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Recommendations for separation distances between outdoor transformer and buildings

Question asked by bcelikel on May 9, 2020

Hello Everybody,


One of our application transformer was located very close to control building. We are not able to keep required safety distance from transformer to the control building. So, we are looking for alternative solutions in order to comply NFPA 850 Standard. Our technical team proposed some solutions related with fire protection of building in a case of any failure on transformer (fire and explosion conditions). Some of these solutions have got disadvantages or some of them seems difficult to realize in terms of civil construction.


We would like to apply one of these solutions. Before applying one of these solutions, we would like to sure that the solutions that were proposed by our technical team in comply with NFPA 850 Standard. We have seen that some examples were given in NFPA 850. But, alternative solutions were not discussed or described.


In order to find best solution, Could you please comment on these alternative solutions with respect to NFPA 850 Standard?


We are also welcome to alternative solutions.


Thank you in advance. 


Best regards,




  • 1) Construction of the firewall with a length of 15m from the top of transformer as per shown Figure in NFPA 850 (In order not to change the construction material of roof and not to change windows) (Total height of firewall will be 18,66 m). Firewall height will be much more higher than the building. It looks statically not stable and very difficult to realize on the site. Please see Drawing-1
  • 2) Construction of the firewall to completely cover the building length (as per 15,38 m) (Firewall length is equal to height of building). It looks statically instable and difficult to realize.
  • 3) Replacing of roof material with fire-proof material and replacing the window glass and frame with ballistic and heat-resist material. There will be no action for extending the height of firewall.
  • 4) Replacing of roof material with fire-proof material and closing of existing windows with fire proof concrete Wall.
  • 5) The firewall will be extended in accordance with the condition when the tangent is drawn from the top of the transformer tank towards to the building from the corner of new firewall.(Although X = 15m distance is not provided). As you can see next drawing that the building seems to be protected from any explosion of transformer or split of oil fire just after explosion of transformer. Do you have any suggestion about this type of construction in order to protect the building and the roof from the fire? Please see Drawing-5
  • 6) The existing blast walls at three sides of the transformer will stay unchanged. Some reinforcement may be required to carry the additional load of the reinforced concrete sloped roof. Transformer explosion will be redirected away from the building. The building does not require any modifications. Please see Drawing-6. We have doubts about creepage distance between Transformer 154kV bushings and Reinforced Prefabricated Concrete Elements. We may have phase to earth fault due to height of bushings and 154 kV conductor connection to gantry. Please see-Drawing-6