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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)
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6. Oil Insulated Transformer in Indoor Installation (NES 420.25)
7. Transformer Clearance from Bui lding (IEEE Stand.)
8. Transformer Clearance Specificat ions (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
Wall
Combustible
Wall
Vertical
Distance
Less
Flammable
NA 0.9 Meter 0.9 Meter 0.9 Meter 0.9 Meter
38 m3 4.6 Meter 4.6 Meter 15.2 Meter15.2
Meter
Mineral
Oil
19 m3 7.6 Meter 15.2 Meter 30.5 Meter 30.5Meter
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Clearance between Two Outdoor Liquid Insulated Transformers (NEC
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Liquid Liquid Volume (m3) Distance
Less
Flammable
NA 0.9 Meter
38 m3 7.6 Meter
Mineral Oil
19 m3 15.2 Meter
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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 KVAInstalled 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
Go to Content ↑
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
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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-resistantconstruction.
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
Go to Content ↑
Oil Insulated Transformer in Indoor Installation (NES 420.25)
Voltage Distance (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 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
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Transformer Clearance from Building (IEEE Stand)
Transformer Distance from Building (min)
Up to 75 KVA 3.0 Meter
75 KVA to 333
KVA6.0 Meter
More than 333 KVA 9.0 Meter
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Transformer Clearance Specifications (Stand: Georgia Power
Company)
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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 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 hydrants 1.8 Meter
The water’s edge of a swimming pool or any body of
water.4.5 Meter
Facil it ies used to dispense hazardous l iquids 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 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 sideof 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
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
Go to Content ↑
Recommended EE articles
jiguparmar - Jignesh Parmar has completed his B.E(Electrical) from Gujarat
University. He is member of Institution of Engineers (MIE),India. Membership No:M-
1473586.He has more than 12 years experience in Transmission -Distribution-
Electrical Energy theft detection-Electrical Maintenance-Electrical Projects (Planning-
Designing-Technical Review-coordination -Execution). He is Presently associate with
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