I have seen application where NEMA 13 enclosure mounted in the side of a pipe outside. OMG!!!

This article is meant to outline different classes of NEMA and what it means. I do not take credit for the content of this article as most of them are from other documents mentioned in the Reference section.

Lets get started…

The National Electrical Manufacturers Association (NEMA) is a US Manufacturers Organization which actively promotes standardized product specifications for electrical apparatus. While NEMA does not actually test products, it establishes the performance criteria for enclosures intended for specific environments. NEMA standards describe each type of enclosure in general and functional terms, and specifically omits reference to construction details. In other words, NEMA specifies what an enclosure must do, not how to manufacture it.

NEMA Classifications
NEMA 1
enclosures are typically used for protecting controls and terminations from objects and personnel. This style of
enclosure, while offering a latching door, does not have a gasketed sealing surface. NEMA 1 enclosures are used in applications where sealing out dust, oil, and water is not required.

NEMA 2
enclosures are intended for indoor use primarily to provide a degree of protection against limited amounts of falling water and dirt.

NEMA 3
enclosures are intended for outdoor use primarily to provide a degree of protection against windblown dust, rain,
sleet, and external ice formation.

NEMA 3R
enclosures are typically used in outdoor applications for wiring and junction boxes. This style of enclosure
provides protection against falling rain, sleet, snow, and external ice formation. Indoors they protect against dripping water. This style of enclosure does not have a gasketed sealing surface. Some models have hasps for padlocking.

NEMA 3S
enclosures are intended for outdoor use primarily to provide a degree of protection against windblown dust, rain,
sleet, and to provide for operation of external mechanisms when ice laden.

NEMA 4
enclosures are used in many applications where an occasional washdown occurs or where machine tool cutter coolant
is used. They also serve in applications where a pressurized stream of water will be used. NEMA 4 enclosures are gasketed and the door is clamped for maximum sealing.

NEMA 4X
enclosures are made of stainless steel, aluminum, fiberglass, or polycarbonate. NEMA 4X enclosures are used in harsh environments where corrosive materials and caustic cleaners are used. Applications include food, such as meat/poultry processing facilities, where total washdown with disinfectants occur repeatedly, and petro-chemical facilities, including offshore petroleum sites.

NEMA 5
enclosures are intended for indoor use primarily to provide a degree of protection against settling airborne dust, falling dirt, and dripping non-corrosive liquids.

NEMA 6
enclosures are intended for indoor or outdoor use primarily to provide a degree of protection against the entry of
water during occasional, temporary submersion at a limited depth.

NEMA 6P
enclosures are intended for indoor or outdoor use primarily to provide a degree of protection against the entry of
water during prolonged submersion at a limited depth.

NEMA 11
enclosures are intended for indoor use primarily to provide, by oil submersion, a degree of protection to enclosed
equipment against the corrosive effects of liquids and gases.

NEMA 12
enclosures are intended for indoor use to provide a degree of protection against drips, falling dirt, and dripping
non-corrosive liquids. NEMA 12 enclosures are most commonly used for indoor applications of automation control and electronic drives systems, including packaging, material handling, non-corrosive process control, and manufacturing applications. Gasketed doors seal the enclosure’s contents from airborne contaminants and non-pressurized water and oil.

NEMA 12K
enclosures with knock-outs are intended for indoor use primarily to provide a degree of protection against dust,
falling dirt, and dripping non-corrosive liquids other than at knock-outs.

NEMA 13
enclosures are intended for indoor use primarily to provide a degree of protection against dust, spraying of water,
oil, and non-corrosive coolant.

Reference

Reference
National Electrical Manufacturers Association
NEMA enclosure types
What Do The NEMA Ratings Mean?