1. How mining-duty control cabinets differ from surface control cabinets (Group I assessment system)
The enemies underground aremethane + coal dust + moisture + impact. Mining-duty control cabinets are assessed to GB 3836 Group I, with the explosion-proof marking Ex d I(no gas group or temperature class is marked; the design assumes a methane + coal dust atmosphere throughout); enclosures are mainly welded steel plate, with higher impact resistance than surface die-cast aluminum boxes; going underground also requires MA coal mine safety certification.
2. Flameproof joint requirements (width × gap × roughness)
The flameproof joint is the critical point of a mining-duty cabinet. GB 3836.2 imposes three constraints on flat joints:
| Parameter | Requirement | What it should show |
|---|---|---|
| Joint width L | Banded by volume (e.g. ≥ 25mm) | The larger the volume, the wider the permitted gap |
| Maximum gap W | By width (e.g., ≤ 0.5 mm for 25 mm wide joints; Class I is stricter) | Flame is quenched in the narrow gap |
| Surface roughness | Fine machining (Ra ≤ 6.3 μm class) | Prevents flame transmission through gap leakage |
Maintenance discipline: flameproof joints may only be lightly coated with rust-preventive oil (or phosphated);no grinding, no painting, no gaskets; on reassembly after service, tighten in diagonal sequence to original torque and record gap spot checks.
3. Cable Entry Requirements (bell mouth + MT 818 cable)
- Entry device: mining-duty cable gland (compression nut type / pressure plate type), with elastic seal ring + metal washer; one seal ring accepts only one MT 818 mining flame-retardant cable;
- Seal ring inner diameterinterference fit with cable outer diameter; cutting the ring to enlarge the bore or wrapping tape as compensation is a violation;
- Spare entries: all sealed with matching threaded plugs; a mandatory inspection item;
- Armored cable: entry device must have an armor clamping structure to prevent cable pull-out.
4. MA Certification and Factory Inspection (dual certificates for underground entry)
Compliant combination for mining-duty control cabinets:Explosion-proof certificate (Ex d I) + Mining Product Safety Mark (MA), with the MA number cast on the nameplate and verifiable on the Safety Mark Center official website. Factory inspection focuses on: flameproof enclosurehydrostatic testreport, flameproof joint parameter spot checks, and completeness of entry device accessories. Zhejiang Golden Unicorn undertakes mining-duty explosion-proof requirements throughjoint supply with an Ex-qualified manufacturer, with complete documentation shipped with the goods.
5. Acceptance and Inspection Checklist (before and after going underground)
On delivery acceptance: ① explosion-proof certificate + MA certificate numbers match and are within validity; ② flameproof joints free of rust, paint, or impact damage; ③ bell mouth quantity and diameter match cables, threaded plugs in place; ④ hydrostatic test report and factory inspection report complete.Operating inspection: ⑤ visual check of bolts and seals every shift; ⑥ monthly dedicated measurement of flameproof joint gaps and grounding continuity; ⑦ after service, records filed per GB/T 3836.13 repair specifications.
FAQ FAQ
Are the requirements the same for mining-duty control cabinets and mining-duty distribution boxes?
Explosion-proof requirements share the same origin (Ex d I + MA); control cabinets also involveintrinsically safe control circuits / flameproof pushbuttonsand the matching certification of such components, making the component list more complex.
What if the flameproof joint surface gets damaged?
Minor scratches are assessed per the GB/T 3836.13 repair specification; flameproof joint surfaces with damage beyond tolerancecannot be repaired and put back into service, and must be returned to the factory or the enclosure replaced.
Can surface cable be used underground?
No. Cables entering the mine must be MT 818 mining-duty flame-retardant cable (with the MA mark on the sheath); ordinary cable will burn and spread the fire along the roadway.
What are the rules for applying anti-rust oil to flameproof joint surfaces?
Applya thin coat of non-acidic anti-rust oil. Do not apply thick grease (it collects dust), and never apply paint — the coating changes the fit characteristics of the flameproof joint surface.
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