Clearance Tables
- Clearance from Outdoor Liquid Insulated Transformers to Buildings (NEC)
- Clearance between Two Outdoor Liquid Insulated Transformers (NEC)
- Dry Type Transformer in Indoor Installation (NES 420.21)
- Dry Type Transformer in Outdoor Installation (NES 420.22)
- Non Flammable Liquid-Insulated Transformer in Indoor Installation (NES 420.21)
- Oil Insulated Transformer in Indoor Installation (NES 420.25)
- Transformer Clearance from Building (IEEE Stand.)
- Transformer Clearance Specifications (Stand. Georgia Power Company)
- Clearance of Transformer-Cable-Overhead Line (Stand. Georgia Power Company)
Clearance from Outdoor Liquid Insulated Transformers to Buildings (NEC)
| Liquid | Liquid Volume (m3) | Fire Resistant Wall | Non-Combustible Wall | Combustible Wall | Vertical Distance |
| Less Flammable | NA | 0.9 Meter | 0.9 Meter | 0.9 Meter | 0.9 Meter |
| <38 m3 | 1.5 Meter | 1.5 Meter | 7.6 Meter | 7.6 Meter | |
| >38 m3 | 4.6 Meter | 4.6 Meter | 15.2 Meter | 15.2 Meter | |
| Mineral Oil | <1.9 m3 | 1.5 Meter | 4.6 Meter | 7.6 Meter | 7.6 Meter |
| 1.9 m3 to 19 m3 | 4.6 Meter | 7.6 Meter | 15.2 Meter | 15.2 Meter | |
| > 19 m3 | 7.6 Meter | 15.2 Meter | 30.5 Meter | 30.5 Meter |
Clearance between Two Outdoor Liquid Insulated Transformers (NEC)
| Liquid | Liquid Volume (m3) | Distance |
| Less Flammable | NA | 0.9 Meter |
| <38 m3 | 1.5 Meter | |
| >38 m3 | 7.6 Meter | |
| Mineral Oil | <1.9 m3 | 1.5 Meter |
| 1.9 m3 to 19 m3 | 7.6 Meter | |
| > 19 m3 | 15.2 Meter |
Dry Type Transformer in Indoor Installation (NES 420.21)
| Voltage | Distance (min) |
| Up to 112.5 KVA | 300 mm (12 in.) from combustible material unless separated from the combustible material by a heat-insulated barrier. |
| Above 112.5 KVA | Installed in a transformer room of fire-resistant construction. |
| Above 112.5 KVA with 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 |
Dry Type Transformer in Outdoor Installation (NES 420.22)
| Voltage | Distance (min) |
| Above 112.5 KVA with 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 |
Non Flammable Liquid-Insulated Transformer in Indoor Installation (NES 420.21)
| Voltage | Distance (min) |
| Over 35KV | Installed 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 KVA | Installed 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 |
Oil Insulated Transformer in Indoor Installation (NES 420.25)
| Voltage | Distance (min) |
| Up to 112.5 KVA | Installed indoors Vault (With construction of reinforced concrete that is not less than 100 mm (4 in.) thick. |
| Up to 10 KVA & Up to 600V | Vault shall not be required if suitable arrangements are made to prevent a transformer oil fire from igniting |
| Up to 75 KVA & Up to 600V | Vault 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 |
Transformer Clearance from Building (IEEE Stand)
| Transformer | Distance from Building (min) |
| Up to 75 KVA | 3.0 Meter |
| 75 KVA to 333 KVA | 6.0 Meter |
| More than 333 KVA | 9.0 Meter |
Transformer Clearance Specifications (Stand: Georgia Power Company)
| Description of Clearance | Distance (min) |
| Clearance in front of the transformer | 3.0 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 building | 4.2 Meter |
| The edge of the concrete transformer pad to nearest building wall, windows, or other openings | 3.0 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 hydrants | 1.8 Meter |
| The water’s edge of a swimming pool or any body of water. | 4.5 Meter |
| Facilities used to dispense hazardous liquids or gases | 6.0 Meter |
| Facilities used to store hazardous liquids or gases | 3.0 Meter |
| Clear vehicle passageway at all times, immediately adjacent of Transformer | 3.6 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. |
Clearance of Transformer-Cable-Overhead Line (Stand: Georgia Power Company)
| Description of Clearance | Horizontal Distance (mm) | ||
| to pad-mounted transformers | to buried HV cable | to overhead HV Line | |
| Fuel tanks | 7.5 Meter | 1.5 Meter | 7.5 Meter |
| Granaries | 6.0 Meter | 0.6 Meter | 15 Meter |
| Homes | 6.0 Meter | 0.6 Meter | 15 Meter |
| Barns, sheds, garages | 6.0 Meter | 0.6 Meter | 15 Meter |
| Water wells | 1.5 Meter | 1.5 Meter | 15 Meter |
| Antennas | 3.0 Meter | 0.6 Meter | Height of Antenna + 3.0 Meter |
Related electrical guides & articles
What should be the minimum distance clearance between the two 2000 KVA liquids insulated indoor transformers?
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.
for the finalization of the distribution transformer 2/2.5/3.15 MVA rating what are the main considerable points to finalize?
Please let me know the Minimum distance required between 33KV HT underground cable and 200LPM gas bank.
SEPARATION DISTANCE BETWEEN 1600 KVA 11/433V OIL COOLED TRANSFORMERS AND 500 KVA DG ST
Please let ne know the minimum clearance between 33/.415kv,200 kva transformer to Oil pipeline .
Is there any standards available for this clearance ?
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
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
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.
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