Terminal and Junction Boxes Information
Terminal and junction boxes are used to house electrical components and facilitate wiring.
When selecting terminal or junction boxes, correct size and adequate protection are the priorities. When considering quality of protection, material type and professional rating systems are the deciding factors. Additional features such as inner panels, doors, bays, and battery compartments can be important depending on the application.
Sizes and Shapes
The size and shape of a terminal or junction box depends on the design of the component or system being encapsulated. They are either rectangular or T-shaped, made from a variety of materials, and available in many different sizes, sealing configurations, and mounting styles. Enclosures may come in standardized dimensions or shapes which can be stacked for assembly, or they can be custom built to particular specifications.
The amount of protection and durability a terminal or junction box offers depends largely on its material composition. Most boxes are made from materials classified as either metals or polymers.
- Metals generally exhibit higher conductivity to both heat and electricity than other material types. Steel is widely used to form enclosures because of its strength and malleability. Stainless steel is used rather than standard steel in environments requiring corrosion resistance and lightweight materials. Aluminum is a less expensive, lightweight, and more conductive metal that exhibits good resistance to oxidation.
- Polymers are nonmetal materials with varying properties. ABS is a hard, rigid, inexpensive thermoplastic polymer that has good chemical and creep resistance, but is prone to cracking under stress. Fiberglass is a strong, durable, reinforced polymer that is resistant to many caustics and extreme temperatures. Polycarbonate exhibits excellent impact strength and can be molded to tight tolerances, but has only moderate resistance to chemical corrosion. Polystyrene is used for its rigidity, hardness, heat, and dimensional stability and because of its ease of fabrication.
End panels are often made of clear, infrared, solid, or transparent plastic and include cutouts for DB9 or DB25 connectors.
NEMA ratings indicate whether terminal or junction boxes are suitable for hazardous or non-hazardous locations and designed for indoor or outdoor use. All NEMA enclosures protect personnel against incidental contact with the enclosed equipment.
The Ingress Protection (IP) ratings system from the International Electrotechnical Commission (IEC) describes the degree to which terminal or junction boxes provide protection against the ingress of foreign objects and moisture. There are six IP ratings that describe protection against foreign objects and vary from >50mm particle protection to completely dust-tight protection. There are eight IP ratings for protection against moisture which vary from dripping water protection to protection when completely submersed.