Whether the wiring chamber of an explosion-proof electric heater requires insulating paint application depends on a comprehensive evaluation of the specific explosion-proof type, standard requirements, and actual application scenarios.
I. Core Requirements of Standard Specifications
1. GB 3836.1-2021 (General Requirements for Equipment in Explosive Atmospheres)
This standard incorporates the requirements for dust environments but does not impose mandatory regulations on the insulation varnish spraying in wiring chambers for Class II equipment (such as explosion-proof electric heaters).
For Class I equipment (underground coal mines), the inner surfaces of metal wiring chambers must be coated with arc-resistant paint (such as 1320 epoxy porcelain paint) to prevent arc-induced gas explosions. However, no specific requirements are stipulated for Class II equipment (non-coal mining environments such as chemical plants, oil and gas facilities, etc.).
2. Special Design of Flameproof (Ex d) Equipment
The mating surfaces of the flameproof enclosure must undergo phosphating treatment and be coated with anti-rust oil (such as 204-1 anti-rust oil) to ensure sealing and corrosion resistance. Although anti-rust oil possesses certain insulating properties, it is not a specialized insulating paint.
If there are exposed conductors or flashover risks inside the wiring chamber, the design must comply with standards (e.g., GB/T 16935.1) through clearance and creepage distance, rather than relying solely on insulating varnish.
3. Insulation Requirements for Increased Safety (Ex e) Equipment
Enhanced safety equipment must ensure no sparks during normal operation, with its wiring chamber's insulation performance primarily relying on insulating materials (such as ceramics, epoxy resin) and conductor sheathing, rather than surface coating of the chamber.
If the surface of the insulating component is damaged, it should be repaired with insulating paint of the same grade, but there is no requirement for the entire cavity to be coated.
II. Technical Considerations in Practical Applications
1. Functions and Limitations of Insulating Varnish
Advantages: Insulating paint can enhance surface insulation strength (such as arc resistance and leakage prevention), making it particularly suitable for high humidity or dusty environments. For example, applying 20-30μm of epoxy insulating paint can increase the insulation resistance retention rate to over 85%.
Risk: Insulating paint may affect heat dissipation. For instance, an explosion-proof electric heater optimizes heat dissipation through cooling vents and inert gas filling. Excessive spraying could disrupt thermal balance. Additionally, insulating paint must pass high-temperature resistance tests (e.g., above 150°C) or it may fail.
2. Industry Practice and Manufacturer Processes
Ex-dustproof equipment: Most manufacturers apply a rust-preventive primer (e.g., C06-1 iron red alkyd primer) inside the wiring chamber, but insulating paint is not mandatory. For instance, a certain explosion-proof motor junction box employs a "primer + arc-resistant magnetic paint" combination, reinforcing insulation only in the terminal area.
Increased safety equipment: Greater emphasis is placed on the mechanical reliability of conductor connections (such as anti-loosening terminals) and the selection of insulating materials, while cavity spraying is not necessary.
3. Additional Requirements for Special Scenarios
High-corrosion environments (such as coastal or chemical industrial areas): Apply anti-corrosion insulating paint (e.g., ZS-1091 ceramic insulating coating) to ensure both chemical resistance and insulation.
High-voltage equipment (e.g., above 10kV): Gradient-thickness anti-corona paint should be applied to suppress partial discharges.
III. Conclusion and Recommendations
1. Mandatory spraying scenarios
Only the wiring chambers of Class I equipment (for underground coal mines) are required to be mandatorily coated with arc-resistant paint.
If the equipment enhances its explosion-proof performance by applying insulating paint (e.g., to meet higher IP ratings or corrosion resistance), this must be clearly stated in the certification documents.
2. Non-mandatory but recommended scenarios
For Class II equipment, it is recommended to apply insulating paint if the following conditions exist:
The wiring chamber has a compact space, with the electrical clearance or creepage distance approaching the standard limit.
High ambient humidity (e.g., RH > 90%) or presence of conductive dust.
The equipment requires long-term operation and is difficult to maintain (e.g., buried or sealed installation).
It is recommended to select high-temperature-resistant (≥135°C) and strongly adhesive insulating paint (such as epoxy polyester paint), with a thickness controlled between 20-30μm to balance insulation and heat dissipation.
3. Process and Verification
Before spraying, the cavity must undergo sandblasting treatment (Sa2.5 grade) to ensure paint film adhesion.
After completion, the insulation resistance (≥10MΩ) and dielectric strength (e.g., 1760V/2min) must be tested, and the salt spray test (e.g., 5% NaCl solution, 1000 hours without rusting) must be passed.
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Post time: Oct-09-2025
