What Is Ex q Powder Filling Protection? Complete Guide to IEC 60079-5
Electrical equipment used in hazardous areas must be designed to prevent ignition of explosive atmospheres. Common protection concepts include Ex d flameproof protection, Ex e increased safety, Ex i intrinsic safety, and Ex m encapsulation. Another specialized method is Ex q, which uses powder filling to prevent an internal ignition event from igniting the surrounding atmosphere.
IEC 60079-5 specifies the construction, testing, and marking requirements for equipment protected by powder filling. The method relies on filling the relevant enclosure with a specified material that restricts flame propagation and prevents an internal ignition from igniting the external explosive atmosphere.
Ex q is less common than several other protection concepts, but it remains relevant for certain electrical components and assemblies, including equipment containing transformers, relays, fuses, and electronic circuits.
What Is Ex q Powder Filling Protection?
Ex q is a type of explosion protection in which electrical components capable of igniting an explosive gas atmosphere are fixed in position and completely surrounded by a specified filling material.
Under IEC 60079-5, the filling material consists of solid quartz or solid glass particles. The material fills the available space around the protected components and creates a structure that restricts the propagation of flame through the filling.
An explosive gas atmosphere may still penetrate the equipment and, in some circumstances, be ignited by an internal circuit. The protection principle is that the small free volumes and flame-quenching paths within the filling prevent that ignition from propagating to the external atmosphere.
Therefore, Ex q should not be described simply as a method that prevents all gas from entering the enclosure. Its protective function depends on the specified filling material, construction, clearances, and certified design.
How Does Ex q Protection Work?
Ex q equipment is constructed with an enclosure or container that holds the electrical components and filling material. The relevant internal spaces are filled so that the protected components are surrounded by the specified particles.
The protection relies on several design features:
- Controlled filling material: solid quartz or glass particles with a specified size range are used.
- Complete filling: the filling procedure must avoid unfilled voids that could undermine the protection principle.
- Flame quenching: the small spaces and paths through the filling restrict flame propagation.
- Secure enclosure: the container must retain the filling material and comply with applicable construction requirements.
- Temperature control: the equipment must meet the applicable temperature limitations during normal operation and specified malfunction conditions.
These features work together as part of a certified design. Simply filling an electrical enclosure with quartz or glass particles does not make the equipment Ex q compliant.
What Filling Material Is Used in Ex q Equipment?
IEC 60079-5 specifies solid quartz or solid glass particles as the filling material. The material specification and particle size range must be documented by the manufacturer.
The standard includes particle-size requirements based on specified sieve apertures. It also addresses the filling process and measures intended to ensure that the material is properly distributed around the components.
Not every powder or mineral material is suitable. Material selection must follow the applicable standard and the equipment manufacturer's certified design.
IEC 60079-5 Requirements for Ex q Equipment
IEC 60079-5 supplements the general equipment requirements of IEC 60079-0. The consolidated edition IEC 60079-5:2015+A1:2022 specifies requirements for the construction, testing, and marking of equipment, parts of equipment, and Ex components using powder filling protection.
Important areas addressed by the standard include:
- Enclosure construction, closure, and sealing
- Pressure testing of the filling container
- Ingress protection requirements
- Filling material specifications and documentation
- Filling procedures and distances through the material
- Electrical connections and component arrangements
- Protection against excessive temperatures
- Testing and marking of the completed equipment
The standard's scope includes equipment with rated supply current not exceeding 16 A, rated supply voltage not exceeding 1,000 V, and rated power consumption not exceeding 1,000 W. Confirm the scope and detailed conditions in the applicable standard before determining whether a particular design can use Ex q protection.
Equipment must be evaluated as a complete certified design. Compliance cannot be established by checking the filling material alone.
Equipment Protection Level for Ex q
IEC 60079-5 associates powder filling protection with EPL Gb or Mb. It does not define a general Ex qc protection level under the 2015+A1:2022 edition.
| EPL | Atmosphere | Typical application |
|---|---|---|
| Gb | Gas | Generally suitable for Zone 1 and Zone 2 |
| Mb | Combustible dust in mines susceptible to firedamp | Mining applications where the applicable certification permits |
EPL Gb indicates a high level of protection for gas atmospheres and is generally suitable for Zone 1 and Zone 2. EPL Mb applies to the relevant mining environment. These designations are not interchangeable; the complete equipment marking and certificate determine the permitted application.
Do not assume that Ex q is suitable for Zone 0. Where Zone 0 requires EPL Ga, the equipment must have protection and certification appropriate to that level.
Where Is Ex q Used?
Powder filling can be applied to certain electrical equipment and Ex components whose internal construction is suitable for this method. Examples identified in the IEC 60079-5 scope include:
- Electronic circuits
- Transformers
- Protection fuses
- Relays and switches
- Intrinsically safe electrical apparatus
- Associated electrical apparatus
These examples do not mean that every transformer, relay, or electronic assembly can be certified as Ex q. Suitability depends on the electrical ratings, internal construction, filling arrangement, temperature limits, and other applicable requirements.
Ex q can also be used as one protection method within a larger equipment assembly, provided the complete assembly satisfies the applicable certification requirements.
How to Read an Ex q Equipment Marking
Consider this illustrative gas-atmosphere marking:
Ex q IIB T4 Gb
This example illustrates the principal marking elements:
- Ex: equipment intended for use in explosive atmospheres.
- q: powder filling protection.
- IIB: gas subgroup for which the equipment is certified.
- T4: temperature class, corresponding to a maximum surface temperature of 135°C under the applicable specified conditions.
- Gb: Equipment Protection Level for gas atmospheres.
This is an illustrative format, not a substitute for an actual certificate or nameplate. The complete marking must be checked against the applicable standard edition and certification documents.
For additional guidance, see How to Read IECEx Equipment Markings and Equipment Protection Level (EPL) Explained.
Ex q vs Ex m: What Is the Difference?
Ex q and Ex m use different materials and construction methods to prevent ignition of the surrounding explosive atmosphere.
| Feature | Ex q | Ex m |
|---|---|---|
| Protection method | Powder filling | Encapsulation |
| Protective material | Solid quartz or glass particles | Encapsulating compound |
| Construction | Components surrounded by filling material inside a container | Components protected by an encapsulating compound |
| Relevant standard | IEC 60079-5 | IEC 60079-18 |
Neither method is universally better than the other. Selection depends on the equipment design, required protection level, certification, and operating conditions.
Read also What Is Ex m Encapsulation Protection?.
Inspection, Maintenance, and Replacement Considerations
Powder filling is part of the equipment's certified protection system. Opening the enclosure, losing filling material, changing components, or altering the filling arrangement can affect its protective function.
When inspecting or maintaining Ex q equipment:
- Verify the complete equipment marking and certificate.
- Check for damage to the enclosure, seals, or filling container.
- Look for evidence of unauthorised opening or modification.
- Follow the manufacturer's instructions for repair, refilling, and resealing.
- Confirm that any replacement components preserve the certified design.
- Do not substitute filling material without explicit manufacturer approval and compliance with certification requirements.
Some Ex q containers are permanently sealed, while others are designed to be opened for repair under specified conditions. Maintenance personnel must follow the arrangement and restrictions stated in the certificate and manufacturer documentation.
Frequently Asked Questions
What does Ex q stand for?
Ex q identifies powder filling protection. Electrical components are surrounded by specified filling material to prevent an internal ignition from igniting the external explosive gas atmosphere.
Which standard covers Ex q protection?
IEC 60079-5 covers equipment protection by powder filling “q”. IEC 60079-0 provides general requirements for equipment used in explosive atmospheres.
What material is used in Ex q equipment?
IEC 60079-5 specifies solid quartz or solid glass particles. The material and particle size must comply with the requirements for the certified design.
Does Ex q provide EPL Gb or Gc?
IEC 60079-5:2015+A1:2022 associates powder filling protection with EPL Gb or Mb. Do not assume that Ex qc/Gc is defined by this edition; verify the exact marking and applicable certificate.
Can Ex q equipment be used in Zone 0?
Ex q is associated with EPL Gb or Mb, not EPL Ga. It should not be selected for a Zone 0 gas application requiring EPL Ga.
Is every quartz-filled electrical enclosure Ex q?
No. The equipment must meet the construction, filling, testing, marking, and certification requirements of IEC 60079-5. The presence of quartz or glass particles alone does not establish compliance.
Conclusion
Ex q powder filling is a specialized explosion protection method defined in IEC 60079-5. It surrounds ignition-capable components with specified solid quartz or glass particles to prevent an internal ignition event from igniting the surrounding explosive gas atmosphere.
The standard associates this protection method with EPL Gb or Mb. Correct selection therefore requires verification of the hazardous area, equipment marking, electrical ratings, filling design, temperature limits, and certification.
For engineers, inspectors, and procurement teams, the key is to evaluate the complete certified equipment rather than relying on the protection designation or filling material alone.
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