Safety Clearance for Transformer

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

 

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About Jignesh.Parmar
Jignesh Parmar has completed his B.E(Electrical) from Gujarat University. He has more than 11 years experience in Power Transmission-Power Distribution-Electrical energy theft detection-Electrical Maintenance-Electrical Projects(Planning-Designing-coordination-Execution). He is Presently associate with one of the leading business group as a Assistant Manager at Ahmedabad,India. He is Freelancer Programmer of Advance Excel and design useful Excel Sheets of Electrical Engineering as per IS,NEC,IEC,IEEE codes. He is technical Author for "Electrical Mirror" and "Electrical India" Magazines. He is Technical Blogger and Familiar with English, Hindi, Gujarati, French languages. He wants to Share his experience & knowledge and help technical enthusiasts to find suitable solutions and updating themselves on various Engineering Topics.

6 Responses to Safety Clearance for Transformer

  1. biswa says:

    Thanks a lot for being with us

  2. adel lotfi says:

    thanks a lot mr Jignesh.Parmar

  3. Matt W says:

    Thanks, it would be nice to see the specific NEC references you are making – ie what section, table etc of NEC. Thanks.

  4. Ben Johnson says:

    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!

  5. nixon says:

    Good ,easy to learn

  6. Pat L. says:

    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!

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