This article provides comprehensive information about NEMA enclosures. You will learn how NEMA enclosures are made, and their materials of construction as well as applications, advantages, and drawbacks.
Read further to answer questions like:
NEMA enclosures are boxes that are designed to protect electrical components from the surrounding environment. Depending on the specific NEMA rating, devices in a NEMA enclosure are protected in:
While NEMA enclosures protect the enclosed equipment, they can also protect personnel and property in the surrounding environment:
NEMA enclosure ratings are based on the NEMA 250 standard issued by the National Electrical Manufacturers Association (NEMA), which is an organization that develops standards for end-users and manufacturers to improve the safety of electrical equipment.
NEMA enclosure standards are voluntary and self-certified by the enclosure manufacturer. Third-party certification is not required. The NEMA enclosure manufacturer agrees to manufacture to the standards.
Since you are counting on the supplier's promise that they have met or self-certified to the NEMA enclosure standards, you want to buy from a trusted, leading supplier.
Another option is third-party testing and certification. Several testing organizations will certify that the NEMA enclosures were made to NEMA standards such as Underwriters Laboratory, Intertek, and CSA.
A Certified NEMA enclosure provides additional assurance over a non-certified NEMA enclosure for critical applications. Government, military, and other customers may require certification on the enclosure used in your design or equipment.
NEMA enclosures have a rating system that determines the level of dust or liquids that can penetrate an enclosure or inversely, the level of protection that the enclosure will provide for the electronics that it contains. NEMA has created stringent testing and certification processes for each level of protection and NEMA enclosures will often require specific types of gaskets to help maintain the seal.
NEMA ratings define the level of protection that an enclosure provides against ingress to objects, particles, dirt, fine dust, water, water sprays or jets, and water immersion. Hazardous locations are defined in the National Fire NFPA 70®-2017, National Electrical Code®.
Besides, NEMA ratings are broken into three groups depending on whether enclosures are suitable for indoor, indoor, or outdoor, corrosive environments, and hazardous locations:
All NEMA enclosure types protect personnel against incidental contact with the enclosed equipment. Essentially, this protects an operator or user from being electrocuted.
NEMA enclosures are limited to electrical equipment operating at 1000 volts or lower.
A NEMA 1 enclosure is designed for general purpose indoor use only. Like all NEMA enclosures, they protect personnel against accidental contact with the enclosed equipment. NEMA type 1 enclosures protect the enclosed equipment from falling dirt.
A NEMA 2 enclosure is drip tight. They provide the same protection as a NEMA Type 1 enclosure, but also protect enclosed devices from dripping and light splashing of non-corrosive liquids. They typically have drip shields. They are employed where condensation can be severe such as in laundry rooms as well as near air conditioners, refrigerators, and other cooling equipment.
A NEMA 3 enclosure is weather-resistant. NEMA type 3 enclosures can be used indoors or outdoors. Like all NEMA enclosures, they protect personnel against accidental contact with the enclosed equipment. NEMA type 3 enclosures protect enclosed machines or devices from falling dirt, rain, sleet, snow, and windblown dust. NEMA Type 3 enclosures cannot be harmed by sleet or freezing rain forming an external ice layer on the enclosure.
A NEMA 3X enclosure has the addition of corrosive resistance compared to a NEMA 3 enclosure.
A NEMA 3R enclosure has all of the protective features of a NEMA type 3 enclosure except for no protection against wind-blown dust.
A NEMA 3RX enclosure has the addition of corrosive resistance compared to a NEMA 3R enclosure.
A NEMA 3S enclosure has all of the protective features of a NEMA type 3 enclosure with the additional benefit that any external mechanisms (handles, pushbuttons, etc.) remain operable even when ice-covered.
A NEMA 3SX enclosure has the addition of corrosive resistance compared to a NEMA 3S enclosure.
A NEMA 4 enclosure is watertight and can be hosed down. NEMA 4 enclosures can be used indoors or outdoors. They protect personnel against incidental contact with the enclosed equipment. NEMA type 4 enclosures are protected from falling dirt, rain, sleet, snow, windblown dust, splashing water, and hose-directed water. External ice formation will not damage NEMA 4 enclosures.
A NEMA 4X enclosure has the addition of corrosive resistance compared to a NEMA 4 enclosure.
A NEMA 5 enclosure is dust-tight. NEMA type 5 enclosures can be used indoors or outdoors. Like all NEMA enclosures, they protect personnel against accidental contact with the enclosed equipment. Personnel is protected against accidental contact with the enclosed equipment. NEMA 5 enclosures protect the enclosed equipment from falling dirt, settling airborne dust, lint, fibers, and flying debris as well as the dripping and light splashing of non-corrosive liquids.
A NEMA 6 enclosure is submersible. NEMA 6 enclosures are designed for indoor or outdoor use. Like all NEMA enclosures, they protect personnel against accidental contact with the enclosed equipment. NEMA 6 enclosures protect against the ingress of falling dirt as well as against the ingress of water from hose-directed spray and submersion of limited duration and depth. Like NEMA-type enclosures, they are not damaged by drips, sleet, or freezing rain forming an external ice layer on the enclosure.
A NEMA 6P enclosure can withstand prolonged submersion. Otherwise, they have the same protected capabilities as NEMA 6 enclosures.
A NEMA 7 enclosure is suitable for specific indoor hazardous locations. They are also known as indoor explosion proof enclosures. Like all NEMA enclosures, they protect personnel against accidental contact with the enclosed equipment.
The specific hazardous locations NEMA 7 enclosures can safely operate in are classified as Class I Groups A, B, C, and D in NFPA 70 standard of the National Electrical Code (NEC). Flammable chemicals in these classes include Acetylene, hydrogen, manufactured gas, Diethyl ether, ethylene, cyclopropane, gasoline, hexane, butane, naphtha, propane, acetone, toluene, and isoprene.
NEMA 7 enclosures are designed to contain an internal explosion without triggering an external hazard or explosion.
A NEMA 8 enclosure is suitable for specific indoor or outdoor hazardous locations. They are also known as indoor or outdoor explosion proof enclosures. Like all NEMA enclosures, they protect personnel against accidental contact with the enclosed equipment. The specific hazardous locations NEMA 8 enclosures can safely operate in are classified as Class I Groups A, B, C, and D in NFPA 70 standard of the National Electrical Code (NEC). Flammable chemicals in these classes include Acetylene, hydrogen, manufactured gas, Diethyl ether, ethylene, cyclopropane, gasoline, hexane, butane, naphtha, propane, acetone, toluene, and isoprene.
A NEMA 8 enclosure is designed to contain an internal explosion without triggering an external hazard or explosion.
NEMA 9 enclosures are dust-ignition proof. A NEMA 9 enclosure is suitable for specific indoor hazardous locations. Like all NEMA enclosures, they protect personnel against accidental contact with the enclosed equipment. The specific hazardous locations NEMA 9 enclosures can safely operate in are classified as Class II Groups E, F, and D in NFPA 70 standard of the National Electrical Code (NEC). Metal dust, carbon black, coal dust, and coke dust are the combustible powders in this class. A NEMA 8 enclosure immerses equipment in oil to prevent combustion. The design of NEMA 8 enclosures prevents the ignition of combustible dust.
A NEMA 10 enclosure is suitable for specific hazardous locations in mining applications. Like all NEMA enclosures, they protect personnel against accidental contact with the enclosed equipment. NEMA 10 enclosures meet the Code of Federal Regulations 30 Part 18 requirements of the Mine Safety and Health Administration (MSHA).
A NEMA 11 enclosure is suitable for specific corrosive environments. NEMA type 11 enclosures are drip-proof. They protect personnel against accidental contact with the enclosed equipment. The NEMA 11 rating may be obsolete or rare, but it is still referenced by suppliers. The addition of an X is used to designate NEMA enclosures with protection against corrosion.
NEMA 12 enclosures are general-purpose, indoor enclosures constructed without knockouts. A NEMA 12 enclosure is a slight step above a NEMA 11 enclosure in terms of protection ability.
They protect personnel against incidental contact with the enclosed equipment. NEMA 12 enclosures protect enclosed equipment against the ingress of solids, objects, and particles including falling dirt, circulating or airborne dust, lint, fibers, and flying debris. They also block the ingress general-purpose as dripping water and light splashing of non-corrosive liquids.
NEMA 12K enclosures are general-purpose, indoor enclosures constructed with knockouts. A NEMA 12K enclosure has all of the protective features of a NEMA 12 enclosure. The knock-outs are a welcome convenience when installing electrical wiring and cables.
NEMA 13 enclosures are general-purpose, indoor enclosures constructed with knockouts. NEMA 13 enclosures provide the same protection as NEMA type 12 enclosures with the addition of protection against splashing and spraying oils, lubricants, heat treat oils, greases, metalworking fluids, and coolants.
Underwriters Laboratories have their own standards for enclosures for the U.S. and Canada. UL ratings are for the U.S. and c-UL ratings are for Canada. Unlike NEMA ratings, manufacturers cannot self-certify.
Testing or certifying bodies such as UL, Intertek, and CSA can provide a listing certifying the NEMA enclosures meets the additional UL or c-UL standards. These third-party verified listings confirm the conformity of safety requirements and improve the quality of the enclosures
Underwriters Laboratory’s enclosure standards are:
The UL standards for enclosures are similar to NEMA 250 standard but limited in scope. They have no equivalent for NEMA type 3X, 3RX, and 3SX designations.
The applicable Canadian standards must be met to achieve a c-UL listing such as:
Intertek also provides listings or marks for enclosure products such as ETL, c-ETL, us-ETL. ETL. The ETL mark is recognized in the U.S. and Canada. ETL refers to “Electrical Testing Labs”, which was originally established in 1896 by Thomas Alva Edison.
The International Electrotechnical Commission (IEC) issues similar ingress protection (IP) ratings for enclosures. In industrial applications in the U.S. and Canada, NEMA rated enclosures seem to be predominant. Cameras, smartphones, and other consumer products tend to be IP rated.
-ratings.jpg "IEC Ingress Protection (IP) Ratings")
The IEC IP rating system is more limited or less inclusive compared to the NEMA rating system for enclosures.
A specific NEMA rating can meet or exceed a specific IEC IP rating, but the two systems are not equivalent.
IEC IP ratings are only concerned with dust, object, and water ingress. Whereas, NEMA ratings take into consideration additional factors such as icing; corrosion resistance; oil, lubricant and coolant resistance, and specific construction details.
NEMA ratings only apply to completely built and installed enclosures. IP ratings can apply to a partially complete enclosure installation.
What I find interesting when comparing NEMA and IP rating systems, is the lack of IP rating types for hazardous locations.
IECEx and ATEX ratings for hazardous locations. The International Electrotechnical Commission established the IECEx certification system to internationally assure safety compliance of equipment and enclosures used in hazardous locations. IECEx is based on the IEC 60079 standard for enclosures hazardous areas.
ATEX certifications are based on European Union (EU) standards, the EU ATEX Directive. They are only applicable for enclosures or equipment sold and used in the European Union. ATEX designations define requirements of safe enclosures for hazardous areas containing flammable liquids, vapors, gases, or combustible clouds of dust. ATEX certification applies to electrical and mechanical equipment used on the surface, below the ground, and on fixed offshore installations.
Industrial settings can have high levels of electromagnetic or radio frequency interference (EMI or RFI) from motors, induction heaters, electromagnets, RF transmitters, fluorescent lighting, halogen ballasts, arc welders, microwave ovens, RF generators, or other electrical equipment.
EMI/RFI shielding is used to block emissions or signal leaks from within a shielded enclosure as well as prevent external EMI/RFI from disturbing sensitive instruments and electronics within a shielded enclosure.
There are a variety of different standards and organizations provide schemes to designate or rate shielding for electromagnetic and radio frequency interference:
An electrically conductive or magnetic layer is required to shield electronics and electrical equipment from EMI and RFI. A plastic enclosure requires a metallic coating to shield its contents. A metal enclosure should inherently provide shielding. A ferromagnetic metal such as carbon steel or a 400 series ferritic stainless steel can shield magnetic fields as well as electrical fields.
EM/RF interference can still leak through gaskets on metal and metalized plastic enclosures. A shielding gasket maintains shielding effectiveness across a seam or gap in a shielded NEMA enclosure between covers or doors and the enclosure. Shielding gaskets consist of metalized polymers (silver-coated nylon), metal foil-polymers, conductive fabric-wrapped foam, wire mesh, stamped metals, and expanded metal.
The Telcordia GR-63 CORE Network Equipment Building Seismic Standard is typically applied to determine the suitability of NEMA enclosures for seismic duty. The standard divides the U.S. up into zones with varying levels of earthquake risk. Zone 4 (California, Alaska) has high risk while Zone 0 (Wisconsin, Florida) has low risk.
Data and communications equipment are especially sensitive to seismic disturbance. The NEBS rating is employed most often with NEMA rack enclosures, NEMA rack cabinets, and open frame racks.
For markets outside the U.S., the International Building Code (IBC) formerly known as the Uniform Building Code (UBC) standards also has a “High Seismic Areas” standard. The IBC/UBC standards are less stringent and more component-focused than the U.S. standard.
RoHS and REACH restrict the use of certain toxic or hazardous substances in electrical and electronic equipment.
Restriction of Hazardous Substances (RoHS) does not allow the use of the following ten materials and chemicals in electrical and electronic devices sold in the EU:
The European Union’s REACH Directive is applied to all materials, solvents, paints, chemicals, and other substances used in the manufacture of electrical and electronic equipment. The goal of REACH is to reduce exposure to carcinogens, mutagens, toxins, and other dangers. Suppliers are required to provide information on chemicals related to the health and safety impact of the products supplied.
In addition to the NEMA type number, NEMA enclosures can be classified three ways:
Some enclosures are mounted to a machine or a wall in a factory while other NEMA enclosures are freestanding or floor mounted. The NEMA enclosure is engineered with the required mounting flanges, legs, mounting holes, or mounting brackets for the mounting location.
Mounting kits might be included with the NEMA enclosure or sold as an add-on option or accessories. Mounting kits include leg kits, pole mounting kits, pedestals and pedestal mounting kits, fastener kits, and mounting bracket kits.
Desktop NEMA enclosures are designed to be mounted on workbenches, tables, and desktops. Analytical instruments might be housed in a desktop NEMA enclosure to enable an analysis of chemical compositions while protecting the instrumentation electronics and detectors from the wet and corrosive environments found in industrial, R&D, and quality control laboratories.
DIN rail systems are commonly used to mount sensors, controllers, relays, switches, and other monitoring and control components. A DIN rail NEMA enclosure is designed to be mounted on a DIN rail and protect sensors, electronics, and electrical devices sensitive to the conditions in the plant environment. DIN is the German standards organization or the German equivalent to ANSI, the U.S. national standards body.
Drop over NEMA enclosures have lifting eyes and an open bottom. The drop over enclosure is lifted by the eyes and positioned over the larger types of electrical equipment requiring environmental protection. Motor control centers, drives, transformers, and electrical metering units, and electrical distribution systems are often protected with a drop over enclosure. Walk-in, ground, and pad type enclosures can often be drop over enclosures.
Floor mount NEMA enclosures are not much different than free standing NEMA enclosures, but they are bolted or attached to the floor. Floor mounted enclosures can be less deep compared to free standing NEMA enclosures.
They typically employ unibody construction and are used in stand-alone applications versus integration into a machine or system. They can be heavy and often have eyes on the top to allow lifting and placement without damage to the sheet metal and internal devices.
Floor mounted enclosures usually have floor supports or legs and are elevated off the floor to provide easier cable access. Most floor mounted panels are wide with a wide back panel for mounting instruments, monitoring electronics, and industrial controls. These larger NEMA enclosures usually have lifting eyes for easy placement or removal.
Free Standing NEMA enclosures rest directly on the floor and are not bolted or anchored to the floor. Free standing NEMA enclosures are typically formed as a single monolithic or unibody enclosure. However, at least one supplier provides modular free-standing enclosures. Free standing enclosures are often used in stand-alone enclosure applications.
Free standing enclosures do not have legs, floor supports, or a floor support kit. They typically have a deeper base down inside the enclosure door, which prevents the door from scraping the floor. The width and front-to-back depth of free standing NEMA enclosures are typically greater to provide higher stability - so they don’t tip over.
They tend to be very heavy and often have eyes on the top to allow lifting and placement without damage to the sheet metal and internal devices.
Free standing enclosures, single or double front doors and an optional rear door or removable rear panel. They usually contain internal back and side panels for mounting automation devices, PLCs, drives, contactors, relays, controllers, IT equipment, or process instrumentation. Some free-standing NEMA enclosures utilize DIN rails, 19” EIA rack rails, fixed frames, or swing-out frames for mounting devices.
Handheld NEMA enclosures integrated with pushbutton switches or joystick controllers and used to activate a winch, hydraulic press, or train a robot arm. Handheld NEMA enclosures are smaller and typically have a rectangular or T-shape.
Ground or pad-mounted NEMA enclosures are large NEMA enclosures mounted on a concrete pad. They are typically found in outdoor applications. They often have an open bottom where wiring or cable feeds up through. Ground-mounted enclosures house industrial controls, motor drives, power distribution equipment, and transformers.
Pole-mounted NEMA enclosures are designed for outdoor mounting on a pole such as electrical distribution line poles. They can contain electrical, network, and communications equipment. Tower-mounted NEMA enclosures fall into this category.
Pedestal-mounted NEMA enclosures are designed for mounting on a pedestal where the pedestal is securely anchored to the floor. Operator interfaces and machine control are often mounted on pedestals. Cabling runs from the pedestal NEMA enclosure down through the pedestal, through a trough enclosure or protective jacket, and then finally to the machine tool, press, or process equipment. Pedestal enclosures are not the same as pedestal-mounted enclosures. A pedestal enclosure is a type of outdoor enclosure for utility applications.
Rack-mounted NEMA enclosures are designed to fit into 19 inch EIA racks or 24-inch racks. They may have integral or optional pull handles and rack mounting brackets. Some rack-mounted NEMA enclosures are also utilized as desktop NEMA enclosures.
Walk-in NEMA enclosures are extremely large NEMA enclosures with one or two doors. They often have an open bottom, but they can have a full floor. They are very heavy and usually have lifting eyes to position over a pad. They can protect switchboards, switchgear, transformers, drives, industrial controls, and other power distribution equipment, which is too large for small pad-mounted enclosures or cabinets.
Wall-mounted NEMA enclosures are bolted or attached to a wall or vertical surface and come with molded or welded brackets to ensure easy mounting. They can contain 19 inch EIA rails or back panels for automation components.
Wall-mounted enclosures are suitable for smaller electrical devices, instruments, and controllers. They can not hold as much equipment as floor mounted and free standing NEMA enclosures.
Wall-mount enclosures are available in two variations:
NEMA control panel enclosures protect control panel components such as push button switches, monitoring devices, controllers, membrane switch panels, alarms, annunciators, indicator lights, tamper sensors, and other control equipment. Specialized NEMA control panels include:
NEMA battery enclosures are designed to contain standard battery sizes in outdoor, marine, highway, and factory locations exposed to dust, snow, rain, or water. They can contain leaks from acid batteries. They are often used in conjunction with a solar power system to provide power during the night.
Commercial NEMA enclosures are designed for applications in stadiums, theaters, retail stores, malls, office building complexes, and other commercial sites. They may house the controls for elevators, escalators, HVAC systems, and electrical power systems.
Data center enclosures, IT and telecommunication cabinets, fiber optic termination boxes, and network boxes can be constructed using a NEMA enclosure. They can contain patch panels, network switches, servers, and uninterruptible power suppliers (UPS).
Console and console enclosures often have an angled back front panel with two trapezoidal side panels. They can be floor, pedestal, and desktop mounted.
Consoles and consolets are typically used to protect controllers, instrumentation, and industrial computers, which are controlling a machine or process equipment.
Console and console type enclosures include pushbutton consolets, workstations, and operator consoles. Industrial computer enclosures and kiosk enclosures are application specific types of console enclosures.
Electrical disconnect NEMA enclosures are designed to contain disconnect switches, load break switches, and circuit breakers. Electrical disconnects are used to completely de-energize an electrical circuit before any maintenance of equipment or electrical distribution systems is performed.
Drive enclosures and motor control central enclosures house motor drives, inverters, and motor controllers, which provide the required electrical power to control the speed and operation of AC or DC motors. Drop-over drive enclosures are used on larger installations.
NEMA enclosures suitable for hazardous locations containing volatile or combustible gases or substances are designed to suppress internal explosion and prevent the internal explosion from triggering an external explosion.
NEMA enclosures are also utilized in hydraulic and pneumatic controls. Fluid power controls can activate and deactivate cylinders, hydraulic motors, and fluid power valves. The NEMA control panel may contain electropneumatic and electrohydraulic elements as well as electrical switches and control panel indicator lights.
Pressurization and purging equipment and systems found in process plants are also housed in NEMA enclosures.
Industrial grade NEMA enclosures are suitable for manufacturing factory and process plant settings. They tend to be made of cold rolled steel, galvanized steel, stainless steel, and aluminum usually in heavier gauge thickness to provide a durable enclosure.
NEMA instrument enclosures are used to protect instrumentation such as monitors, analyzers, and data loggers in factory settings. The instruments may measure temperature, pressure, humidity, flow, part count, force, strain, and other process or manufacturing parameters. Instrument enclosures tend to be smaller housings, but larger NEMA instrument enclosures are available for complex processes requiring extensive measurement and data logging.
Junction box NEMA enclosures protect wiring connections, DIN rail, or terminal wiring in an electrical distribution system. They may also contain switches and outlets or receptacles. Junction boxes are also known as terminal boxes and utility boxes.
NEMA message board or display enclosures protect display screens placed in overhead factory locations to alert operators, technicians, and engineers process conditions, productivity levels, and hazardous situations. Vorne systems are commonly displayed on message boards housed in a NEMA enclosure.
Metering cabinets house transformers and electrical metering equipment and are often located outdoors with exposure to rain, snow, and ice, where a NEMA rated cabinet type enclosure is required. They are also known as utility measurement cabinets.
Miniature NEMA cases are smaller NEMA enclosures commonly used to house smaller sensors, transducers, sensor transmitters, instruments, printed circuit boards, and other electrical and electronic devices.
A miniature NEMA case can be integrated into or part of a product design. They may form the housing or case of a handheld instrument or monitor, which has to operate in dusty, wet, or hazardous locations. A miniature case is similar to or a smaller version of an instrument enclosure.
Enclosure designed to contain operator interface devices such as electronics, controls, pushbuttons, joysticks, switches, membrane switch panels, and displays.
Operator interface equipment allows an operator to monitor and control manufacturing equipment, machinery, and process equipment in plant settings. Human-machine interface (HMI) devices are similar products used to interact with machines and processes.
Console enclosures, console enclosures, pushbutton enclosures, PC enclosures, and handheld enclosures can be considered types of operator interface NEMA enclosures.
NEMA PC enclosures house and protect industrial computers, industrial computer boards, monitors, keyboards, and peripherals. They are typically employed for process and machine control.
Pushbutton NEMA enclosures have front panels with an array of holes to accommodate push button switches. Additional custom gaskets or seals are required to seal these openings.
NEMA Rack enclosures contain 19 inch EIA rails for mounting standard network and communications equipment such as servers, routers, UPS systems, network switches, audio-video equipment. Rack enclosures are also found in cleanroom and laboratory environments.
Hygienic or sanitary NEMA enclosures are designed for applications in food & beverage, pharmaceutical, hospitals, dental, and medical device manufacturing industries where the ability to washdown to maintain clean and disinfectant equipment is critically important. Sanitary NEMA enclosures typically are constructed from stainless steel and have removable seals for thorough cleaning and disinfection. NEMA type 4 or 4X watertight enclosures suitable for washdown with high-pressure water would be a good choice.
Solar energy NEMA enclosures contain wiring, wiring terminals, batteries, and charge controllers. Batteries are sometimes housed in a separate NEMA battery enclosure.
Traffic control NEMA enclosures protect rail, mass transit, and street signal and flashing light controls such as timing clocks, lightning arrestors, circuit breakers, disconnect switches.
NEMA tamper and vandal proof enclosures have locks or lockable latches to prevent tampering by vandals or unauthorized personnel. They may also have a tamper sensor to detect when a control or security panel enclosure is opened without disarming the system first.
NEMA wireways and wiring trough enclosures organize cables and wiring. They can protect wiring runs from dirt, dust, oil, dripping water, rain, sleet, and snow.
They are like ductwork for wires and cables. They are made in different shapes. In addition to straight sections, several connectors or adapter ways or troughs are available such as:
Wireways can be considered a type of raceway or enclosed conduit. Wiring troughs are typically supplied with two end caps or closed ends, while wireways have open flanged ends. Wiring troughs can have knockouts along the sides or on the closed ends.
Wireways are available in three types:
Wireways and wiring troughs are also known as conduits, gutters, raceways, wiring ducts, and wire ducts.
Modular enclosures tend to be designed around a frame where the side, front, top, bottom, and back panels attach to the frame. The external panels can be manufactured from sheet metal, extrusions, and roll formed parts. The frame is mounted to the floor with leveling feet on the frame or a base plinth.
The modular nature enables enclosure manufacturers, system integrators, OEMs, and manufacturing facilities more flexibility in designing and building configurations and modifications tailored to specific applications.
Modular enclosures are commonly used like information technology (IT) equipment cabinets with 19" EIA mounting rails for IT components. Internal side and back panels are used to mount automation equipment such as monitors, relays, data acquisition units, and controllers.
Monolithic or unibody enclosures consist of a single solid structure such as formed sheets welded together, molded fiberglass, or diecast aluminum. In large enclosures, the monolithic or unibody construction can provide better structural load support compared to a modular or bolted assembly. Customization and modification may not be as easily implemented compared to modular enclosures.
The amount of protection and durability an enclosure offers depends largely on its material composition. Most enclosures are made from materials classified as either metals or polymers. Typical materials are coated steel, galvanized steel, stainless steel, aluminum, fiberglass, and plastic.
Metals generally exhibit higher conductivity to both heat and electricity than other material types. The electrical conductivity is useful in grounding the box.
Metal enclosures can shield enclosed electronics and electrical devices from electrical and magnetic fields or electromagnetic interference (EMI) and radio frequency interference (RFI). Noise can still be transmitted through gaps in doors and openings for signal and power supply lines.
Common NEMA enclosure shapes are rectangular and square boxes. Less common shapes are round boxes, T-shape enclosures, and angled front boxes. T-shaped enclosures have a lower handle attached to a square or rectangular box.
The basic parts of an enclosure include the enclosure box, enclosure cover, enclosure bezel, enclosure legs or stand, and mounting devices.
Steel, aluminum, stainless steel, and other metallic NEMA enclosures and enclosure parts can be made by bending, forming, drawing, roll forming, and stamping sheet metal in the required shapes.
Aluminum sheet metal is easier to fabricate into a box or enclosure shape because the metal has high ductility and high formability. While aluminum sheet metal can be easily formed, aluminum enclosures are also manufactured via die casting and extrusion.
Aluminum is softer than steel and easier cut or machine. Aluminum is so soft even woodworking carbide saw blades can cut it.
Steel is widely used to form enclosures because of its strength and malleability. Steel is a commercial iron alloy that contains carbon. Low carbon steels such as 1020 or 1010 are softer and easy to form. Steel or stainless steel has far more impact resistance compared to plastic.
In a busy, factory environment, a heavy-walled coated steel or stainless steel enclosure will withstand denting and impacts better than aluminum or plastic enclosures. While a fork truck might dent a steel enclosure, the same impact will likely smash a fiberglass or plastic enclosure into pieces.
Steel does not have the inherent corrosion resistance compared to plastics and stainless steels. A steel enclosure will require an additional protective coating such as electroplating, zinc galvanization, or powder coating. Coatings can be selected to provide or match the colors needed for new products under development as well as older equipment being refurbished.
Stainless steel is used rather than standard steel in environments requiring corrosion resistance. Stainless steel is chemical and corrosion-resistant and can have relatively high-pressure ratings.
304 and 316 austenitic stainless steels are the most common and corrosion resistant grades for enclosures. 316 stainless has better pitting corrosion resistance in chloride and saltwater environments. 304L and 316L stainless steels are low carbon versions designed to maintain corrosion resistance after welding.
400 series ferritic stainless steels are used in some applications such as shielded NEMA cabinets for telecommunications and IT. 400 series ferritic stainless steels are magnetic and very formable, but not as corrosion resistant as 300 series stainless steels.
While stainless steel is more costly than aluminum or steel, stainless steel is essentially maintenance-free because a coating does not need to be stripped and reapplied during service. In fact, a coating on stainless steel is detrimental to corrosion resistance performance and should not be applied to stainless steel enclosures.
Aluminum is more expensive than steel, but some of aluminum’s properties are superior to steel. Aluminum is lightweight or lower in density compared to steel or stainless steel, so the lighter weight might be a selection factor for an enclosure for airplanes, spacecraft, or vehicles.
Aluminum has higher electrical and thermal conductivity compared to steel. The higher thermal conductivity can help in the thermal management or heat dissipation from the joule heating of the enclosed electrical or electronic components. Aluminum fins can be extruded during the manufacture of aluminum enclosures to further enhance heat removal from the enclosure.
Aluminum has better oxidation resistance compared to steel, but still requires anodizing or protective coatings in corrosive environments such as ocean salt sprays or chemical plants.
A 316 stainless enclosure can cost almost twice as much as a coated steel enclosure of the same size. 316 stainless steel should only be specified in industrial environments where the added corrosion resistance is required. 304 stainless steel will cost about 50% more than a coated steel enclosure. While aluminum costs more per pound than steel, aluminum’s density (2.7 g/cm3) is only 34% of steel’s density (7.8 g/cm3). As a result, aluminum will only have a 20% premium over coated steel. The costs were derived from listed prices on a leading suppliers website.
Plastic or fiberglass NEMA enclosures are typically manufactured using a molding process. Thermoplastic resin enclosures can be injection molded, extruded, and thermoformed. Common thermoplastic enclosure materials include PVC, ABS, and polycarbonate resins.
Plastics and fiberglass can be machined without difficulty to produce cutouts or openings for wiring, switches, and operator interface controls.
The fiberglass fabrication process will vary depending on the glass fiber product used. Fiberglass materials can be in the form of short or long glass fibers, a nonwoven glass matt, or a woven fiberglass cloth.
Thermoset resin-based fiberglass enclosures can be made from sheet molding compounds (SMCs) or bulk molding compounds (BMCs) are usually compression or injection compression molded. Reaction injection molding (RIM) can also mold certain thermoset resins such as polyurethanes into enclosures.
Resin transfer molding (RTM) is also used for molding thermoset fiberglass enclosures. Fiberglass matt or woven fabric is placed or laid up in a mold, thermoset resin for the matrix is mixed with a hardener or catalyst, and then resin is transferred or injected into the mold.
The SCRIMP (Seemann Composites Resin Infusion Molding Process) is an RTM process that uses a vacuum to pull liquid resin into a mold containing the fiberglass reinforcement. SCRIMP can repeatably make high-quality fiberglass parts with minimal VOC emissions.
Large custom enclosures or even industrial shelters are fabricated with manual lay-up molding. In the manual lay-up process, fiberglass cloth or nonwoven mats are laid into a mold. Thermosets are poured or sprayed onto the fiberglass. Rollers and squeegees are used to “wet out” the fiberglass or force the resin into the fibers, remove trapped air, and wipe away excess resin.
Pultrusion processes can be used to make long channel shapes or ribs in larger sheets. A long channel shape might be useful for fabricating a NEMA wireway enclosure. Pultruded plastics are reinforced with long strands of fiberglass in a continuous extrusion-like process.
Plastic and fiberglass enclosures can be pigmented to match a specific color of a product assembly under design or older equipment being refurbished. Coatings can also be applied to plastic and fiberglass enclosures to enhance environmental resistance, improve UV and weatherability, and provide specific colors for an application.
Polymer-based materials such as plastic or fiberglass are nonmetal materials with varying properties depending on the specific fillers, reinforcements, and additives employed in the compounding formulation. Common trade names include Cycolac® (GE Plastics), Lustran® (Bayer), and Novodur® (Bayer).
Acrylonitrile-butadiene-styrene (ABS) is a hard, rigid, inexpensive thermoplastic terpolymer that has good chemical resistance and dimensional stability.
ABS develops good impact resistance through a “rubber toughened” structure where fine rubbery butadiene spheres are dispersed in a rigid plastic matrix. Hard hats, automotive bumpers, and golf club heads are often made from impact-resistant ABS.
Fiberglass or fiberglass reinforced plastic (FRP) is a strong, durable, reinforced polymer that is resistant to many caustics and higher temperatures compared to plastics. However, fiberglass is not immune to an environmental attack. Over time yellowing, discoloration, gloss reduction, fiberglass bloom, and blistering can occur on fiberglass enclosures.
Fiberglass can have less shrinkage during molding and better dimensional stability compared to certain molded plastics.
Fiberglass is a plastic composite with reinforcing glass fibers. The glass fiber product used can be in the form of short or long glass fibers, a nonwoven glass matt, or a woven fiberglass cloth.
The most popular fiberglass thermoset resins include polyester and epoxy.
Polycarbonate (PC) is an amorphous material with excellent impact strength, clarity, and optical properties. Common brand names include Caliber® (Dow), Lexan® (SABIC), Makrofol®, and Makrolon® (Bayer). Clear polycarbonate windows have 200 times the impact strength of glass windows.
Polycarbonate is very tough and has excellent mechanical properties. PC can be molded to tight tolerances. Polycarbonate can be attacked by solvents and certain chemicals. The weatherability of polycarbonate is only fair but can be enhanced with additional UV inhibitors and protective coatings.
Polypropylene is a thermoplastic with excellent resistance to many chemicals, which explains the wide use of this material for chemical laboratory bottles and labware. Enclosure covers, bezels, small junction boxes, and handheld enclosures are sometimes fabricated from polypropylene resins.
Polystyrene is a low-cost thermoplastic, which tends to be more brittle compared to tougher polymers such as polycarbonate or polyamides (Nylon). Enclosure covers, bezels, small junction boxes, and handheld enclosures are sometimes fabricated from polystyrene resins
Polyvinyl chloride (PVC) is a relatively inexpensive and chemically resistant thermoplastic. PVC is not as tough as polycarbonate. PVC and modified PVC, CPVC, are commonly used in plumbing applications. Enclosure covers, bezels, small junction boxes, and handheld enclosures are sometimes fabricated from PVC resins.
The enclosure components are assembled and joined with fasteners, welds, and less commonly adhesives. A fastened enclosure assembly would be considered a modular enclosure. Modular enclosures can be more easily customized by mixing and matching modular components.
Fasteners allow disassembly for repair or part replacement, but the fastened parts can loosen under vibration or shaking found in industrial settings. Additional sealing washers might be required depending on the specific NEMA or IP rating of the enclosure.
Welded enclosure components cannot loosen during operation when exposed to vibration or motion. Leak tight welds on a welded enclosure can eliminate the need for additional seals, gaskets, or sealants on a NEMA enclosure.
A monolithic or unibody enclosure is constructed of a single, solid piece of metal or plastic using aluminum die casting, plastic injection molding, or welding of formed sheet metal parts into a single structure. Repair or replacement of a damaged component in a welded assembly can be more troublesome. The monolithic or unibody NEMA enclosure can be sturdier and have fewer gasketed gaps and therefore lower chance of ingress.
While a NEMA enclosure may seem like a simple metal or plastic box, every NEMA enclosure can be customized with specific panel cutouts, coatings, and accessory parts. Customization of metal NEMA enclosures requires less tooling investment, which has to be considered in comparison to plastic NEMA enclosures.
Specialized custom coating and printing can be applied to enhance a NEMA enclosure for specific designs and applications.
Openings need to be made into a NEMA enclosure to provide electrical power for housed devices. Data signals need to be transmitted to and from electronic devices, monitors, process controllers, data acquisition modules, and controllers inside the NEMA enclosure.
Power cabling from motor drives, contactors, transformers, and relays must pass through the NEMA enclosure walls to the motors, heaters, pumps, machine tools, lasers, or other manufacturing equipment being monitored and controlled.
The openings in the NEMA enclosures have a variety of configurations:
NEMA enclosures have doors and covers, which work with a seal or gaskets to prevent ingress of dust or water. A variety of different covers and doors are available from leading manufacturers:
The gaskets and seals utilized in a NEMA enclosure are a critical component in delivering protection against water, oil, dust, dirt ingress. The three main types of gaskets or seals include:
NEMA enclosures can contain additional components for the internal mounting of electronics and electrical equipment. Components for mounting device inside the NEMA enclosure include:
NEMA enclosure may benefit from thermal management to maintain the temperatures in the enclosure in a range where electronics and electrical components can function properly.
A NEMA enclosure can be designed to allow enclosed devices to operate efficiently in a frigid cold, outdoor setting. The NEMA enclosed can be encased in ice in some cases. Insulation or an internal heater might be beneficial in low-temperature applications.
Investment metal casting foundries, forges, heat treating operations, glass melting furnaces, primary metal furnaces, and oil refineries can create elevated temperature environments. Drives, transformers, and process controllers in NEMA enclosures may require fans, air conditioning, or other coolers to maintain instrumentation within allowable operating ranges.
Some thermal management accessories or options can include:
Additional enclosure parts include:
You should realize by now that the NEMA rating number is the main specification when ordering a NEMA enclosure.
The dimensions and shape are also key specifications when ordering a NEMA enclosure. The enclosure size and shape depend on the size and shape of the electrical or electronic device to be protected by the NEMA enclosure. The NEMA enclosure should be large enough so the devices can be repaired in-place or removed for repair.
Enough clearance between the electrical devices and the walls of a metal NEMA enclosure should be present to route in wiring while avoiding electrical shorts or ground faults to the enclosure housing.
Another sizing factor is the amount of room available for the enclosure in the facility, on a machine tool, or within a piece of process equipment.
A key factor that has to be considered when ordering a NEMA enclosure is any alterations that may be made to the enclosure during installation or purchase such as adding holes or altering the position of the door nullifies the enclosures NEMA rating
NEMA enclosures typically have rectangular box shapes, but they can be custom-made in many different shapes and with many additional features.
Manufacturers will often have a catalog of standard shapes and sizes, but they can make custom shapes and sizes for specialized applications with sufficient order volumes.
Like any engineer, I tend to gravitate toward standard or catalog parts. In the back of my mind, I believe a catalog part will cost less than a custom part.
In theory, catalog, standard, and COTS parts can be ready to order and do not require any additional engineering.
However, you should look at or perform a total cost-benefit analysis for using a standard versus custom part.
In any case, most catalog NEMA enclosures will require some degree of customization or configuration for industrial control panels and many other applications. Many NEMA enclosure suppliers will have a configuration tool to allow you to customize or select the required features and options for your application.
If using a catalog or standard part requires plenty of changes in your design to accommodate the standard enclosure part, then a custom NEMA enclosure might be a better option.
Another consideration is the need for additional modifications or retrofitting to the NEMA enclosure for your application. You should ask yourself:
Leveraging the enclosure manufacturer’s skills is typically the best option for modification and customization of an enclosure
NEMA enclosures are manufactured in a wide range of NEMA types to provide the appropriate level of protection for your application from dust to dripping or wet locations to water immersion.
NEMA enclosures are available in a wide range of shapes, configurations, mounting styles, and NEMA ratings.
Many NEMA enclosure manufacturers are familiar with the nuances and unique requirements of specific industry applications. They can provide products specialized for different industries.
NEMA enclosures can be designed and built to meet additional ratings such as:
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