How to Select Terminal and Junction Boxes
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.
Related Products & Services
Electronic and Instrument Enclosures
Electronic and instrument enclosures are structures that house electronic components and instruments. They are usually designed for handheld or desktop applications. Example applications include calculators, cash registers, remote controls, and data acquisition instruments.
Industrial enclosures are used to house electronic components, equipment and devices. They are designed to protect personnel from accidental injury and to prevent the ingress of environmental contaminants.
Modular enclosures consist of smaller components that can be assembled to create custom enclosures, often for temporary or mobile systems. These modular components are available in standard sizes and allow modular enclosures to be used for a variety of purposes.
NEMA and IP Enclosures
NEMA and IP enclosures are designed to house electrical components, protect personnel from accidental injury, and prevent the ingress of environmental contaminants such as dust and water. NEMA enclosures are rated by the National Electrical Manufacturers Association (NEMA) and designed for hazardous or non-hazardous locations and indoor or outdoor use. Ingress protection (IP) enclosures provide protection against foreign objects and moisture.
Operator Interface Enclosures
Operator interface enclosures are used to house industrial controls such as display screens, pushbuttons, keyboards, lights, and other operator control devices. They are designed to protect personnel from accidental injury and to prevent the ingress of environmental contaminants such as dust and water.
Pushbutton enclosures are designed to house and protect electronic panels, controls, and components and while allowing functionality through pushbuttons on the surface. They are designed to protect personnel from accidental injury and to prevent the ingress of environmental contaminants such as dust and water.
Rack enclosures (rack cabinets, laboratory enclosures) are used to house standard 19 in. rack-mounted components or other standard-sized devices. They are designed to protect personnel from accidental injury and to prevent the ingress of environmental contaminants such as dust and water.
- Angled Front
- Carrying Handle
- DIN Rail Mounting
- EMI/RFI Coating
- Explosion Proof
- Explosion Resistant
- Flame Retardant
- Free Standing Cabinet
- Glue or Snap Together
- Grounding Strap
- Hinged Cover
- Open Frame Rack
- Rear Access Cover / Door
- RoHS Compliant
- Screw-on Cover
- Stainless Steel
- Type 0
- Type 0
- Type 1
- Type 1
- Type 12
- Type 12K
- Type 13
- Type 2
- Type 2
- Type 3
- Type 3