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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.

31 Comments


  1. Atindra Das
    Nov 14, 2023

    please share fire safety requirement for oil type inddor transformer for 2mVA.


  2. 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?


  3. Papia Ray
    Jun 08, 2023

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


  4. Khalid Khan
    Dec 12, 2022

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


  5. 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.


  6. 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?


  7. karthikeyan
    Mar 30, 2022

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


  8. RADHAKRISHNAN
    Mar 03, 2022

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


  9. 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 ?


  10. 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


  11. 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


  12. 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.


  13. 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


  14. Faseeh Shan
    Jan 23, 2020

    What should be the safe distance of a transformer from the Control system(PLC) Cabinet. So that it may not effect(4 to 20mAmp) Control signals


  15. Joseph
    Dec 05, 2019

    what are the pros/cons in stacking indoor transformers?


  16. TODARMAL Panwar
    Apr 02, 2019

    Sir contractor 440 volt transformers installed closer to my house please suggest me how distance between home and transformers


  17. P RAGHAVEDRARAO
    Mar 15, 2019

    UP TO WHAT CAPACITY FIRE PROTECTION WALL REQUIRED FOR OIL FILLED POWER TRANSFORMERS


  18. Bappadityo Goswami
    Dec 28, 2018

    Dear Sir,
    Please provide the NEC reference Number regarding minimum distance between two outdoor transformer?


  19. Prasenjit Sardar
    Oct 13, 2017

    I live in an apartment and from the electric office a transformer is being planted very near my building and outside my window. So , in this circumstance what should I do and what should be the check points and for complain where sholud I lodge them? Please help. Awaiting your early response.


    • AMITABHA GUHA
      Feb 04, 2018

      Mr. Prasenjit Sardar, I have an exactly similar problem. Have you got answer to your problem from any source ? If yes, please let me know the details as it will help me a lot. I am particularly interested to know what should be the minimum distance they should maintain from building line / property line for a 6 KV / 430 V transformer ?


  20. Abhijit Bhavsar
    Feb 24, 2017

    Dear Sir,
    We are installing Dry type transformer of capacity 2750 KVA (11KV/433 V) inside the container with DNV certified 2.7.2 Pressurized container as the area is hazardous area Please suggest what should be the minimum distance of the transformer from the walls of the container. the walls of the container is of class A60. Also suggest the distance between two transformer as we are placing 2 transformer on the same offshore platform.


  21. Mostafa elsissy
    Aug 21, 2016

    What is the max # of transformer can be located in one room with respect to fire/safety


  22. Mustafa Elsissy
    Aug 01, 2016

    Thanks for the valuable information and my comment is what is the fire min separation distance between TRFS located inside closed space?


  23. choi
    Jan 23, 2016

    Thanks for the useful article.

    Could you let me know “NES”??

    In the middle of the article, there is “NES 420.22 -Dry type transformaer”.

    Is this the first letter of National Electric Safety Code? or Something?

    I would really appreciate your help.


  24. Alex
    Jan 07, 2016

    I would use both measurement units, Imperial and metric?
    Also you should have referenced NFPA 850, UL and FM global.

    Thanks,
    A.


  25. David
    Dec 02, 2015

    For tables 1 and 2, where exactly is this table referencing in the NEC? I’ve scoured all over article 450 and I don’t see anything with specific distances.


  26. Sanjiv Batra
    May 13, 2015

    Hello,
    Two days back punjab state elect. Board put on of tranceformer in front of my residental plot. The clearence from my plot to tranceformer pole is about 6 inches. I was planning to start construction this month. I want that traceformer should be fitted on some where else. Please can you advise how i can proceed. Do you have legal information about this issue. Even i planned to sale this plot but no one like to buy this plot.

    thanks


  27. folskan
    Dec 16, 2013

    gracias desde honduras


  28. SANATH JAMES
    Dec 24, 2012

    This is a very useful web site providing and sharing the design standards pertaining to electrical engineering. Recommeded for all serious electrical engineers.

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