Performance Based Design

Transformer Exposure Analysis

Alternative means of compliance for minimum required standoff distance



The development of a 276-unit apartment building came to a halt when review of the site plan revealed a deficiency with a prescriptive code requirement contained within the National Electric Code. Site limitations had resulted in an arrangement where transformers were not positioned to maintain the required setback distances from both egress paths and adjacent structures. 


We performed fire modeling to demonstrate the proposed arrangement was consistent with the underlying objectives of the code while not explicitly adhering to the word of the prescriptive code. Through a holistic performance-based design analysis, we quantified likely fire scenarios and evaluated heat transfer from the transformer to the adjacent apartment building and egress paths. The fire modeling analysis led to a mutually acceptable solution between all parties that allowed the development to proceed.

Bottom Line

AHJ approved the transformer layout without drastic site plan modifications

65% decrease in the required separation distance (10 ft to 3.5 ft)

Services Provided

Performance Based Design


National Electric Code (NEC) Article 450.27

Factory Mutual Global (FMG) Data Sheet 5-4, Table 5

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