N.Y.C. Admin. Code § 450.42: Section 450.42

Section 450.42 – Revise Section 450.42 to read as follows:

450.42 Walls, Roofs, and Floors. The vault shall be of such dimension as to permit the installation of all electrical equipment in accordance with 110.26 or 110.34 as applicable. The vault shall be of fireproof construction with a minimum fire resistance rating of 3 hours with floors, walls, and ceilings 6 in. (152 mm) thick if made of concrete, or 8 in. (203 mm) thick if made of brick, or 8 in. (203 mm) thick if made of filled cement block. All building steel forming part of the vault construction shall have a comparable fire resistance rating. Each compartment within a vault shall be built to the same specifications in respect to the thickness of walls and fireproof door, as the vault. The floors shall have approved structural strength for the load imposed thereon to be installed in the vault. The floors and walls, to the height of the sill, shall be given a hard impervious finish and painted to prevent the absorption of oil.

Exception: Where transformers are protected with automatic sprinkler, carbon dioxide, water spray, or approved gas suppression system, construction of 1-hour rating shall be permitted.

Informational Note No. 1: For additional information, see ANSI/ASTM E119-18a, Method for Fire Tests of Building Construction and Materials.

Informational Note No. 2: A typical 3-hour construction is 6 in. (150 mm) thick reinforced concrete.