Electrical Safety Clearance for Transformer
September 2, 2012 11 Comments
Electrical Safety Clearance for Transformer:
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 surroundingStructure 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 |
JIGNESH PARMAR
Thanks a lot for being with us
thanks a lot mr Jignesh.Parmar
Thanks, it would be nice to see the specific NEC references you are making – ie what section, table etc of NEC. Thanks.
I have three grey garbage-can shape transformers on the wooden pole behind my backyard. It is about 60ft away from my bed room. My wife and I have some concerns about EMF coming from them. One of them is labeled 100 on the body and the other two are 75 each. I have no idea the meaning of the numbers. If my wife is pregnant, should we concern about the EMF? By the way, we are located in Chicago. Thank you for your help!
Good ,easy to learn
These tables look great, but I do not find the listed clearances in either NEC or NES. The NES paragraphs sited do not exist in the 2012 issue of IEEE C2. Please provide correct references for listed clearances. Thank you!
I am living Guwahati in Assam, a residancial area, i need a suggestions from your side . Our colony commutee is installing a transformar in front my veicle exited gate. So what can i do?
is there any minimum distance required from main road for installing bed mounted transformer and what will be the maximum distance that we can place the transformer inside the main road.
Dear sir,
In which distance between two transformers (in 132 kv switch yard), there is not require a trafo baffle wall.?
Regards.
How much should be the roof clearance for 1000 KV Oil cooled transformer. It is having Oil Conservator tank top mounted.
What is the voltage level of DT to be shifted apart from building