450.13 Accessibility. All transformers and transformer vaults
shall be readily accessible to qualified personnel for inspection
and maintenance or shall meet the requirements of 450.13(A)
or 450.13(B).
(B) Hollow Space Installations. Dry-type transformers
600 volts, nominal, or less and not exceeding 50 kVA shall
be permitted in hollow spaces of buildings not permanently
closed in by structure, provided they meet the ventilation
requirements of 450.9 and separation from combustible materials requirements of 450.21(A). Transformers so installed shall not be required to be readily accessible.
Pete