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 MIL-HDBK-1008B
d) Where transformers expose more than one building, such as
transformers located in courts or angles between buildings, or where yard
space is limited, they shall be enclosed in a suitable fire resistive vault
and protected as given in Table 3.2.3.2.1.
Table 3.2.3.2.1
Fire Protection for Oil-Insulated Transformers in Fire-Resistive
Vaults
SIZE (EACH TRANSFORMER)
NUMBER
PROTECTION
50,000 kVA and below
One or more not exceeding Hydrant
50,000 kVA total
Protection
50,000 kVA and below
More than one exceeding
Automatic
50,000 kVA total
Sprinkler or
water spray
systems
Over 50,000 kVA
One or more
Automatic
sprinkler or
water spray
systems
e) Where transformers are located on or above noncombustible
roofs, suitable curbed and drained concrete mats or welded steel pans shall be
underneath units and located so as to not expose roof structures. Oil-filled
transformers shall not be installed on combustible roofs.
Exception:
Existing carbon dioxide systems.
3.2.3.3
Indoor Oil-Insulated Transformers. Oil-insulated transformers
installed indoors shall be located in fire resistive vaults except for indoor
transformer installations exempted by NFPA 70. Fire protection shall be
provided in accordance with Table 3.2.3.2.1. Requirements apply to single-
phase or polyphase lighting or power transformers.
3.2.3.4
Less Flammable, Liquid-Filled Transformers. Transformers insulated
with less flammable liquids (fire point not less than 572 degrees F (300
degrees C)), as defined by ASTM D92, Standard Test Method for Flash and Fire
Points by Cleveland Open Cup, shall be permitted to be installed without a
vault in buildings of Type I and Type II construction in areas in which no
combustible materials are stored, where there is a liquid confinement area,
and where the installation complies with restrictions provided for in the
listing of the liquid. Such indoor installations not meeting the requirements
of the liquid listing, or installed in other than Type I or Type II buildings,
or in areas where combustibles materials are stored shall (1) be provided with
an automatic fire suppression system and a liquid containment area, or (2) be
installed in an approved vault. Transformers installed indoors and rated over
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