Underground metallic ducts not having an approved coating shall be encased in _________ inches of concrete.

Underground metallic ducts not having an approved coating shall be encased in _________ inches of concrete.

• A. 4
• B. 8
• C. 2
• D. 6

Answer: (C)

Ducts that run underground and lack any approved protective coating need a concrete barrier to shield them from moisture and soil, and to provide mechanical protection. The standard minimum thickness for this encasement is two inches of concrete, which gives effective protection without adding unnecessary cost or complexity. If the duct is coated or otherwise protected by an approved lining, the encasement requirement may be reduced or altered depending on the code, but for uncoated underground ducts, two inches is the specified minimum.

Ducts that run underground and lack any approved protective coating need a concrete barrier to shield them from moisture and soil, and to provide mechanical protection. The standard minimum thickness for this encasement is two inches of concrete, which gives effective protection without adding unnecessary cost or complexity. If the duct is coated or otherwise protected by an approved lining, the encasement requirement may be reduced or altered depending on the code, but for uncoated underground ducts, two inches is the specified minimum.