built into associated IS barrier or relay circuitry

• Signal type: Discrete control inputs (NO/NC contacts)

Safety Ratings

• ATEX Zone 0/1/2 approval

• IECEx certification

• UL 913 (Intrinsically Safe) or UL 508

• FM & CSA Class I Division 1 or 2

• Temperature class (T-rating) ensuring safe operating heat limits

Construction Requirements

• Arc-free switching

• Encapsulated or sealed electronics

• Isolation between safe and hazardous circuits

• Fail-safe design to ensure controlled shutdown

Environmental Ratings

• Wide-temperature operation (−40°C to +60°C)

• Shock/vibration resistance

• IP50–IP66 protection depending on housing

These specifications guarantee that the relay performs reliably without creating ignition risks.

What Applications Use Intrinsically Safe Control Relays?

Intrinsically safe control relays are used anywhere low-voltage control signals must pass into or out of a hazardous area.

Common Industrial Applications

• Pump control systems in oil & gas production

• Emergency shutdown circuits (ESD)

• Gas detection systems requiring safe switching

• Valve actuation in chemical or petrochemical plants

• Alarm and annunciator systems for hazardous zones

• Monitoring instrumentation such as level switches or flow switches

• Batching and mixing systems

• Mining and tunneling equipment

• Pharmaceutical production machinery

Zones & Divisions Where They Apply

• ATEX Zones 0, 1, and 2

• Class I Div 1 & Div 2 hazardous locations

• Dust-hazard areas like grain silos (Class II)

• Fuel storage and transfer stations

Anywhere flammable gas, vapor, or dust exists, intrinsically safe relays act as a protective layer between the hazardous field devices and high-energy equipment.

What Is the Role of Intrinsically Safe Control Relays in Safety Circuits?

Intrinsic safety is one of the most reliable explosion protection techniques, and intrinsically safe control relays sit at the center of hazardous-location safety circuits.

They Serve Three Safety Circuit Functions:

1. Barrier Between Hazardous & Safe Areas

The relay ensures high-energy circuits never cross into classified zones.

2. Safe Switching of Protective Devices

Relays control alarms, emergency stops, shutdown sequences, and isolation valves—all vital for hazard mitigation.

3. Fault Containment

Even if a fault occurs on the safe side (e.g., short circuit, overcurrent, or coil failure), the intrinsically safe side remains protected.

Example: Gas Detection System Circuit

A typical IS control relay ensures that a flammable gas detector safely sends an alarm signal to the control system without increasing ignition risk in the hazardous area.

Control Relays vs. Intrinsically Safe Control Relays

Feature / Function	Standard Control Relay	Intrinsically Safe Control Relay
Hazardous area use	Not safe	Certified safe for Zone 0/1/2, Div 1/2
Spark prevention	No	Yes, energy-limited
Explosion protection method	None	Intrinsic safety (IS)
Energy limitation	No	< 1.2V, < 0.1A (depending on certification)
Applications	General industrial	Hazardous industries
Pairing required	No	Often paired with IS barrier
Cost	Lower	Higher due to certifications

This comparison highlights why intrinsically safe control relays are indispensable in explosion-risk environments.

What Types of Intrinsically Safe Control Relays Are Available?

Although designs vary across manufacturers, relays generally fall into the following categories:

Mechanical IS Relays

• Use physical contacts

• Provide reliable switching

• Often paired with barriers

• Suitable for alarms, pumps, shutdown systems

Solid-State IS Relays

• No moving parts

• High switching speed

• Ideal for automation, fast-response instrumentation

Multi-channel & Modular IS Relays

• Provide multiple relay outputs in one housing

• Used in complex process control systems

Hybrid IS Relays (Relay + Barrier)

• Combine galvanic isolation and a control relay

• Simplify panel design

• Reduce wiring complexity

These options allow engineers to tailor safety circuits to process requirements.

What Standards Govern Intrinsically Safe Control Relays?

To be compliant for use in hazardous areas, IS control relays must meet global safety standards.

ATEX (Europe)

• ATEX Directive 2014/34/EU governs equipment used in explosive atmospheres.

• Certification must match the specific Zone (0, 1, or 2).

IECEx (International)

• Ensures safe operation in explosive atmospheres worldwide.

UL & FM (United States)

• UL 913: Intrinsically Safe Apparatus

• UL 508: Industrial Control Equipment

• FM Class I, II, III Div 1/2 approvals

CSA (Canada)

• Aligns with NEC/CEC hazardous location classifications.

Major Compliance Requirements

• Verified energy limitation

• Surface temperature control

• Fault condition tolerance

• Isolation protection between circuits

These certifications provide assurance that the relay cannot cause ignition regardless of the fault mode.

Installation Requirements for Intrinsically Safe Control Relays

Correct installation is essential to maintaining intrinsic safety.

Key Requirements

• Use certified IS wiring for the hazardous area side

• Install in non-hazardous or reduced-hazard zones unless relay is certified for direct mounting

• Pair with matching IS barriers (Zener or galvanic isolators)

• Bond and ground barriers properly

• Maintain segregation between IS circuits and non-IS circuits

• Follow manufacturer entity parameters (Uo, Io, Po, Co, Lo)

Common Installation Mistakes to Avoid

• Mixing IS and non-IS conductors in the same conduit

• Failing to observe maximum cable capacitance/inductance

• Installing uncertified devices in the same junction box

• Incorrect grounding of Zener barriers

Proper installation ensures continued compliance with IS standards and long-term operational safety.

Maintenance Requirements for Intrinsically Safe Relays

Although these devices require little routine maintenance, periodic inspection ensures reliability.

Maintenance Checklist

• Inspect wiring for damage or corrosion

• Verify integrity of barriers and grounding

• Check relay coil resistance

• Confirm proper switching operation

• Replace units showing heat discoloration or mechanical wear

Intrinsic safety greatly reduces maintenance compared to explosion-proof equipment because it avoids heavy housings and mechanical flame paths.

Best Intrinsically Safe Relay Options by Application

Application	Recommended Relay Type	Key Features	Certification
Gas detection	Solid-state IS relay	Fast switching, fault-tolerant	ATEX/IECEx
Pump control	Mechanical IS relay	High contact rating	UL/CSA
Emergency shutdown (ESD)	Hybrid relay with barrier	Fail-safe switching	ATEX/IECEx
Valve actuation	Modular IS relay	Multiple channels	ATEX Zone 1
Alarm circuits	Mechanical or hybrid	Reliable contact operation	FM/UL

This simplifies choosing the right IS relay for your application.

FAQs About Intrinsically Safe Control Relays

What makes a control relay intrinsically safe?

It limits electrical energy—voltage, current, and power—to levels that cannot ignite a hazardous atmosphere.

Do intrinsically safe relays require barriers?

Yes, most installations require a Zener barrier or galvanic isolator to maintain energy limits.

Can these relays be installed directly in a hazardous area?

Some relays are certified for Zone 1 or Zone 2 mounting, but most are installed in a safe area and interface with IS wiring.

Are intrinsically safe relays the same as explosion-proof equipment?

No. Explosion-proof equipment contains an internal explosion. Intrinsic safety prevents ignition altogether.

What industries commonly use IS relays?

Oil & gas, chemical processing, mining, food production, pharmaceuticals, wastewater treatment, and grain processing.

Conclusion: Choosing the Right Intrinsically Safe Control Relay

An intrinsically safe control relay is a fundamental component for safe switching in hazardous locations. These relays ensure that critical control circuits—pumps, alarms, sensors, shutdown systems—can operate without generating enough electrical energy to ignite flammable atmospheres.

By understanding specifications, installation requirements, and application needs, engineers can design safer, more reliable explosion prevention systems. Intrinsically Safe Store offers a full range of intrinsically safe relays, barriers, and hazardous-location control equipment suitable for demanding industrial environments.