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In a hazardous industrial area, the enclosure is part of the automation system’s protection strategy. The choice affects the PLC, field wiring, heat load, cable entries, maintenance access, and the documents needed for approval.
A standard cabinet may protect equipment from dust, water, corrosion, or impact. It does not, by itself, show that the equipment is suitable for an explosive atmosphere. That decision depends on the area classification, protection concept, components, installation method, and project requirements.
For engineers, EPC contractors, and OEMs, the practical task is to match those safety requirements with the actual automation design. Start with the hazardous area and the equipment list, then work toward the enclosure configuration.
Why Standard PLC Enclosures Cannot Be Used in Hazardous Areas
Explosion Risks in Industrial Automation Systems
A conventional control enclosure is usually selected for environmental protection and mechanical fit. In a hazardous area, the electrical equipment may also contain ignition sources such as switching contacts, power supplies, communications modules, or hot components.
Automation equipment may contain potential ignition sources, including:
- Electrical connections
- Switching components
- Power supply units
- Communication modules
- Heat-generating components
A spark, hot surface, or component fault can become an ignition source when flammable gas, vapor, or combustible dust is present. The enclosure and the equipment inside it therefore need a protection method that matches the classified location.
The enclosure cannot be evaluated on its own. Components, wiring, cable entries, grounding, and installation conditions all affect the final arrangement.
The enclosure must work together with the complete electrical system design, including component selection, wiring arrangement, cable entries, grounding, and installation conditions.
Difference Between Industrial Enclosures and Explosion Proof Enclosures
A common selection error is to treat IP, NEMA, and explosion protection as interchangeable. They address different risks.
Although these protection levels may appear similar, they solve different engineering problems.
| Protection Requirement | Main Purpose |
| IP Rating | Protects against water and solid particle ingress |
| NEMA Rating | Defines enclosure protection against environmental conditions |
| Explosion Protection | Controls ignition risks in hazardous locations |
A high IP rating can limit the entry of dust or water, but it does not prove suitability for a hazardous location. Ex marking, certificate scope, and installation conditions still need to be checked.
Explosion proof enclosure selection requires additional evaluation, including:
- Hazardous area classification
- Gas or dust characteristics
- Explosion protection method
- Temperature requirements
- Installation environment
- Applicable certification requirements
For this reason, hazardous-area automation projects require engineering-based selection rather than simply selecting a cabinet based on dimensions or appearance.
How to Select the Right Explosion Protection Concept for PLC Systems
Begin with the area in which the PLC enclosure will operate. The surrounding atmosphere, equipment function, maintenance method, and project approval route should be understood before anyone fixes the material or external dimensions.
Choosing a cabinet first and checking compliance later often leads to redesign. The protection method should follow the area classification and the equipment arrangement, not the other way around.
Start With Hazardous Area Classification Before Selecting an Enclosure
Hazardous-area classification describes how often an explosive atmosphere may be present in a defined location. It is the starting point for selecting equipment and wiring methods.
The classification process normally considers:
- Type of hazardous substance
- Frequency of explosive atmosphere occurrence
- Operating environment
- Installation location
- Applicable regulatory requirements
For PLC control systems, the classification affects every major design decision, including:
- Enclosure protection concept
- Component selection
- Cable gland requirements
- Internal wiring design
- Temperature limitations
Understand Zone Classification: Zone 0, Zone 1, and Zone 2
For flammable gases and vapors, IEC-based projects commonly use Zone 0, Zone 1, and Zone 2. The applicable zone must come from the project classification documents; it should not be guessed from the industry name alone.
| Zone | Description | Typical Consideration |
| Zone 0 | Explosive atmosphere exists continuously or for long periods | Requires the highest level of protection |
| Zone 1 | Explosive atmosphere is likely during normal operation | Common for process equipment areas |
| Zone 2 | Explosive atmosphere is unlikely during normal operation and exists only briefly | Requires suitable protection for occasional exposure |
Therefore, hazardous area classification should always be confirmed before selecting an explosion proof enclosure.
Consider Gas and Dust Hazard Classification
Hazardous environments are not limited to flammable gases. Many industrial facilities also involve combustible dust risks.
Typical hazardous substances include:
- Flammable gases
- Solvents and vapors
- Combustible dust
- Fine industrial particles
Gas, vapor, and combustible-dust hazards can lead to different equipment requirements. Confirm the substance, the classification method, and the relevant authority before selecting the enclosure.
Choose the Appropriate Explosion Protection Concept
Protection concepts solve different problems. The right choice depends on the equipment, the location, the available installation method, maintenance needs, and the governing project standard.
The selection should consider the equipment type, installation location, maintenance requirements, and project standards.
Common protection concepts include:
| Protection Concept | Main Principle | Typical Application |
| Ex d (Flameproof) | Contains internal explosions and prevents ignition transmission | Electrical equipment in hazardous areas |
| Ex e (Increased Safety) | Prevents sparks and excessive temperatures during normal operation | Terminal boxes and connection equipment |
| Ex p (Pressurized) | Uses protective gas or air pressure to prevent hazardous atmosphere entry | Larger control systems |
The correct protection concept depends on the complete equipment design rather than the enclosure alone.
Ex d Protection for Explosion Proof Control Enclosures
Ex d, or flameproof protection, uses an enclosure designed for the relevant protection requirements. It is not a generic label for every sealed metal cabinet, and the exact marking and certificate conditions must be checked for the selected model.
When selecting an Ex d enclosure, engineers should consider:
- Enclosure construction
- Flame path design
- Material strength
- Cable entry system
- Temperature class
Ex d protection is commonly used where flameproof protection is required for electrical equipment installed in hazardous areas.
Ex e Protection for Terminal and Connection Applications
Ex e, or increased safety, uses additional design measures to reduce the chance of arcs, sparks, or excessive temperatures during the specified operating conditions. It is not a substitute for checking the actual component and assembly requirements.
It is often considered for applications involving:
- Terminal connections
- Junction points
- Wiring interfaces
In PLC and sensor systems, terminal layout and cable management matter because field wiring is often changed during commissioning and maintenance. The arrangement should support the required separation, entry method, and access rules.
For hazardous-area wiring connections, see the HLBH02 S Series Explosion-Proof Terminal Box. The final model and certificate scope still need to match the project.
Separate Explosion Protection From IP/NEMA Protection
A hazardous-area enclosure normally has two separate questions to answer: how it limits environmental ingress, and how it prevents the equipment from becoming an ignition source.
A complete enclosure evaluation should consider both:
Environmental Protection
Including:
- Water resistance
- Dust protection
- Corrosion resistance
- Mechanical protection
Explosion Protection
Including:
- Hazardous area suitability
- Protection concept
- Certification requirements
- Temperature limitations
The final selection has to address both questions. A strong environmental rating does not compensate for missing Ex evidence, and an Ex certificate does not automatically cover every installation condition.
Example: Selecting an Explosion Proof Enclosure Solution
For a project that combines a PLC, sensors, and field terminals, the review usually follows this order:
- Confirm hazardous area classification
- Identify gas or dust hazards
- Select suitable explosion protection concept
- Define internal component requirements
- Review cable entry and wiring requirements
- Confirm required technical documents
Engineering Considerations for PLC and Sensor Integration in Hazardous Area Enclosures
PLC and sensor integration adds another layer to the enclosure decision. The assembly has to accommodate the required components and interfaces without losing sight of protection, heat, wiring, access, and documentation.
Problems usually appear when the enclosure is reviewed separately from the automation design. The review should bring together:
- Explosion protection requirements
- PLC heat generation
- Sensor wiring and signal management
- Cable entry design
- Internal component arrangement
- Maintenance accessibility
For an OEM or EPC project, these details affect installation work, commissioning, maintenance, and later changes. A supplier should be able to explain which parts of the design are confirmed and which still need project review.
PLC Power Consumption and Heat Management
PLC systems can generate meaningful internal heat when the enclosure contains controllers, power supplies, communications modules, signal converters, and terminal hardware.
- PLC controllers
- Power supply units
- Communication modules
- Signal converters
- Terminal blocks
- Other control components
In a hazardous area, temperature is part of the protection review. The component load, ambient temperature, spacing, and selected protection concept should be assessed together.
During enclosure selection, engineers should evaluate:
- Total power consumption
- Internal heat generation
- Ambient temperature
- Component spacing
- Heat dissipation requirements
Physical space alone is not enough. An enclosure can fit the components and still require a different configuration if the internal temperature or component conditions exceed the permitted limits.
For this reason, PLC enclosure design should consider the complete component layout instead of only the external enclosure dimensions.
A sensor-heavy automation system may include temperature, pressure, flow, position, and process-monitoring devices. Each connection adds to the signal, terminal, cable-entry, and maintenance requirements.
Modern industrial automation systems often require multiple sensor connections, including:
- Temperature sensors
- Pressure sensors
- Flow sensors
- Position sensors
- Process monitoring devices
These signals must be properly managed inside hazardous-area equipment.
Important design considerations include:
- Number of sensor inputs
- Signal type requirements
- Terminal arrangement
- Signal separation
- Communication interfaces
A process-monitoring PLC enclosure will normally need a different internal arrangement from a small junction box. Confirm the sensor interfaces before the enclosure drawing is finalized.
Engineers should confirm the required sensor interfaces before finalizing enclosure specifications.
A supplier should understand not only the enclosure structure but also how the electrical interfaces affect the overall design.
Cable Entry and Terminal Arrangement
Cable entry is one of the areas where a small design decision can create a large installation problem. Entry positions, gland selection, spare entries, and terminal layout should be agreed before fabrication.
The selection of cable glands, entry positions, and terminal layouts can affect:
- Installation efficiency
- Equipment sealing
- Maintenance accessibility
- Wiring organization
During project evaluation, engineers should define:
- Cable quantity
- Cable diameter range
- Entry direction
- Cable gland requirements
- Spare cable entries
- Internal terminal arrangement
If the entry plan is incomplete, installation can become slow and awkward, especially when several sensor and control cables approach the enclosure from different directions.
For applications requiring multiple field connections, terminal boxes can help organize wiring interfaces and simplify maintenance.
For related field-wiring guidance, see the Explosion-Proof Control Panel guide.
Grounding and Internal Segregation
Grounding and internal segregation should be reviewed alongside the component layout. Power, signal, and communication circuits may need different routing or separation, depending on the design and applicable requirements.
A well-designed enclosure should consider:
- Protective grounding
- Signal separation
- Power and communication wiring arrangement
- Internal component accessibility
Separating different circuits helps reduce potential interference and improves system reliability.
For automation equipment, engineers should review:
- Power wiring routes
- Low-voltage signal paths
- Communication cables
- Terminal block organization
The internal layout should support both safe operation and future maintenance.
Custom Enclosure Design Requirements for Automation Projects
Many automation projects need more than a standard enclosure size. The changes may involve dimensions, cable entries, mounting plates, terminals, windows, operators, or the way components are arranged.
Customization may involve:
- Enclosure dimensions
- Cable entry configuration
- Internal mounting plate design
- Terminal arrangement
- Component installation requirements
Every change should be checked against the applicable certificate and design conditions. A component or enclosure certificate does not automatically approve any assembly made from that component.
The final status depends on the selected components, the assembly design, the installation conditions, and the approval scope that applies to the project.
The final solution depends on:
- Selected components
- Assembly design
- Installation conditions
- Required approval scope
For a product example, review the HLE03 Series Explosion-Proof Enclosures. Treat the certificate and configuration as model-specific.
For background material, use Hexlon’s Explosion Protection Knowledge resource.
Example: Designing an Explosion Proof Enclosure for an Automated Production Line
Take an automated production line as an example. Its hazardous-area cell may contain a PLC, remote I/O, sensors, communications equipment, and power distribution in different locations.
The system may include:
- PLC controller
- Remote I/O modules
- Multiple sensors
- Communication interfaces
- Power distribution components
Before selecting an enclosure, the engineering team should review:
- Hazardous area classification
- Required explosion protection concept
- Internal component arrangement
- Heat generation
- Cable entry requirements
- Required documentation
The goal is a configuration that fits the automation system and the classified-area requirements, with the assumptions visible before the quotation is accepted.
Key Questions to Review Before Selecting a Supplier
Before requesting a quotation, engineers should prepare the following information:
| Requirement | Information to Provide |
| Hazardous area | Zone classification and environment |
| Automation components | PLC, sensors, communication modules |
| Electrical requirements | Voltage, power consumption, interfaces |
| Mechanical requirements | Dimensions and installation conditions |
| Cable requirements | Quantity, size, entry locations |
| Documentation | Required certificates and technical documents |
Providing this information early helps suppliers evaluate the project more accurately and avoid design changes later.
How to Prepare an RFQ for a Hazardous Area PLC Enclosure Project
A quotation request for a hazardous-area PLC enclosure should contain more than an external size. Suppliers need enough information to review the environment, component load, interfaces, cable entries, and required documents.
A clear RFQ reduces back-and-forth questions and makes supplier quotations easier to compare. It also exposes missing design information before fabrication begins.
Engineers, EPC contractors, and OEMs can improve the selection process by preparing the application data at the start of the inquiry.
Information Suppliers Need Before Quotation
Before requesting a quotation for a hazardous-area PLC enclosure project, customers should prepare the following information.
| Requirement | Information to Provide | Why It Matters |
| Hazardous Area Classification | Zone classification, gas or dust environment, applicable standards | Determines suitable explosion protection concept |
| Automation Components | PLC model, sensors, remote I/O, communication modules | Defines internal space and interface requirements |
| Electrical Requirements | Voltage, power consumption, signal type, wiring requirements | Helps evaluate internal layout and heat generation |
| Mechanical Requirements | Enclosure dimensions, installation method, mounting requirements | Determines enclosure configuration |
| Cable Entry Requirements | Cable quantity, cable diameter, entry position, gland requirements | Ensures proper sealing and installation planning |
| Documentation Requirements | Certificates, drawings, datasheets, inspection documents | Defines approval and review requirements |
Providing this information allows suppliers to evaluate not only the enclosure itself but also how the enclosure will support the complete automation application.
Define the Hazardous Environment Before Selecting Products
One of the most important steps in an RFQ is clearly describing the operating environment.
Customers should provide:
- Hazardous area classification
- Type of hazardous substance
- Ambient temperature range
- Outdoor or indoor installation conditions
- Corrosion or chemical exposure requirements
These details help determine whether an existing configuration is suitable or whether the project needs further enclosure and assembly review.
Dimensions alone are not enough. The enclosure has to match the actual atmosphere, temperature, installation method, and protection requirements.
Provide Automation System Information
For PLC and sensor applications, enclosure selection depends heavily on the internal equipment arrangement.
Customers should provide information about:
- PLC brand and model
- Number of I/O points
- Sensor quantity
- Communication interfaces
- Power supply requirements
- Terminal requirements
A small sensor connection box and a cabinet containing PLC modules, communications hardware, and several power circuits will not have the same layout or thermal requirements.
Understanding the complete equipment configuration helps suppliers evaluate:
- Internal mounting space
- Heat generation
- Cable routing
- Terminal arrangement
- Maintenance accessibility
Review Supplier Documentation Before Project Approval
For hazardous-area applications, documentation review is an important part of supplier evaluation.
Before approval, customers should confirm whether the supplier can provide:
- Product datasheets
- Technical drawings
- Installation information
- Certificate information within the defined scope
- Supporting technical documents
A certificate applies to the conditions and scope stated in that certificate. It does not automatically cover a modified enclosure, a different component set, or the completed installation.
Therefore, engineering review should be completed before final project approval.
Choosing a supplier means checking the evidence behind the proposed configuration, not only comparing prices. Engineers and procurement teams should look for model data, drawings, certificate scope, installation information, and a clear response to project-specific questions.
Hexlon supplies explosion-proof enclosures, terminal boxes, and related hazardous-area equipment for industrial applications. The relevant model and certificate scope still need to be matched to the project before a final recommendation is made.
The Hexlon product range documented in the supplied catalogs includes explosion-proof enclosures, terminal boxes, and related hazardous-area equipment. The relevant model and certificate scope still need to be matched to the project before a final recommendation is made.
For a custom request, the useful starting point is the application data: classification, equipment list, cable schedule, power and heat information, dimensions, and required documents.
For example:
- Explosion Proof Enclosure solutions, including the HLE03 series, can be evaluated for hazardous-area enclosure applications where protection requirements and installation conditions need to be considered.
- Explosion Proof Terminal Box solutions, including HLBH products, can support applications requiring organized cable connections and field wiring management.
The final configuration should be reviewed against the area classification, equipment arrangement, installation conditions, and documentation requirements.
Frequently Asked Questions
What is the difference between an explosion proof enclosure and a standard control cabinet?
A standard control cabinet mainly protects electrical components from environmental conditions such as dust, water, and mechanical impact.
An explosion proof enclosure additionally addresses ignition risks in hazardous environments through specific protection concepts and certification requirements.
How do I choose an explosion proof PLC enclosure?
The selection process should begin with:
- Hazardous area classification
- Gas or dust environment
- Required explosion protection concept
- PLC and sensor configuration
- Cable entry requirements
- Required documentation
The enclosure should be selected based on the complete application requirements rather than size alone.
Can a certified explosion proof enclosure be used for any PLC system?
No.
An enclosure certificate applies within its defined scope and conditions. A certified enclosure does not automatically mean that every customized PLC assembly or final installation is approved.
Project-specific evaluation may be required depending on component selection and installation conditions.
What information should I provide when requesting an explosion proof enclosure quotation?
Customers should provide:
- Hazardous area classification
- PLC and sensor information
- Power requirements
- Enclosure dimensions
- Cable entry requirements
- Required certificates and documents
Providing complete information helps suppliers evaluate requirements more accurately.
Does Hexlon provide customized explosion proof enclosure solutions?
Hexlon provides explosion-proof enclosures, terminal boxes, and hazardous-area equipment for industrial applications.
For customized requirements, projects should be reviewed according to application conditions, enclosure configuration, and required documentation.
Need Help Selecting an Explosion Proof Control Enclosure?
Every hazardous-area automation project has its own constraints. A complete inquiry gives the supplier a better chance of identifying the right questions before a configuration or quotation is issued.
When contacting a supplier, customers should prepare:
- Hazardous area classification
- Gas or dust environment information
- PLC and sensor list
- Power consumption requirements
- Enclosure dimensions
- Cable entry requirements
- Required certificates and documents
This information gives the supplier a workable basis for technical review and makes the response easier to evaluate.
Request Engineering Review
Send the hazardous-area classification, equipment list, interface schedule, and document requirements for a technical review.
Our team can review:
- Application environment
- Protection requirements
- Enclosure configuration
- Documentation needs
The review can then identify a suitable enclosure direction, along with any conditions that still require confirmation.
Conclusion
Selecting an explosion-proof PLC control enclosure requires a balanced review of the hazardous area, automation functions, installation conditions, and evidence required for approval.
Start with the environment and the equipment list. Then confirm the protection concept, cable entries, component arrangement, and document scope with the supplier.
That process reduces avoidable redesign during installation and commissioning.
