What to Know When Selecting an Enclosure

NEMA enclosures house all kinds of electrical components from simple terminal blocks, to industrial automation systems, to high voltage switchgear. In industrial automation systems, NEMA enclosures often house motor controls, drives, PLC/PC control systems, pushbuttons, and termination systems. Some enclosures are shaped to be operator consoles.

AutomationDirect offers over 2,200 enclosure part numbers across NEMA 1, 2, 3, 3R, 3S, 4, 4X, 5, 6, 6P, 12, and 13 standards. Our metal enclosures are offered in a wide variety of materials such as painted steel, stainless steel, galvanized steel, and aluminum, while our non-metallic line is offered in polycarbonate and fiberglass.

What is a NEMA enclosure?NEMA Enclosure

NEMA enclosures meet the National Electrical Manufacturers Association standards for performance and protection of the electrical equipment installed within them. NEMA enclosures range in size from small pushbutton boxes to room-size panels. Enclosures are given a NEMA rating according to the types of applications the enclosure serves.

What kind of environment is your enclosure going to be in and what level of protection do you need?

Your enclosure’s primary function is to protect the equipment inside it from the surrounding environment. Therefore, you need to understand the environment where the enclosure will be located and select the appropriate level of protection. An enclosure’s level of protection is defined by its NEMA rating, which are described as follows:

  • NEMA 1 enclosures are typically used for protecting controls and terminations from objects and personnel. This style of enclosure, while offering a latching door, does not have a gasketed sealing surface and are used in applications where sealing out dust, oil, and water is not required.
  • NEMA 2 enclosures are intended for indoor use primarily to provide a degree of protection against limited amounts of falling water and dirt.
  • NEMA 3 enclosures are intended for outdoor use primarily to provide a degree of protection against windblown dust, rain, sleet, and external ice formation.
  • NEMA 3R enclosures are typically used in outdoor applications for wiring and junction boxes. This style of enclosure provides protection against falling rain, sleet, snow, and external ice formation. Indoors they protect against dripping water. This style of enclosure does not have a gasketed sealing surface. Some models have hasps for padlocking.
  • NEMA 3S enclosures are intended for outdoor use primarily to provide a degree of protection against windblown dust, rain, sleet, and provide operation of external mechanisms when ice laden.
  • NEMA 4 enclosures are used in many applications where an occasional washdown occurs or where machine tool cutter coolant is used. They also serve in applications where a pressurized stream of water will be used. NEMA 4 enclosures are gasketed and the door is clamped for maximum sealing.
  • NEMA 4X enclosures are made of stainless steel, aluminum, fiberglass, or polycarbonate. NEMA 4X enclosures are used in harsh environments where corrosive materials and caustic cleaners are used. Applications include food, such as meat/poultry processing facilities, where total washdown with disinfectants occur repeatedly, and petro-chemical facilities, including offshore petroleum sites.
  • NEMA 5 enclosures are intended for indoor use primarily to provide a degree of protection against settling airborne dust, falling dirt, and dripping non-corrosive liquids.
  • NEMA 6 enclosures are intended for indoor or outdoor use primarily to provide a degree of protection against the entry of water during occasional, temporary submersion at a limited depth.
  • 6P enclosures are intended for indoor or outdoor use primarily to provide a degree of protection against the entry of water during prolonged submersion at a limited depth.
  • NEMA 11 enclosures are intended for indoor use primarily to provide, by oil submersion, a degree of protection to enclosed equipment against the corrosive effects of liquids and gases.
  • NEMA 12 enclosures are intended for indoor use to provide a degree of protection against drips, falling dirt, and dripping non-corrosive liquids. These enclosures are most commonly used for indoor applications of automation control and electronic drives systems, including packaging, material handling, non-corrosive process control, and manufacturing applications. Gasketed doors seal the enclosure’s contents from airborne contaminants and non-pressurized water and oil.
  • NEMA 12K enclosures with knock-outs are intended for indoor use primarily to provide a degree of protection against dust, falling dirt, and dripping non-corrosive liquids other than at knock-outs.
  • NEMA 13 enclosures are intended for indoor use primarily to provide a degree of protection against dust, spraying of water, oil, and non-corrosive coolant.

 

Determine Your Security Requirements

Your enclosure may also need to protect its contents from unauthorized access to the components it houses. AutomationDirect has options to meet a wide variety of security needs. For low-risk installations, a screw cover, lift-off cover, or single-door with clamps may be sufficient. In higher risk installations, an enclosure with keylocking and/or padlocking capabilities may be needed.

If you cannot find a stock enclosure with the security features that you need, AutomationDirect offers replacement locks and latches that you can retrofit to your enclosure.

First, determine the height and width for your enclosure by laying out the footprint space needed for your control components on a standard subpanel size. Remember to consider the mounting holes for the subpanel when planning the required footprint space. The size of the enclosure will determine if you need a single-door, two-door, wall-mount, floor-mount or freestanding enclosure.

Next, you’ll need to determine your enclosure depth. Remember that the subpanel mounting takes up a small portion of the depth. Also, any pushbuttons, operator interfaces, indicators, meters, etc. that you plan to mount on the enclosure door will occupy some enclosure depth.

Finally, you must allow for heat dissipation. If you have estimated component sizes or heat generation, it’s always better to oversize the enclosure when you have the available space.

 

Determine Your Thermal Management Needs

Your enclosure must be able to dissipate the heat generated by the components inside of it either alone or by adding a cooling device. Heat inside an enclosure can decrease the life expectancy of controlling units such as your PLC, HMI, AC drives and other items. Excessive heat can cause nuisance faults from your electrical and electronic components: for example, overloads tripping unexpectedly. Heat will also change the expected performance of circuit breakers and fuses, which can cause whole systems to shut down unexpectedly. So, if you have any electronic equipment or other heat sensitive devices, you may need cooling.

The same items that can be damaged by heat may also be a source of the heat inside the enclosure. These include items such as:

  • Power supplies
  • Servos
  • AC Drives/inverters
  • Soft starters
  • Transformers


  • PLC systems
  • Communication products
  • HMI systems
  • Battery back-up systems

Internal heat load is the heat generated by the components inside the enclosure. The preferred method is to add the maximum heat output specifications that the manufacturers list for all the equipment installed in the cabinet. This is usually given in Watts (W). But some cooling calculations are British Thermal Units per Hour (BTU/H). So use the following conversion to convert between BTU/H and W wherever needed:

3.413 BTU/H = 1 Watt

Example: The Watt-loss chart for the GS3 Drives shows that a GS3-2020 AC drive has a Watt loss of 750 watts.

Qin = 750W x (3.413 BTU/H/W) = 2559 BTU/H

Heat load transfer is the heat rejected (negative heat load transfer) or gained (positive heat load transfer) through the enclosure walls with the surrounding ambient air. This can be calculated by the following formulas:

A = 2 [(H x W) + (H x D) + (W x D)] / (144 in2/ft2), where:

A = enclosure surface area, ft2
H = enclosure height, inches
W = enclosure width, inches
D = enclosure depth, inches

Note: Only include exposed surfaces surrounded by ambient air in surface area calculations. For example, a wall mounted enclosure formula should exclude the rear face of the enclosure.

A = {(H x W) + 2 [(H x D) + (W x D)]} / (144 in2/ft2

Freestanding enclosures, enclosures in corners, etc. are other situations where you should use a modified formula to account only for the exposed surfaces.

Qt = h x A x (Tac – Tmax), where:

Q = heat load transfer, BTU/H
h = heat transfer coefficient, BTU/(H∙ft2∙°F)
Tac ≡ maximum ambient air temperature, °F
Tmax ≡ maximum allowable internal enclosure temperature, °F

The heat transfer coefficient, h, represents how easily a particular material transfers heat to the atmosphere. Use the following coefficients to calculate heat load transfer:

Painted or galvanized steel: h = 0.97 BTU/(H∙ft2∙°F)
Stainless steel: h = 0.65 BTU/(H∙ft2∙°F)
Aluminum: h = 2.11 BTU/(H∙ft2∙°F)
Non-metal: h = 0.62 BTU/(H∙ft2∙°F)

Note that where Tin > Ta, the heat load transfer is negative, which means the enclosure will reject some or all of the heat load to the atmosphere without additional cooling. Also note that in those cases, the rate that heat is rejected can be increased by increasing the surface area of the enclosure, which means that you may be able to side-step additional cooling simply by upsizing your enclosure to increase the surface area through which heat is transferred to the atmosphere.

Other external sources of heat can also cause the internal temperature of your enclosure to rise above a desired level due to thermal radiation. These include items such as:

  • Industrial ovens
  • Solar heat gain
  • Foundry equipment
  • Blast furnaces

Calculations for determining the heat load due to thermal radiation are complex beyond the scope of this document. If thermal radiation heat sources are present, the heat gain should be determined by a qualified engineer.

Once you have determined your Internal Heat Load and the Heat Load Transfer, you can choose the proper size air conditioning unit by calculating the needed cooling capacity:

QC = Qin + Qt + Qr, where:

QC = enclosure required cooling capacity, BTU/H
Qin = total internal heat load, BTU/H
Qt = heat load transfer, BTU/H
Qr = heat transfer from thermal radiation, BTU/H

Note: Always remember that heat load transfer (Qt) may be negative if the maximum ambient temperature is lower than the maximum internal temperature, which is usually the case in climate-controlled, indoor environments.

If QC < 0, the enclosure will be able to reject enough heat to the atmosphere to maintain the temperature below the maximum allowable temperature. But if QC > 0, additional cooling will be required.

If additional cooling is required, AutomationDirect has many devices to choose from. But always remember that the heat dissipation method you select must be compatible with the enclosure’s NEMA rating.

For some applications, simple louver plates with or without filters will provide adequate heat dissipation through natural convection. 

 

Natural Convection Cooling
Natural Convection Cooling

If the ambient temperature outside the enclosure is cooler than the inside of the enclosure, the addition of louvers or grilles with filters will allow warm air to vent from the enclosure and be replaced by cooler outside air. If the required cooling capacity is low, this method may allow enough heat to be dissipated to meet the enclosure’s cooling requirements. Calculations to accurately assess the effectiveness of cooling using only natural convection are complex beyond the scope of this document.
Since they are open to the atmosphere, open louver plates can only maintain a NEMA 1 or NEMA 2 enclosure rating. For the same effect on enclosures with up to a NEMA 12 rating, exhaust and intake grilles with filters may be used.

 

Forced Convection CoolingForced Convection Cooling

If you have clean and cool ambient air outside of the enclosure and need more, then a fan and grille combination is your next most economical cooling option. The fans create forced air convection cooling, which increases the cooling capacity by increasing the rate by which heat is removed from the enclosure and rejected to the outside.
To select the proper size fan, you need to determine the air flow rate that the fan will need to generate:

 

 

 

 

ΔTC = Tmax – Tac, where:

ΔTC ≡ inside/outside temperature difference, °F
Tac ≡ maximum ambient air temperature, °F
Tmax ≡ maximum allowable internal enclosure temperature, °F

P = QC / 3.413 BTU/H/W, where:

P ≡ Power to be dissipated, W
QC ≡ enclosure required cooling capacity, BTU/H
CFM = (3.17 °F∙ft3/W∙min) x P / ΔTC, where:
CFM ≡ fan airflow, ft3/min

When selecting a fan, be sure to use the fan’s airflow with grilles and filters, which accounts for the restriction of flow by these components. Also, be aware that unless a special hood is included, fan systems can typically only maintain a NEMA 12 rating. Further, in dusty or dirty environments the filters in a fan system will have to be cleaned or replaced frequently.

 

Closed Loop CoolingClosed Loop Cooling

If the environment is harsh, there are washdown requirements, heavy dust and debris or the presence of airborne chemicals, you need a system that will keep the ambient air separate from the internal enclosure air. Closed loop cooling systems, which include air conditioners and air-to-air heat exchangers, and vortex coolers can meet these requirements.

 

Closed Loop Cooling: Using a Heat Exchanger

An air-to-air heat exchanger is an option if you have cooling requirements that could be handled by a fan, but need a closed loop system to maintain a high level of protection for the components inside the enclosure. As with a fan system, the outside air must be cooler than the air inside the enclosure for the heat exchanger to be effective.

Heat exchangers are sized by cooling capacities per degree of temperature difference. To calculate the minimum heat exchanger capacity required:

Qhx = QC / (ΔTC x 3.413 BTU/H/W), where:

Qhx ≡ Minimum heat exchanger capacity, W/°F
QC ≡ enclosure required cooling capacity, BTU/H
ΔTC ≡ inside/outside temperature difference, °F

 

Closed Loop Cooling: Using and Air Conditioner or Vortex Cooler

If the ambient temperature is as high as or higher than the desired internal temperature, either an air conditioner or a vortex cooler will be required to cool the enclosure. Both are typically sized using the required cooling capacity (Qc) calculated earlier.

To select the proper size air conditioner, the worst-case conditions should be considered, but take care not to choose an oversized unit, as both the initial cost and the operating cost increase with size. You should also make your selection using the cooling curves for each air conditioner, as any air conditioners available cooling capacity is going to vary depending upon the ambient temperature. Do not rely on the unit’s nominal cooling capacity, as that is simply a representative number.

Vortex coolers are often an attractive alternative to air conditioners, particularly on small enclosures or non-metallic enclosures where an air conditioner cannot be mounted. Vortex coolers use compressed air to create a stream of very cold air that is injected into the enclosure. The purchase price of a vortex cooler system is typically much lower than for an air conditioner. However, they consume large volumes of compressed air, so operating costs can be very high.

While not a true closed loop system, vortex coolers do prevent the entry of outside contaminants to maintain a NEMA 12, NEMA 4 or NEMA 4X rating, since the outside air that is introduced comes from a filtered compressed air source rather than the ambient environment.

Any vortex cooling system should include a filter to remove any contaminants from the compressed air stream so that they are not introduced to the interior of the enclosure. The system should also include a thermostat and a solenoid valve to shut off the airflow to the cooler when the enclosure is sufficiently cool. The output of the vortex cooler is typically well below freezing, so continuous operation without thermostatic control may cause ice formation inside the enclosure.

 

Enclosure Heating

An enclosure may also require heating where environmental conditions are conducive to condensation and/or ice formation inside the enclosure. Enclosure heaters protect electrical/electronic components from condensation moisture buildup that can result in corrosion and component failure.

Moisture and corrosion will remain low if relative air humidity stays below 60%. However, relative humidity above 65% will significantly increase moisture and corrosion problems. This can be prevented by keeping the environment inside an enclosure at a temperature as little as 9°F (5°C) higher than that of the ambient air. Constant temperatures are a necessity to guarantee optimal operating conditions. Continuous temperature changes not only create condensation but they reduce the life expectancy of electronic components significantly. Electronic components can be protected by cooling during the day and heating at night.

Heaters are available in various heating capacities, operating voltages, and mounting options. Larger capacity heaters include a fan to circulate heat inside the enclosure. Some models include integral thermostats.

Calculations for sizing a heater include many of the same elements as used in sizing cooling components. The primary difference is that heating calculations use the minimum temperature or energy parameters of the system rather than the maximum.

ΔTH = Tmin – Tah, where:

ΔTH ≡ inside/outside temperature difference, °F
Tah ≡ minimum ambient air temperature, °F
Tmin ≡ minimum allowable internal enclosure temperature, °F

Note that for most applications, Tmin = 41°F (9°F above freezing) is sufficient. Many heaters include thermostats preset to 41°F.

For enclosures located indoors:

PH = h x A x ΔTH – PV, where:

PH ≡ inside/outside temperature difference, W
PV ≡ total heating power generated by internal components, W

For enclosures located outdoors:

PH = 2h x A x ΔTH – PV

The heat transfer coefficient, h, is the same as the one used in the cooling calculations above. But since heating calculations are in Watts, it will be easier to use heat transfer coefficients converted to W/(ft2∙°F):

Painted or galvanized steel: h = 0.284 W/(ft2∙°F)
Stainless steel: h = 0.191 W/(ft2∙°F)
Aluminum: h = 0.691 W/(ft2∙°F)
Non-metal: h = 0.181 W/(ft2∙°F)

As noted in the equation above, the heat transfer coefficient is doubled for outdoor installations to allow for increased heat loss due to wind.

The total heating power, PV, is generally going to be the same value as the internal heat load, Qin, used in the cooling calculations, expressed in Watts instead of BTU/H. However, there may be instances where the heat output for an internal component may vary. In this case be sure to use the minimum heating power generated by each component. In cases where a component may not be continuously energized, this value may be 0.

 

Choose Your Accessories

AutomationDirect offers a wide range of accessories for our enclosures.


  • Subpanels – our enclosures do not come with subpanels unless specified in the product description.
  • Mounting alternatives – floor stand kits, mounting feet, casters, and pole-mounting kits
  • Drip shields for outdoor enclosures
  • Window kits
  • Folding shelves
  • Hole seals and hole plugs
  • Adapter plates for disconnects
  • Grounding accessories
  • Replacement locks and latches



  • Electrical interlocks
  • Print pockets
  • Panel-mounting accessories – swing-out panel kits, adjustable depth-mounting kits, panel supports for heavily-loaded panels, and dead front kits
  • Frames, channels and rails for rack-mounted equipment
  • Terminal brackets and straps, mounting channels, grid straps, and DIN-rails
  • Touch-up paint
  • Replacement gaskets

 

Originally Posted: Sept. 9, 2013