Requirements for Clearance and Creepage Distances in Increased Safety Electrical Equipment
In increased safety explosion-proof electrical equipment, clearance and creepage distances are extremely critical parameters for ensuring explosion protection performance and safe operation. The core purpose is to prevent safety hazards such as tracking or electrical breakdown between two conductive parts through the surface of insulating materials or through air. Relevant testing is used to verify whether product performance complies with standard requirements and to identify potential defects in design and manufacturing that may affect safe operation.
I. Clearance and Creepage Distances
Clearance refers to the shortest distance in air between live conductors of different potentials, and is determined based on the RMS working voltage. Creepage distance refers to the shortest path along the surface of insulating material between live conductors of different potentials. It is determined not only by the RMS working voltage but also by the comparative tracking index (CTI) of the insulating material and the degree of surface pollution.
The clearance and creepage distances between exposed conductive parts of different potentials shall be as shown in Figure 1 (not reproduced here). For field wiring terminals, the minimum distance for protection level “eb” is 3 mm, and for protection level “ec” is 1.5 mm. Alternatively, for protection level “ec”, clearances and creepage distances other than those for field wiring terminals may comply with the values specified in Appendix H of GB/T 3836.3 or IEC 60079-7.
Clearance shall be determined based on the working voltage. If the equipment has multiple rated voltages or a voltage range, the working voltage shall be taken as the highest rated voltage. Creepage distance requirements are determined based on working voltage, tracking resistance of the insulating material, and the surface shape of the insulating material.
Unless otherwise required by GB/T 3836.3 or IEC 60079-7, the reinforced clearances and creepage distances for protection level “ec” equipment apply only between the main circuit and isolated circuits. These reinforced clearances and creepage distances do not apply to printed circuit boards on which components are mounted.
II. CTI Classification Standard for Insulating Materials
GB/T 3836.3 or IEC 60079-7 provides classifications for insulating materials based on their comparative tracking index (CTI), which shall be determined in accordance with GB/T 4207. Inorganic insulating materials, such as glass and ceramic materials, do not exhibit tracking and therefore do not require CTI determination; they are typically classified as Category I materials.
III. Conclusion
In summary, strict control over the proper design of clearance and creepage distances, together with the scientific selection of CTI ratings for insulating materials, are three interrelated and indispensable factors. The specification and testing of these parameters must strictly comply with international and national standards such as GB/T 3836.3 and IEC 60079-7, while also allowing for multi-faceted verification using industry standards such as UL Yellow Cards. This ensures that products avoid safety risks such as tracking and electrical breakdown under different operating conditions. In the context of industrial production moving towards safer and more refined operations, continuously strengthening the attention to and control of these key parameters is not only an inevitable requirement for ensuring reliable equipment operation and protecting personnel and property, but also an important pillar supporting the high-quality development of the explosion-proof electrical industry.
With over a decade of experience, he is a seasoned Explosion-Proof Electrical Engineer specializing in the design and manufacture of safety and explosion-proof products. He possesses in-depth expertise across key areas including explosion-proof systems, nuclear power lighting, marine safety, fire protection, and intelligent control systems. At Warom Technology Incorporated Company, he holds dual leadership roles as Deputy Chief Engineer for International Business and Head of the International R&D Department, where he oversees R&D initiatives and ensures the precise delivery of design documentation for international projects. Committed to advancing global industrial safety, he focuses on translating complex technologies into practical solutions, helping clients implement safer, smarter, and more reliable control systems worldwide.
Qi Lingyi