Which type of transformers require specific installation distances from building surfaces?

Flammable-liquid or oil-filled transformers necessitate specific installation distances from building surfaces due to safety concerns related to fire hazards. These transformers are filled with combustible liquids, which can pose significant risks if they leak or spill. The installation requirements for these transformers often include maintaining a minimum distance from structures to reduce the risk of fire spreading to nearby buildings or other combustible materials. Additionally, these distances help ensure that any potential spills can be contained and managed appropriately, minimizing the danger to both people and property.

In contrast, other types of transformers, such as single-phase, dry-type, and three-phase transformers, have different safety and installation requirements that do not typically involve the same level of risk associated with combustible materials. This makes the correct option crucial for adhering to safety regulations and protecting the surrounding environment.