30 CFR § 77.509 Transformers; installation and guarding.
(a) Transformers shall be of the totally enclosed type, or shall be
placed at least 8 feet above the ground, or installed in a transformer house,
or surrounded by a substantial fence at least 6 feet high and at least 3 feet
from any energized parts, casings, or wiring.
(b) Transformer stations shall be enclosed to prevent persons from
unintentionally or inadvertently contacting energized parts.
(c) Transformer enclosures shall be kept locked against unauthorized
entry.
