1. Principle of Flameproof Type (Ex d): 

The shell of the flameproof explosion-proof control box can withstand the explosion pressure generated by the explosion of the internal explosive mixture and can prevent the explosion flame from spreading to the explosive mixture around the shell. The flameproof joint surface between the components of the shell has sufficient parameters such as clearance, length, and surface roughness, so that the high-temperature and high-pressure flame generated by the explosion is rapidly cooled and extinguished when passing through the flameproof gap, so as to achieve the purpose of isolating the explosion.

2. Principle of Increased Safety Type (Ex e): 

The increased safety explosion-proof control box is based on the equipment structure that does not generate electric arcs, sparks, or high temperatures that may ignite the explosive mixture under normal operating conditions, and measures are taken to improve the safety level to avoid the occurrence of these phenomena under normal and approved overload conditions. For example, increasing the electrical clearance and creepage distance, strengthening insulation, using high-quality materials, etc., to reduce the possibility of generating sparks, arcs, and dangerous high temperatures.

3. Principle of Intrinsically Safe Type (Ex i): 

The intrinsically safe explosion-proof control box limits the energy in the circuit so that the electric sparks and thermal effects generated by the circuit under normal working and specified fault conditions cannot ignite the specified explosive mixture. The voltage and current in the circuit are limited within a small range. Even in the event of faults such as short circuits and open circuits, the released energy is not enough to ignite the surrounding explosive environment.

4. Principle of Pressurization Type (Ex p): 

The pressurization explosion-proof control box passes protective gas (such as clean air, inert gas, etc.) into the box to keep a certain pressure in the box and prevent the external explosive mixture from entering the box. And the internal electrical components are installed under the specified positive pressure conditions to ensure that no ignition sources such as sparks and arcs are generated during operation.

5. Principle of Oil-filled Type (Ex o): 

The charged components that may generate sparks, arcs, or dangerous temperatures are immersed in insulating oil so that it cannot ignite the explosive mixture above the oil surface.

6. Principle of Sand-filled Type (Ex q): 

Fill the shell with sand grains or powder materials with other specified characteristics so that under the specified operating conditions, the arc generated in the shell, the propagated flame, and the overheating temperature of the shell wall or the surface of the sand material cannot ignite the surrounding explosive mixture.