1. The 3 Standard Systems Behind Explosion-Proof Distribution Boxes GB 3836 · IEC 60079 · ATEX
The 3 standard systems behind explosion-proof distribution boxes:
| System | Region | Main Content | Relationship |
|---|---|---|---|
| GB 3836 series | China | Electrical apparatus for explosive atmospheres | Identical to IEC 60079 |
| IEC 60079 series | International Electrotechnical Commission | Electrical apparatus for explosive atmospheres | Internationally accepted |
| ATEX 2014/34/EU | European Union | CE certification for explosion-proof equipment | Mandatory for EU market access |
For domestic projects, follow GB 3836; for EU export, also obtain ATEX(i.e., IEC 60079 + CE certification); for export to North America, add UL / CSA. Zhejiang Golden Unicorn can coordinate with partner certificates.
2. How to choose an explosion-proof type: Ex d / e / p / i? 4 basic types + 7 sub-types
Explosion-proof electrical equipment isExplosion-proof type(explosion-proof principle) divided into 7 types, with 4 most commonly used:
| Type | Code | Principle | Application |
|---|---|---|---|
| Flameproof | Ex d | Contains internal explosion, prevents propagation to the surrounding atmosphere | Gas environment Zone 1 / 2 mainstream |
| Increased safety | Ex e | Higher safety factor | Zone 1 / 2 light hazard area |
| Pressurized | Ex p | Maintains positive internal pressure | Large control cabinet / distribution room |
| Intrinsically safe | Ex i | Limits circuit energy | Instrument / signal circuit |
| Encapsulated type | Ex m | Components encapsulated in resin | Small components / luminaires |
| Sand-filled type | Ex q | Filled with quartz sand | Luminaires / small components |
| Oil-immersed type | Ex o | Immersed in oil | Transformers / switches |
Gas environment: 90% choose Ex d IIB T4(general purpose); dust environment: choose Ex tD(dust explosion-proof); instrument signals: choose Ex ia(intrinsically safe, the safest).
3. How to choose gas group IIA / IIB / IIC? Corresponding to different explosive gases
| Group | Representative gas | Explosiveness | Application |
|---|---|---|---|
| IIA | Propane / gasoline / methanol | Low | General chemical area |
| IIB | Ethylene / dimethyl ether / coal gas | Medium | Mainstream in petrochemical / chemical |
| IIC | Hydrogen / acetylene / carbon disulfide | High | Most hazardous environment |
Selection rule of thumb:Choose IIA over IIB, choose IIB over IIC. Type IIA is the cheapest, IIC the most expensive. The vast majority of petrochemical projects can use IIB.
4. How to select temperature class T1–T6 Corresponding maximum surface temperature of equipment
| Group | Maximum surface temperature | Suitable environment |
|---|---|---|
| T1 | 450°C | No flammable gas below 450°C |
| T2 | 300°C | General chemical |
| T3 | 200°C | General chemical / fuel depot |
| T4 | 135°C | Most common (chemical / pharma / coating) |
| T5 | 100°C | Dust environment |
| T6 | 85°C | Most demanding environments |
Selection rule of thumb:Choose T6 over T5, choose T4 over T3. The lower the T number (the lower the temperature limit), the safer it is — but the more expensive. Most projects use T4 and that is sufficient.
5. Explosion-proof distribution box selection table One table covers it all
| Application | Recommended explosion-proof marking | Reason for selection |
|---|---|---|
| General chemical workshop | Ex d IIB T4 | General-purpose, budget-friendly |
| Gas station / fuel depot | Ex d IIA T3 | Gasoline / diesel, Group IIA |
| Pharma / coating | Ex d IIB T4 | T4 prevents surface high-temperature ignition |
| Hydrogen station | Ex d IIC T6 | IIC hydrogen + T6, most demanding |
| Underground coal mine | Ex d I (mining methane) | GB 3836.2 mining-duty |
| Dust workshop (flour / coal dust) | Ex tD T4 | Dust explosion-proof, not equivalent to gas |
Explosion-proof products are manufactured in joint supply with an Ex-qualified specialist factory. Zhejiang Golden Unicorn can take onexplosion-proof distribution box orders(including Ex d / Ex e / Ex tD); the specific explosion-proof rating is subject to the scope of the partner's certificate.Ex certificate verification is available; qualification documents are supplied with the shipment..
6. Five key points for accepting an explosion-proof distribution box (must-check items at site acceptance)
- Check the Ex marking: The cabinet nameplate must carry the Ex marking + explosion protection type + gas group + temperature class — all four are required.
- Check the Ex certificate: Issued by an Ex certification body; a copy stamped with the official seal, and the certificate number can be verified on the website of the China National Quality Supervision and Inspection Center for Explosion-Protected Electrical Products.
- Check the installation method: Explosion-proof conduit / explosion-proof flexible conduit / explosion-proof cable glands must match the explosion protection type — you cannot use ordinary conduit with an explosion-proof box.
- Check grounding: An explosion-proof cabinet must have a dedicated grounding terminal, with grounding resistance ≤ 4Ω.
- Check fasteners: All bolts must be stainless steel, with spring washers complete — none may be missing.
FAQ FAQ
Does Golden Unicorn hold its own Ex certificate?
Golden Unicorn can take on explosion-proof distribution box orders, manufactured in joint supply with an Ex-qualified specialist factory. The specific explosion protection rating is subject to the scope of the partner's certificate.Ex certificate verification is available; qualification documents are supplied with the shipment..
How much more does an explosion-proof distribution box cost than a standard one?
For the same specification,Ex d IIB T4 flameproof is 100–200% more expensive(thicker enclosure + complex machining + specialized components); Ex e increased safety is 50–100% more; Ex i intrinsically safe is 30–60% more. Golden Unicorn builds explosion-proof cabinets, MOQ 1 unit, 15–25 days.
How do you read the Ex d IIB T4 marking?
Ex = explosion-proof;d = flameproof;IIB = gas group IIB;T4 = maximum surface temperature 135°C. Full marking:Ex d IIB T4 Gb.Gb is the equipment protection level (EPL); Zone 1 areas use Gb.
Can an explosion-proof distribution box be fitted with circuit breakers?
Yes, but explosion-proof circuit breakers must be used(marked with the Ex d symbol). Fitting ordinary circuit breakers inside an explosion-proof cabinet defeats the purpose of explosion protection, because sparks can escape through the operating mechanism. Golden Unicorn explosion-proof cabinetscome standard with explosion-proof components(Schneider / ABB explosion-proof series).
What explosion protection is used in dust environments?
Dust environments use Ex tD dust explosion protection(GB 12476 series), which is a different system from gas explosion protection (Ex d).Common marking: Ex tD T4. Golden Unicorn can build dust explosion-proof cabinets — we have supplied flour, coal dust, aluminum powder and feed mill workshops.
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