Saturday, April 19, 2014

Spatial Clearances for Transformer Installation

Transformers are either installed indoors or outdoors. If two transformers are installed side-by-side, they shall be separated by fire-separation walls. Fire separation walls are deemed to be adequate even if oil capacity of individual transformers does not exceed 2000 litres, and total capacity of all transformers installed side by side exceeds 2000 litresNote 1. Ventilation is the most important thing to be ensured in indoor installations. The area required for ventilation is also specified as 2 m2 for outlet and 1 m2 for inlet per 1000 kVA of transformer capacityNote 2. This area is required for natural ventilation. If that much space is not physically available, fans may be used.

Vertical Clearance

Minimum clearance between the highest point of the conservator tank to the ceiling of the transformer room should be sufficient to remove the mounting on the transformer like the conservator. However, this clearance should not be less than 0.5 m Note 3.

Horizontal Clearance

Transformers shall be kept well away from walls. The minimum recommended spacing between the walls and transformer is shown in Fig 1 below.
Fig 1: Minimum horizontal clearances for transformers
 The wall indicated in the figure can also be fire separation wall. As such, there is no separate requirement for clearance from fire separation wall.

When fire safety is also taken into the picture, some more spatial clearances are to be observed. If transformer oil capacity is more than 2000 litres, the building housing the oil-filled transformer shall be separated by a distance of not less than 6 m from all other buildings Note 4. If however, a building is existing within 6 m, there shall not be any door or window opening in the substation or the adjacent building. Again, if such communication also exists, the substation shall be segregated by separating walls of 355 mm thick brick wall or 230 mm thick RCC, carried up to roof level. Doors, if any, shall be single fireproof with 2 h rating.

In the Code of Practice for Fire Safety: Electrical Installations (IS 1646), the minimum clearance specified is not in agreement with Code of Practice for Installation of Transformers (IS 10028 Part 2) when compared with Fig 1 reproduced from the latter standard. This specifies a minimum clearance of 750 mm (0.75 m) between the transformer or other apparatus and enclosing or separating walls Note 5. As is usual in the case of conflicts among provisions in standards, we may take the more stringent requirement of the two, which is, 1.25 m for transformers with enclosing walls on all four sides.

No mention of spatial clearances for transformers was found in the Indian Electricity Rules, 1956 and the Central Electricity Authority (Measures Relating to Safety and Electric Supply) Regulations, 2010.

American regulations seem to have included clear instructions on clearances as shown in this excellent article (Safety Clearance Recommendations for Transformer) on the Electrical Engineering Portal.


  1. Code of Practice for Selection, Installation and Maintenance of Transformers, Part 2 Installation, IS 10028 (Part 2) – 1981, Reaffirmed 2001.
  2. Code of Practice for Fire Safety of Buildings: Electrical Installations (Second Revision), IS 1646 – 1997, Reaffirmed 2002
  3. Indian Electricity Rules, 1956
  4. Central Electricity Authority (Measures Relating to Safety and Electric Supply) Regulations, 2010

  1. Clause 3.6.2 of IS 10028 Part 2 – 1981
  2. Clause, ibid
  3. Clause, ibid
  4. Clause 7.1 of IS 1646 – 1997
  5. Clause 7.4, ibid