Electronic Enclosures

Electronic enclosures range in size from one square inch that fits a simple pushbutton assemblage to an entire room that contains large computer networks and wiring. Electronic enclosures are frequently rectangular and box-like; other styles are round or have sloping sides. Lids, removable panels, access points and vents are necessary in some applications, and recessed tops accommodate labels and keypads. Enclosures for handheld devices can have soft ergonomic grips and a battery door. Many enclosures simply snap together, although a tight seal to keep out dust and water is available using lap joint or tongue and groove construction. Not only do electronic enclosures protect their contents from pollutants or moisture, they also shield the internal equipment from electromagnetic interference, or EMI, that would disrupt the efficient performance of the circuitry inside the enclosure. Sometimes referred to as electrical cabinets, electronic enclosures are widely used in the medical, automotive and agricultural industries to protect equipment and instruments but can be found in any electronic application. Electrical enclosures can be custom made for a precise fit although there are already thousands of enclosure designs. Factors to consider when selecting an appropriate enclosure include size, construction materials, mounting, security and NEMA type, which refers to the grading assigned by the National Electrical Manufacturers Association.

Metals have traditionally been the electronic enclosure material of choice until the recent developments in plastics and composite materials. Aluminum enclosures are good thermal and electrical conductors. Though tough, aluminum is also malleable and very lightweight, especially when rolled into sheets. Stainless steel enclosures are also durable and corrosion resistant, having properties similar to aluminum. Many computer enclosures are made of aluminum or steel. Although electromagnetic interference can travel through these metals, they can be coated with a substance to screen their contents from the rays. For smaller and more complicated enclosures, moldable polycarbonate plastics are used. One similar material is acrylonitrile butadiene styrene, a common thermoplastic called ABS. Its superior electrical insulation properties and impact resistance make it a popular choice for electrical enclosures. Because it is lightweight and shock absorbent, ABS is used for pocket and handheld enclosures that will be handled frequently. Other types of enclosures include protective, desktop and mounted styles. Enclosures can be mounted by screws or fasteners that fit through the designated holes in the back or bottom of the housing.

Electrical enclosures are boxes that protect electronic equipment such as conduits, connections and switches from the environment and from tampering. They are found in public places such as street corners or parks as well as in buildings and residences. These rectangular enclosures are typically made from plastic or metal, particularly steel and aluminum, in order to resist corrosion and shelter their contents from weather and vandalism. Electrical cabinets can be horizontally or vertically oriented and usually bear a warning to alert those nearby to the sensitive and potentially dangerous equipment inside. They may also be locked. Some cabinets are mounted. Standardized rack mount enclosures accommodate multiple equipment modules that are 19 inches wide. Protruding edges allow the module to be fastened to the frame, which is usually steel or aluminum because of their strength and load-bearing properties. Professional audio equipment, computer servers and other electronics are stored inside the rack mount enclosure, and many models have a door that can be shut and locked. Depending on the application, the enclosure may use thicker metal for the frame and be encased in reinforced plastic, carbon fiber or Kevlar. Instrument enclosures can also be rugged; some are designed specifically for use in demanding situations where explosions, earthquakes or tornadoes may occur. These enclosures are often made from die cast iron or aluminum and range from small rectangular metal boxes to circular enclosures that can protect head-mount style instruments.

NEMA enclosures are certified by the National Electronic Manufacturers Association depending on the type of application for which they are used. They range from Type 1 to 13 and identify whether the enclosure is intended for indoor or outdoor use, in non-hazardous or dangerous situations and what it can protect from. Type 1, for example, is for general indoor use to prevent accidental contact with the enclosed equipment. Type 4X can be used indoors or outdoors and protects against corrosion, windblown dust and rain, sleet, snow, splashing or hose-directed water and the formation of ice on the enclosure. NEMA Type 12 is for industrial use indoors to protect from lint, dust, dirt, fibers, dripping, seepage and dripping non-corrosive liquids. The enclosure may not have any knockouts (partially punched holes) or openings except for oil and dust-tight mechanisms or gaskets. Hinged doors must require a tool to open and have an external means for mounting. By certifying enclosures, NEMA helps manufacturers and distributors get exactly what they need and ensures that the electronics inside will be able to function properly and safely.

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Electronic Enclosure Types

• Aluminum enclosures house and protect electronic instruments or equipment from damage or interference. Because these enclosures can be used indoors and outdoors, they must protect their contents from a variety of weather conditions as well as from dust and dirt.
• Computer enclosures are housings made specifically for computers. Computer enclosures are usually made of metal and are used to protect the inner electronics from dust and moisture damage.
  
• Custom enclosures are made to the detailed specifications of the customer. The sizes can vary to enclose a range of equipment, from a fuse box to a number of electronic devices and cables housed in a separate room, referred to as network racks.
  
• Double-shielded enclosures have an inner wall that is isolated from the outer wall with the exception of the region where the power-line filters and coaxial connectors penetrate. Double shielded enclosures can also be rooms.
  
• Electrical cabinets are filters designed to protect electronic parts from damage caused by dirt, oil, dust and moisture. These cabinets, used in virtually every industry, give electronic components a plane of operation that improves their efficiency.
• Electrical enclosures house electronic equipment and instruments from unintentional contact, contaminants and interference. The contents of these enclosures are often sensitive components of electrical circuits and need to be protected from dust, dirt, water and other liquids. Accidental contact could cause bodily harm and damage the equipment itself.
• EMI shielding involves using materials, such as filters, gaskets and coatings to block, absorb or redirect electromagnetic waves, in order to prevent electromagnetic interference (EMI) from harming sensitive equipment. These materials are attached to the metal surface of such enclosures.
• Instrument enclosures protect electronic devices inside a metal or plastic housing. Because of their sensitive circuitry, the components must be protected from dirt, water and accidental contact. Being kept in an enclosure prevents the intrusion of solid foreign objects as well as liquids to a certain extent.
• Junction boxes are a type of enclosure used specifically for wiring and the connecting of wiring to a larger unit and are often constructed with metal material. Junction boxes must have a cover plate and should be easily accessible.
  
• Metal boxes are metal enclosures that protect electronics.
• Metal enclosures are typically made of either aluminum or sheet metal. Metal enclosures are being replaced by enclosures made of lighter, more durable composites.
  
• NEMA enclosures are a specific type of electronic enclosure that is certified by the National Electronic Manufacturers Association (NEMA), which rates the enclosures bases on the type of application for which they are used. NEMA enclosures are typically made from carbon or stainless steel and can range in size from a pushbutton panel to a room-sized panel.
  
• Plastic enclosures are plastic housings that protect electronics.
• Pushbutton enclosures are either rectangular or wedge-shaped. Pushbutton enclosures have cutouts for surrounding and securing pushbuttons and can be mounted to a wall, pedestal or suspension system.
• Rack mount enclosures have standardized frames and racks for mounting multiple electronic equipment modules. Vertically stacked equipment saves floor space and is easier to maintain. The enclosures and modules are 19 inches wide, and the height is measured in multiples of 1.75 inches each called one rack unit (U).
• Stainless steel enclosures protect electronic equipment and instruments from damage due to interference, contaminants or accidental contact. Because of its corrosion resistance and lightweight strength, stainless steel is a popular material choice for enclosures, especially those that will be used in the food and beverage industry or in an setting with harsh chemicals.
• Terminal boxes are similar to junction boxes and are used for the housing and protection of a connection point between two different types of wire.

Electronic Enclosures Terms

Attenuation - A reduction in signal strength. Attenuation can occur naturally during normal signal transmission, or it may be produced intentionally by inserting a device in the path of the signal to reduce signal strength.

Bounding Surface - The outer surface of the electrical enclosure.

Cabinet - Often used interchangeably with either enclosure or rack. It is a piece of equipment designed to house or enclose something, such as electrical or process equipment.

Cable Glands - Seals that prevent water, dust, etc. from entering the enclosure at the point at which the cable is brought through the enclosure wall. Often, cable glands are installed via a gland plate.

EMI (Electromagnet Interference) Emission - The unintentional or undesired exiting of potentially interfering electromagnetic energy from electrical/electronic sources.

Flame Retardancy - The ability of a material to resist burning, sparking, sputtering or dripping when brought into contact with a naked flame. Not all enclosures are flame retardant.

Gear Tray - Also called a "mounting plate" or "mounting pan," it is a shelf that allows the mounting of equipment inside the enclosure. Gear trays are typically located at the rear of the enclosure, though some may be movable.

Gland Plate - Removable section of the enclosure, usually located on the bottom. The gland plate can be removed to allow the easy fitting of cable glands.

Permeability - The extent to which a material can be magnetized.

Plinth - Term used to describe various styles of mounting bases for floor-mounted enclosures.

Shielded Cables - Cables that have shields, such as braids or foils, to prevent EMI from entering or exiting the cable.

Rated Current - The input current of the equipment as declared by the manufacturer.

Shielding Vents - Vents that are used for HVAC or simple ventilation of shielded products, such as cabinets, rooms or enclosures. Some shielding vents also provide high shielding or air filtering.

Shielded Windows - Shielding consisting of a thin conductive film on the glass or a fine-wire mesh or metalized open-mesh textile.

Shielding Gasket - A material that maintains shielding effectiveness across a seam or gap in an electronic enclosure.

Type 1 - A NEMA rating indicating that the enclosures are intended for indoor, non-hazardous locations. Type 1 enclosures are mainly used to provide protection against limited amounts of falling dirt.

Type 3R - A NEMA rating indicating that the enclosures are intended for use in outdoor, non-hazardous locations. Type 3R enclosures are mainly used to provide protection against falling rain and external ice formation.

Type 4 - A NEMA rating indicating that the enclosures are intended for indoor or outdoor use in non-hazardous locations. Type 4 enclosures are mainly used to provide protection against splashing or hose-directed water, damage from external ice formation and windblown dust or rain.

Type 12 - A NEMA rating indicating that the enclosures are intended for indoor use in non-hazardous locations. Type 12 enclosures are mainly used to provide protection against dripping, non-corrosive liquids, circulating dust and falling dirt.