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Home / Technical Articles / Safety Clearance Recommendations for Transformer
Safety Clearance Recommendations for Transformer
Safety Clearance Recommendations for Transformer (on photo 10/0.4 kV transformer substation by FIMA)

Clearance Tables

  1. Clearance from Outdoor Liquid Insulated Transformers to Buildings (NEC)
  2. Clearance between Two Outdoor Liquid Insulated Transformers (NEC)
  3. Dry Type Transformer in Indoor Installation (NES 420.21)
  4. Dry Type Transformer in Outdoor Installation (NES 420.22)
  5. Non Flammable Liquid-Insulated Transformer in Indoor Installation (NES 420.21)
  6. Oil Insulated Transformer in Indoor Installation (NES 420.25)
  7. Transformer Clearance from Building (IEEE Stand.)
  8. Transformer Clearance Specifications (Stand. Georgia Power Company)
  9. Clearance of Transformer-Cable-Overhead Line (Stand. Georgia Power Company)

Clearance from Outdoor Liquid Insulated Transformers to Buildings (NEC)

LiquidLiquid Volume (m3)Fire Resistant Wall Non-Combustible WallCombustible WallVertical Distance
Less FlammableNA0.9 Meter0.9 Meter0.9 Meter0.9 Meter
<38 m31.5 Meter1.5 Meter7.6 Meter7.6 Meter
>38 m34.6 Meter4.6 Meter15.2 Meter15.2 Meter
Mineral Oil<1.9 m31.5 Meter4.6 Meter7.6 Meter7.6 Meter
1.9 m3 to 19 m34.6 Meter7.6 Meter15.2 Meter15.2 Meter
> 19 m37.6 Meter15.2 Meter30.5 Meter30.5 Meter

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Clearance between Two Outdoor Liquid Insulated Transformers (NEC)

LiquidLiquid Volume (m3)Distance
Less FlammableNA0.9 Meter
<38 m31.5 Meter
>38 m37.6 Meter
Mineral Oil<1.9 m31.5 Meter
1.9 m3 to 19 m37.6 Meter
> 19 m315.2 Meter

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Dry Type Transformer in Indoor Installation (NES 420.21)

VoltageDistance (min)
Up to 112.5 KVA300 mm (12 in.) from combustible material unless separated from the combustible material by a heat-insulated barrier.
Above 112.5 KVAInstalled in a transformer room of fire-resistant construction.
Above 112.5 KVA with Class 155 Insulationseparated from  a fire-resistant barrier not less than 1.83 m (6 ft) horizontally and 3.7 m (12 ft) vertically

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Dry Type Transformer in Outdoor Installation (NES 420.22)

VoltageDistance (min)
Above 112.5 KVA with Class 155 Insulationseparated from  a fire-resistant barrier not less than 1.83 m (6 ft) horizontally and 3.7 m (12 ft) vertically

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Non Flammable Liquid-Insulated Transformer in Indoor Installation (NES 420.21)

VoltageDistance (min)
Over 35KVInstalled indoors Vault (Having liquid confinement area and a pressure-relief vent for absorbing any gases generated by arcing inside the tank, the pressure-relief vent shall be connected to a chimney or flue that will carry such gases to an environmentally safe area
Above 112.5 KVAInstalled in a transformer room of fire-resistant construction.
Above 112.5 KVA (Class 155 Insulation)separated from a fire-resistant barrier not less than 1.83 m (6 ft) horizontally and 3.7 m (12 ft) vertically

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Oil Insulated Transformer in Indoor Installation (NES 420.25)

VoltageDistance (min)
Up to 112.5 KVAInstalled indoors Vault (With construction of reinforced concrete that is not less than 100 mm (4 in.) thick.
Up to 10 KVA & Up to 600VVault shall not be required if suitable arrangements are made to prevent a transformer oil fire from igniting
Up to 75 KVA & Up to 600VVault shall not be required if where the surrounding Structure is classified as fire-resistant construction.
Furnace transformers (Up to 75 kVA)Installed without a vault in a building or room of fire resistant construction

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Transformer Clearance from Building (IEEE Stand)

TransformerDistance from Building (min)
Up to 75 KVA3.0 Meter
75 KVA to 333 KVA6.0 Meter
More than 333 KVA9.0 Meter

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Transformer Clearance Specifications (Stand: Georgia Power Company)

Description of ClearanceDistance (min)
Clearance in front of the transformer3.0 Meter
Between Two pad mounted transformers (including Cooling fin)2.1  Meter
Between Transformer and Trees, shrubs, vegetation( for unrestricted natural cooling )3.0 Meter
The edge of the concrete transformer pad to nearest the building4.2 Meter
The edge of the concrete transformer pad to nearest  building wall, windows, or other openings3.0 Meter
Clearance from the transformer to edge of (or Canopy) building (3 or less stories)3.0 Meter
Clearance in front of the transformer doors and on the left side of the transformer, looking at it from the front (For operation of protective and switching devices on the unit)3.0 Meter
Gas service meter relief vents.0.9 Meter
Fire sprinkler values, standpipes and fire hydrants1.8 Meter
The water’s edge of a swimming pool or any body of water.4.5 Meter
Facilities used to dispense hazardous liquids or gases6.0 Meter
Facilities used to store hazardous liquids or gases3.0 Meter
Clear vehicle passageway at all times, immediately adjacent of Transformer3.6 Meter
Fire safety clearances can be reduced by building a suitable masonry fire barrier wall (2.7 Meter wide and 4.5 Meter Tall) 0.9 Meter from the back or side of the Pad Mounted Transformer  to the side of the combustible wall
Front of the transformer must face away from the building.

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Clearance of Transformer-Cable-Overhead Line (Stand: Georgia Power Company)

Description of ClearanceHorizontal Distance (mm)
to pad-mounted transformersto buried HV cableto overhead HV Line
Fuel tanks7.5 Meter1.5 Meter7.5 Meter
Granaries6.0 Meter0.6 Meter15 Meter
Homes6.0 Meter0.6 Meter15 Meter
Barns, sheds, garages6.0 Meter0.6 Meter15 Meter
Water wells1.5 Meter1.5 Meter15 Meter
Antennas3.0 Meter0.6 MeterHeight of Antenna + 3.0 Meter

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author-pic

Jignesh Parmar

Jignesh Parmar has completed M.Tech (Power System Control), B.E (Electrical). He is member of Institution of Engineers (MIE), India. He has more than 20 years experience in transmission & distribution-energy theft detection and maintenance electrical projects.

30 Comments


  1. Binoy
    Jul 26, 2023

    can I fix the transformer above the private road in a villa project by making a concrete slab and taking other required precaution?


  2. Papia Ray
    Jun 08, 2023

    A new transformer is installing in front of my residencial boundary wall. Is it legal?


  3. Khalid Khan
    Dec 12, 2022

    What should be the minimum distance clearance between the two 2000 KVA liquids insulated indoor transformers?


  4. Dean Philips
    Oct 19, 2022

    Could you provide clause references for the first two tables? I cannot find these clearances in the NEC (2020 edition). Also tables 3-5, labeled NES … are likely NEC. And, the similar question regarding the reference to an IEEE Standard.


  5. sunil goutham guntu
    Sep 08, 2022

    for the finalization of the distribution transformer 2/2.5/3.15 MVA rating what are the main considerable points to finalize?


  6. karthikeyan
    Mar 30, 2022

    Please let me know the Minimum distance required between 33KV HT underground cable and 200LPM gas bank.


  7. RADHAKRISHNAN
    Mar 03, 2022

    SEPARATION DISTANCE BETWEEN 1600 KVA 11/433V OIL COOLED TRANSFORMERS AND 500 KVA DG ST


  8. Renjith
    Dec 29, 2021

    Please let ne know the minimum clearance between 33/.415kv,200 kva transformer to Oil pipeline .
    Is there any standards available for this clearance ?


  9. Subhash Jagota
    Oct 16, 2021

    Please, what should be the distance to be observed between a residential/office building to a 100 kv diesel power generator ..? Please what distance apart should be maintained


  10. Jude Elijah
    Apr 17, 2021

    Please, what should be the distance to be observed between a residential/office building to a 33 kv diesel power generator ..? Please what distance apart should be maintained


  11. GANESH JETHA
    Mar 17, 2021

    I WANT TO KNOW THE DISTANCE BETWEEN TWO 132 /33 KV 63 MVA X’MER IN THE GRID ( SUBSTATION ).WHAT IS RULE OF ELECTRICITY PLEASE SUGGEST.


  12. Naveed Alam
    Dec 20, 2020

    Dear sir,
    I want to construct house near a grid station
    What should be the horizontal safe distance of my house and heavy transformer of grid station.
    Thanks

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