1. What an Explosion-Proof Control Cabinet Consists Of and Where It Is Used (enclosure + control components)
A single explosion-proof control cabinet = explosion-proof enclosure + control circuit components(circuit breakers, contactors, relays, terminals, pushbuttons, indicator lights). The application challenge: a control cabinet contains both power circuits and operator devices, and people operate it frequently — so the choice of enclosure type matters more than it does for a distribution box. Typical applications: pump control in petrochemical plants, temperature control for chemical reactors, and process interlocking in oil and gas loading areas.
2. Ex d Flameproof Control Cabinets (GB 3836.2)
Principle: The enclosure is rugged and the flameproof joint faces are precision-machined, so an internal explosion cannot escape. Control components are mounted inside the flameproof cavity, and pushbuttons are actuated through flameproof operating rods.
- Advantages: Suitable for Zone 1. The most complete protection, with few restrictions on internal components.
- Drawbacks: The housing is heavy (cast aluminum / thick steel plate), and cost rises sharply for large cabinets; heat dissipation is poor, so high-dissipation components require derating.
- Suitable forFor small to medium control boxes and pushbutton stations, and where there are many power circuits.
3. Ex e increased safety control cabinet (GB 3836.3)
Principle: It does not rely on "containing an explosion" but instead, at the source,eliminates or suppresses sparks and high temperatures— terminals have increased creepage distance, conductors have larger cross-sections, and connections are vibration-proof and loosening-proof, so no ignition source is produced under normal conditions.
- Advantages: The enclosure is light, low cost, and has good heat dissipation.
- Drawbacks: Internally,there must be no spark source— components with contact sparking such as contactors and relays cannot be installed (unless they are themselves flameproof/intrinsically safe components).
- Suitable for: Zone 2 junction boxes and terminal boxes with non-contact circuits.
4. Ex p pressurized control cabinet (GB 3836.5)
Principle: Continuously feeds clean protective gas (air or inert gas) into the cabinet, maintaining internal pressureabove the external hazardous environment, preventing combustible gas from entering; standard industrial components can be used inside the cabinet.
- Advantages: Large cabinets gain almost no additional weight, standard PLCs/VFDs can be used inside, and heat is carried out by exhaust gas.
- Drawbacks: Requires an air supply, purge interlock, and pressure-loss protection system — high O&M demands.
- Suitable for: Large control cabinets, explosion-proof VFD panels, pressurized analyzer shelters.
5. How to choose among the three types? (one table to decide)
| Dimension | Ex d flameproof | Ex e increased safety | Ex p pressurized |
|---|---|---|---|
| Applicable zone | Zone 1 / Zone 2 | Zone 2 | Zone 1 / Zone 2 (after purge) |
| Internal components | Few restrictions | No spark sources permitted | Standard components allowed |
| Cabinet size | Mainly small to medium | Small to medium | Clear advantage for large cabinets |
| Cost | Enclosure is expensive | Lowest | Complex system, O&M cost |
| Typical products | Explosion-proof control box / pushbutton box | Explosion-proof junction box | Pressurized control cabinet / explosion-proof VFD panel |
Decision sequence:Zone 2 — prefer Ex e (lower cost) → Zone 1 small/medium cabinets — choose Ex d (reliable) → large cabinets / high power / need for standard components — choose Ex p (flexible). Zhejiang Golden Unicorn provides selection advice based on project conditions; explosion-proof products are supplied in joint supply with an Ex-qualified manufacturer.
FAQ FAQ
Can standard PLCs be used in an explosion-proof control cabinet?
Yes, inside an Ex p pressurized cabinet(after purge is complete and internal positive pressure is established); not inside Ex d / Ex e cabinets — certified explosion-proof components are mandatory there.
Which type is most common in Zone 1?
Ex d flameproofIt is the most common; control boxes, pushbutton boxes, and distribution boxes are mostly flameproof for Zone 1.
Can contactors be installed in an increased-safety cabinet?
No. Contactor breaking produces an arc, so it can only be installed in a flameproof enclosure or replaced with a contactless solution (solid-state relays require a temperature-rise evaluation).
What should be done after a power outage on a pressurized cabinet?
After a power outage the cabinet loses positive pressure. Before re-energizing, it must bepurged againand only after the specified purge time is reached and the interlock confirms it can power be applied.
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