Terminal and Junction Boxes

Terminal and junction boxes are used to house electrical components and facilitate wiring. They are T-shaped or rectangular, made from a variety of materials, and available in many different sizes, sealing configurations and mounting styles. Length, width, and height are important dimensions. Inside length, inside width, and inside height are also important considerations. Because some terminal and junction boxes can be mounted in several different ways, suppliers recommend viewing product pictures or diagrams to determine which dimensions refers to length and which dimensions refer to width. For standard enclosures, the length or height is measured parallel to the hinge axis. For products with a screw-on or non-hinged cover, the length is the longer of the two dimensions. For enclosures that are rated by the National Electrical Manufacturers Association (NEMA), the width is perpendicular to the hinge axis and the depth is the distance from the opening to the back. 

NEMA ratings indicate whether terminal and 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. Types 1, 2, 12, 12K and 13 NEMA enclosures are rated for indoor use in non-hazardous locations. Types 3, 3R, 3S, 4, 4X, 5, 6, and 6P enclosures are rated for both indoor and outdoor use in non-hazardous locations. NFPA 70, a publication of the National Fire Protection Association (NFPA), is the basis of several NEMA ratings for hazardous locations. Type 7 and Type 8 NEMA enclosures are designed for Class I; Division 1; Groups A, B, C or D hazardous locations. Type 7 enclosures are rated for indoor use. Type 8 enclosures are rated for outdoor use. Type 9 NEMA enclosures are designed for indoor use in hazardous locations classified as Class II; Division 1; Groups E, F, or G. Type 10 NEMA enclosures are designed to meet the requirements of the Mine Safety and Health Administration (MSHA). Type 11 NEMA enclosures are designed for immersing the enclosed equipment in oil. 

The Ingress Protection (IP) ratings system from the International Electrotechnical Commission (IEC) describes the degree to which terminal and junction boxes provide protection against the ingress of foreign objects and moisture. There are six IP ratings for protection against foreign objects. Type 0 enclosures do not provide protection. Type 1 (>50 mm), Type 2 (>12 mm), Type 3 (>2.5 mm), and Type 4 (1 mm) enclosures provide protection against foreign objects of various sizes. Type 5 enclosures provide protection against dust. Type 6 enclosures are dust-tight. There are eight IP ratings for protection against moisture. Type 0 enclosures do not provide protection. Type 1 and Type 2 protect the enclosed equipment against dripping water. Terminal and junction boxes with Type 3 (spraying water), Type 4 (splashing water), Type 5 (water jets), Type 6 (heavy seas), Type 7 (immersion), and Type 8 (submersion) IP ratings are also available.

Selecting terminal and junction boxes requires an analysis of construction materials and mounting styles. Most products are made of aluminum, steel, stainless steel, fiberglass, plastic, polycarbonate, acrylonitrile-butadiene-styrene (ABS), or polystyrene. End panels are often made of clear, infrared, solid, or transparent plastic and include cutouts for DB9 or DB25 connectors. Some devices are designed to sit atop desks or mount in freestanding cabinets or open-frame racks. Others are wall-mounted or fit standard DIN rails. Specialized products are flame retardant, impact resistant, explosion proof, or shielded from electromagnetic interference (EMI) and radio frequency interference (RFI). Terminal and junction boxes with inner panels and multiple covers, doors, bays, and battery compartments are also available.

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