Enclosure Basics
An electrical enclosure is a cabinet for electrical or electronic equipment. It is used to mount switches, knobs, and displays, while also preventing electrical shock to users and protecting the contents from the environment. Regulations may dictate enclosure features and performance in hazardous areas such as petrochemical plants or coal mines. Electronic packaging may demand heat dissipation, radio frequency interference protection, and electrostatic discharge protection, along with functional, aesthetic, and commercial considerations.
Electrical enclosures are typically made from rigid plastics or metals such as stainless steel, carbon steel, and aluminum. Some enclosures have knockouts (partially punched openings) for cables, connectors, or conduits. Small enclosures used mainly to conceal electrical junctions or protect them from tampering are often called junction boxes, street cabinets, or serving area interfaces.
NEMA Ratings
NEMA (National Electrical Manufacturers Association) uses a standard rating system that defines the environments in which an electrical enclosure can be used, and indicates its ability to withstand environmental conditions. Examples include:
- NEMA 1 & NEMA 12 – Rated for indoor use, protecting against solid objects, dust, and dirt.
- NEMA 4 – Protects against solid objects, water, and rust. Commonly used outdoors.
- NEMA 7 – Explosion-proof enclosures. Designed to contain explosions within the enclosure and prevent external hazards. Suitable for Class 1 Div. 1 and Class 1 Div. 2 environments.
There are many other NEMA ratings to help determine which enclosure is best for a given application. Beyond NEMA rating, consider the following when choosing an enclosure:
- Size – Account for the number of components and the space each requires.
- Back plate – Remember the mounting back plate reduces internal depth by 1–2 inches.
- Heat – Ensure the enclosure can dissipate heat generated by components.
- External obstacles – Consider nearby equipment, wiring paths, and externally mounted devices such as disconnects, HMIs, and push buttons.
- Material type – Choose the best material for the application. Options include steel, stainless steel, and various non-metallic enclosures.
By understanding the functions of electrical enclosures and asking a few key questions, we can ensure the proper enclosure is selected for each application.
