⚡ Electrical Machinery in Mines – DGMS Approval & Safety Requirements

Electrical machinery used in mines must comply with strict DGMS rules due to high risk of:

• Methane ignition
• Coal dust explosion
• Electrical shock
• Fire hazards
• Overheating
• Arcing

DGMS ensures that only safe, certified & tested equipment is allowed underground. This blog explains the full DGMS approval process, standards, safety rules, installation requirements & EX certifications.

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🔹 1. What is Electrical Machinery in Mines? Electrical machinery includes all equipment that uses electricity for:

• Haulage
• Pumping
• Ventilation
• Lighting
• Communication
• Gas detection
• Drilling
• Coal loading
• Mine operation

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🔹 2. Why DGMS Approval is Mandatory? Because electrical machinery can produce:

• Sparks
• Heat
• Arcs
• Short-circuits

In methane-rich underground mines, even a tiny spark can cause an explosion. DGMS approval ensures equipment: 

✔ Is safe for explosive atmospheres
✔ Follows BIS/IEC standards
✔ Undergoes rigorous testing
✔ Performs safely in methane/dust zones

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🔹 3. Categories of Electrical Equipment Requiring DGMS Approval 

  ⭐ A. Flameproof (Ex-d) Equipment Used in Zone 1 & Zone 2
Examples:

• Motors
• Switchgear
• Transformers
• Glands
• Starters

⭐ B. Intrinsically Safe (Ex-ia / Ex-ib) Equipment Used in Zone 0 / Zone 1 / Zone 2
Examples:

• Gas detectors
• Cap lamps
• Telemetry sensors

⭐ C. Non-Sparking (Ex-n) Equipment Used in Zone 2
Examples:

• IS lighting
• Surface motors near explosive areas

⭐ D. Ordinary Electrical Equipment Used only in:

• Surface mines
• Non-gassy areas
• Workshops

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🔹 4. Standards Used by DGMS

Equipment Type	Standard
FLP	IS/IEC 60079-1
IS	IS/IEC 60079-11
Gas detectors	IS 8784 / IECEx
Cables	IS 1554 / IS 7098
Lighting	IS/IEC 60079-7
Switchgear	IS 8623
Earth leakage	IS 5720
General EX	IS 5572 / IS 13408

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🔹 5. DGMS Approval Process for Electrical Machinery

The approval process is multi-stage: Manufacturer / IAR ↓ Submit Application (Form B / Form C) ↓ DGMS Scrutiny of Documents ↓ Testing at CIMFR / CPRI / ERTL / ETDC ↓ Factory Audit (QAR) ↓ Field Trial (if required) ↓ DGMS Final Approval (Form K)

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🔹 6. Documents Required by DGMS Mandatory documents:

• Technical drawings
• Bill of materials
• FLP/IS certification
• IECEx / ATEX / BIS license
• QAR / QAN
• Flamepath drawings
• Electrical schematic
• Mechanical drawings
• User manual
• Routine test reports

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🔹 7. Testing Required for DGMS Electrical Approval 

  ⭐ A. FLP Equipment Tests

• Flame transmission test
• Internal explosion test
• Temperature rise test
• Impact test
• Pressure withstand test
• Flamepath measurement
• Degree of protection (IP)

⭐ B. IS Equipment Tests

• Intrinsic safety test
• Fault simulation test
• Capacitive/Inductive energy limitation
• Circuit stability test
• Thermal tests

⭐ C. General Electrical Tests

• HV test
• Insulation resistance
• Earthing checks
• Cable gland test

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🔹 8. Installation Requirements According to DGMS 

 Electrical machinery must follow:

✔ Proper earthing

• 2 separate earthing conductors
• Earth resistance < 1 ohm

✔ Cable protection

• Fire-resistant cables
• Proper joints & glands
• No loose connections

✔ Overload & Earth-Leakage Protection

• ELCB mandatory
• Automatic tripping at faults

✔ Adequate ventilation Prevents overheating. ✔ Weekly inspection by Electrical Supervisor (ER-1961)

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🔹 9. Statutory Requirements from Indian Regulations Coal Mines Regulations (CMR 2017)

• Reg. 131: Danger from Electricity
• Reg. 132: Precautions against shock
• Reg. 133: Switchgear
• Reg. 136: ELCB
• Reg. 138: Earthing

Electrical Rules, 2005 Applies for:

• Installations
• Maintenance
• Protection systems

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🔹 10. Non-Compliance Consequences Failure to comply leads to:

• Suspension of DGMS approval
• Withdrawal of approval
• Mine closure orders
• Penalties
• Accidents & explosions
• Criminal liability for manager & owner

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🔥 25 MCQs (DGMS Pattern) with Answers

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1) Flameproof equipment is tested as per — a) IS 2062
b) IS 732
c) IS/IEC 60079-1
d) IS 770
e) None
Ans: c

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2) Intrinsic safety is defined under —

a) IS 13408
b) IS/IEC 60079-11
c) IS 5572
d) CMR 106
e) None
Ans: b

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3) DGMS approval is issued in —

a) Form B
b) Form L
c) Form K
d) Form P
e) None
Ans: c

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4) Zone 1 equipment must be —

a) Domestic
b) Ex-d / Ex-ia / Ex-ib
c) Ex-n
d) None
Ans: b

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5) Gas detectors are generally —

a) Ex-d
b) Ex-ia
c) Non-sparking
d) Ordinary
e) None
Ans: b

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6) Flamepath must be —

a) Painted
b) Smooth & within tolerance
c) Corroded
d) Dark
e) None
Ans: b

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7) Factory audit for DGMS approval is —

a) Recreational
b) Optional
c) Mandatory (QAR)
d) Festival work
e) None
Ans: c

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8) Electrical shock prevention in mines requires —

a) Switch off lights
b) Proper earthing
c) More ventilation
d) Spray water
e) None
Ans: b

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9) Ex-n equipment allowed in —

a) Zone 0
b) Zone 1
c) Zone 2
d) All zones
e) None
Ans: c

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10) Flameproof equipment used to prevent —

a) Heat loss
b) Gas ignition
c) Cooling
d) Insulation
e) None
Ans: b

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11) ELCB is mandatory under —

a) Reg. 105
b) Reg. 136 (CMR 2017)
c) Reg. 200
d) IS 13703
e) None
Ans: b

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12) Temperature rise test ensures —

a) Colour
b) Price
c) Safe heating levels
d) Gland quality
e) None
Ans: c

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13) Ex-ia can withstand —

a) One fault
b) Zero fault
c) Two independent faults
d) Five faults
e) None
Ans: c

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14) Electrical machinery without DGMS approval is —

a) Allowed
b) Illegal
c) Optional
d) Seasonal
e) None
Ans: b

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15) IS equipment prevents ignition by —

a) Thick steel
b) Limiting energy
c) Force
d) Weight
e) None
Ans: b

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16) Flameproof enclosure prevents —

a) Water
b) Heat
c) Flame escape
d) Rust
e) None
Ans: c

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17) Standby earth conductor is —

a) Forbidden
b) Mandatory
c) Optional
d) Not required
e) None
Ans: b

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18) Cable glands for FLP must be —

a) PVC
b) Steel
c) FLP certified
d) Domestic
e) None
Ans: c

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19) Gas detector calibration required —

a) Annually
b) Monthly
c) Every 5 years
d) Randomly
e) None
Ans: b

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20) Testing for ELCB is —

a) Unnecessary
b) Mandatory weekly
c) Optional
d) Only yearly
e) None
Ans: b

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21) Electrical rules applicable in mines —

a) Housing rules
b) Fishing rules
c) Electricity Rules 2005
d) Restaurant rules
e) None
Ans: c

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22) Transformer underground must be —

a) Oil-cooled
b) Dry type FLP
c) Water-cooled
d) Air-cooled
e) None
Ans: b

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23) Cap lamps used in mines are —

a) Ordinary LED
b) IS-approved safety lamps
c) Desk lamps
d) Tube lights
e) None
Ans: b

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24) DGMS testing includes —

a) GST audit
b) Salary verification
c) Electrical safety tests
d) Coal testing
e) None
Ans: c

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25) Goal of DGMS electrical rules —

a) Increase company profit
b) Reduce manpower
c) Ensure safe electrical installations in mines
d) Decoration
e) None
Ans: c

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🔚 Conclusion 

Electrical machinery forms the backbone of safe mining operations.
DGMS ensures that all equipment—motors, switchgear, transformers, cap lamps, gas detectors—meet Flameproof / Intrinsic Safety / EX standards. Understanding DGMS approval, installation rules & EX protection is essential for:

• Electrical Supervisors
• Engineers
• Safety Officers
• DGMS exam aspirants
• Manufacturers

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