Schedule 40 is used for plumbing.

FWIW, the schedule number refers to a set of dimensional specifications, not the pressure rating. i.e. inside diameter, outside diameter and wall thickness, in order to ensure components of the same schedule will fit together.

DWV grade is for drain, waste and ventilation. There are also NSF and Pressure Rated grades for pressurized systems.

Indeed, Randy is correct. The "Schedule" refers to nothing more than the wall thickness. It doesn't imply a pressure rating or any other functional quality.

You can use Sched40 PVC conduit but as I stated in the other thread, it's functionality is quite limited as you can't use it to meet physical protection issues. If you just need something to contain non-cable individual conductors in places that aren't subject to physical damage, it's fine (and cheaper and lighter).

To clarify, if you are using conduit to run THHN, in a place that other wiring methods are acceptable (NM, MC, AC, SMURF..) then Schedule 40 is also acceptable. That is most interior wiring, although most people use EMT.

Other "required protection" is found in other articles, and is determined by locations and heights above grade or floor level...ranging from 6" to 8'.

300.5

(d) Protection from Damage.

Direct buried conductors and cables emerging from the ground shall be protected by enclosures or raceways extending from the minimum cover distance required by Section 300-5(a) below grade to a point at least 8 feet (2.44 m) above finished grade. In no case shall the protection be required to exceed 18 inches (457 mm) below finished grade.

Conductors entering a building shall be protected to the point of entrance.

Where the enclosure or raceway is subject to physical damage, the conductors shall be installed in rigid metal conduit, intermediate metal conduit, Schedule 80 rigid nonmetallic conduit, or equivalent.

334.15

(B) Protection from Physical Damage. Cable shall be protected from physical damage where necessary by rigid metal conduit, intermediate metal conduit, electrical metallic tubing, Schedule 80 PVC conduit, or other approved means. Where passing through a floor, the cable shall be enclosed in rigid metal conduit, intermediate metal conduit, electrical metallic tubing, Schedule 80 PVC conduit, or other approved means extending at least 150 mm (6 in.) above the floor.

(C)... NM cable installed on the wall of an unfinished basement shall be permitted to be installed in a listed conduit or tubing or shall be protected in accordance with 300.4 Conduit or tubing shall be provided with a suitable insulating bushing or adapter at the point the cable enters the raceway....

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320.23 In Accessible Attics.

(A) ... Where run across the top of floor joists, or within 2.1 m (7 ft) of floor or floor joists across the face of rafters or studding, in attics and roof spaces that are accessible, the cable shall be protected by substantial guard strips that are at least as high as the cable. Where this space is not accessible by permanent stairs or ladders, protection shall only be required within 1.8 m (6 ft) of the nearest edge of the scuttle hole or attic entrance.

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352.10

(F) Exposed. PVC conduit shall be permitted for exposed work. PVC conduit used exposed in areas of physical damage shall be identified for the use.

FPN: PVC Conduit, Type Schedule 80, is identified for areas of physical damage.

"in areas of physical damage" is fairly vague, and is subject to interpretation by the AHJ.