1. Group I Environments: Underground Coal Mines (Methane + Coal Dust)
Underground coal mines presentmethane (firedamp) and coal dustdual explosion risk, plus confined spaces, moisture, and rockfall impact. Mining-duty electrical equipment is therefore assessed separately under GB 3836 Group I: the explosion-proof marking is written directly as Ex d I(no gas group or temperature class is marked, because Group I is uniformly assessed against methane).
2. MA Coal Mine Safety Certification (Mining Product Safety Mark)
Electrical equipment taken underground must carryan MA mark issued by the National Mining Product Safety Mark Center:
- The product first passes explosion-proof testing (Ex d I) + mining-specific assessment (impact, drop, moisture);
- after the MA certificate is obtained,the MA mark and number are cast into the nameplate, verifiable on the Safety Mark Center's official website;
- at procurement, check that the MA certificate'smodel, validity period, and manufacturerall match;
- underground use also requires filing and inspection with the local coal mine safety supervision department.
3. Structural Differences vs. Above-Ground Explosion-Proof Boxes (more robust, more moisture-resistant)
| Item | Explosion-proof ground box | Mining-duty explosion-proof box |
|---|---|---|
| Ex marking | Ex d ⅡB T4 Gb | Ex d I |
| Certifications | Ex certificate + 3C | Ex certificate + MA mark |
| Enclosure | Cast aluminum / stainless steel | Primarily welded steel plate, impact-resistant |
| Cable | Standard flame-retardant / armored | MT 818 mining-duty flame-retardant cable |
4. Mining Cable Entry Requirements (MT 818 + cable gland)
Common name for the cable entry device on a mining-duty distribution boxcable gland, available in compression nut and compression plate types. When used with MT 818 mining-duty flame-retardant cable (such as MYP shielded rubber-sheathed flexible cable), the following is required:
- The sealing ring inner diameter must match the cable outer diameter,one sealing ring per cable;
- The compression plate type entry device requires a metal washer to prevent the cable from being pulled out;
- After tightening the cable gland, an 8–10mm compression allowance must remain;
- High-voltage armored cable entryrequires a cast-sealed entry device with armor fixing.
5. Purchase Verification Checklist (6 items before going underground)
① Ex d I explosion-proof certificate; ② MA mark certificate (verifiable on the official website, within validity period); ③ nameplate MA number matches the certificate; ④ no visible deformation of the enclosure, no corrosion on flameproof surfaces; ⑤ number and diameter of entry devices match the cable; ⑥ accompanying documents (manual, inspection report, system diagram) complete. Mining-duty products are supplied by Zhejiang Golden Unicorn through joint supply with an Ex-qualified manufacturer.
FAQ FAQ
Can a mining-duty explosion-proof box be used without the MA mark?
It cannot go underground. The MA mark is a mandatory threshold for coal mine safety. Equipment without the MA mark is strictly prohibited for underground use, and coal mine safety inspectors will reject it outright.
What is the relationship between Ex d I and Ex d IIB?
Class I specifically refers tocoal mine methane environments, with no group or temperature class marking; IIB is a surface Class II gas group. The two certifications are independent and cannot substitute for each other.
Why must mining cables be flame-retardant?
A single cable fire underground can ignite methane and spread through the entire tunnel. MT 818 flame-retardant cableself-extinguishesafter the ignition source is removed, blocking fire spread.
What should be checked during underground distribution box inspections?
Flameproof surface corrosion, bolt tightness, sealing ring aging, cable gland compression allowance, grounding continuity — visual inspection every shift and a dedicated check monthly are recommended.
Related pages:Technical notes · Products · Industries · Resource center · FAQ · Get a quote