What Are The Explosion-proof Ratings Of Explosion-proof Distribution Boxes?

The explosion-proof rating of an explosion-proof distribution box is usually not a single label, but a combination of multiple dimensions, including explosion-proof type and temperature class, to comprehensively define the hazardous environment and safety level to which it is applicable.

I. Common Explosion-Proof Types

1. Gas Atmosphere

Flameproof Type
Mark: Ex d
Principle: The enclosure can withstand the pressure generated by the explosion of the internal explosive mixture and prevent the explosion from propagating to the surrounding area.

Application: The most commonly used type, suitable for Zone 1 and Zone 2 gas environments.

 

Increased Safety Type
Mark: Ex e
Principle: For electrical equipment that will not generate arcs or sparks under normal operating conditions, measures are taken to increase the insulation class to enhance its safety.

Application: Typically used in Zone 2, often used in combination with Ex d (i.e., the enclosure contains Ex d components, and the overall certification is Ex de).

 

Intrinsically Safe Type
Mark: Ex i (ia or ib)
Principle: The energy generated by the circuit itself is insufficient to ignite the surrounding explosive atmosphere. Typically used for instrumentation and signal control, rarely used in the main circuit of high-power distribution boxes, but can be used in control circuits within distribution boxes.

 

Pressurized Type
Mark: Ex p
Principle: By maintaining the internal protective gas pressure higher than the external pressure, external explosive atmospheres are prevented from entering the enclosure.

Applications: Suitable for large distribution boxes or applications containing numerous heat-generating components.

 

2. Dust Environments
Dust Explosion-Proof Type
Marking: Ex tD or Ex t
Principle: The enclosure has the ability to prevent dust ingress and limit surface temperature.

Applications: Suitable for flammable dust environments (e.g., Zone 21, Zone 22).

 

II. Explosion-Proof Zone Classification
Explosion-proof distribution boxes are classified according to their usage location:

Class I: Electrical equipment for underground coal mines, mainly for methane and coal dust.

Class II: Electrical equipment for other explosive gas atmospheres (factory use), excluding coal mines.

Further subdivided according to hazard level: IIA, IIB, IIC, representing different gas groups.

IIC is the highest level (e.g., hydrogen, acetylene), which can cover IIB and IIA; IIB can cover IIA.

Class III: Electrical equipment for explosive dust atmospheres, excluding coal mines.

 

III. Temperature Group

Gas Temperature Groups:

T1: 450℃

T2: 300℃

T3: 200℃

T4: 135℃

T5: 100℃

T6: 85℃ (Most stringent requirement)

Common distribution boxes are mostly T4, T5, or T6, depending on the heat generation of internal components and structural design.

 

IV. Complete Explosion-Proof Rating Examples

1. Ex d IIB T4 (Applicable to Gases): Explosion-proof type, suitable for Class IIB gas environments, maximum equipment surface temperature ≤135℃.

 

2. Ex d IIC T6 (Applicable to Gases with Higher Requirements): Explosion-proof type, suitable for Class IIC gas environments (such as hydrogen), maximum equipment surface temperature ≤85℃.

 

3. Ex d e IIB T4 / Ex tD A21 IP65 (Gas + Dust Composite): The gas is explosion-proof and increased safety composite, suitable for Class IIB gases; the dust is A21 level (Zone 21 hazardous area) explosion-proof, with a protection level of IP65.