A Practical Guide to Electronic Enclosure Design

Enclosure Design for Environmental Controls

Electrical controls and power enclosures cover a wide range of types, mounting, and applications. An enclosure may be indoor or outdoor, and floor mounted, pole-mounted, or pedestal.

An equal number of sizes and levels of protection from the elements and for safety are available. These variables have some influence on the interior design of the electronic equipment and switchgear within the enclosure.

Numerous electrical standard agencies dictate best practices for safety and local codes for building and wiring. All of the standards are readily available now by the internet and your company probably already follows best practices for adhering to the regulations and safety.

This article primarily deals with industrial type enclosures found in manufacturing facilities around the world. The type enclosure and electronics that control production lines and factory equipment. Designers can apply the logic introduced to other control enclosures like security and safety systems, remote gas & oil pipeline control systems, and even windmills.

The basic layout of power and electronics in industrial enclosures

Outside the codes and regulations is a design that facilitates equipment maintenance while adhering to the safety standards. You might have noticed stickers on panels or electrical enclosures that specified that only qualified individuals should open the panel or work on the equipment housed inside.

Unfortunately, several things can happen when an unauthorized or trained person gains access to the components inside the panels.  

Safety is the primary concern. The switchgear, electrical connections, and devices are exposed to contact. That contact can result in burns, electrocution, and death. Even an experienced electrician or electrical engineer can contact live circuits, resulting in painful results. An inexperienced individual coming in contact with a power circuit can be deadly.

It is advisable to always turn off the power before opening a control panel. There are occasions where service and maintenance need doing without shutting down. Organized wiring and spacing are even more critical when working on these types of systems.

When the manufacturer and designer take the time to organize the internal circuits and controls logically, they will be safer and easier to maintain.  

Best practices and logical arrangements

When possible, it is important to orientate the switchgear that controls the incoming power so that it can be shut off before opening the cabinet. Panels exposed to the public like traffic and safety panels don’t have access to switchgear externally since they don’t want someone to shut off the power supply. These types of cabinets have locked entry with the switchgear controls internally mounted.

Industrial control panels have switchgear with levers protruding from the panel to be turned off or on before opening or closing the panel doors. Of caution, even these panels will have hot terminals on the input side of the circuit breaker. A practical mounting for this type of switch is near the top right corner of the panel. This positioning keeps the input terminals out of reach for most repairs or maintenance.

A wrench or breaker bar coming into contact with 3 phase 240-480 Volt line power can become a disaster.

Electrical power and signal routing

Industrial enclosures powered by 240V - 480V 3 phase circuits with step-down transformers for control voltage of 110V for contactors and relays can create a lot of heat. There is a multitude of different combinations of this typical layout. Transformers and power wiring can give off heat and also electromagnetic interference.

These issues and safety concerns, keeping power away from signal or low voltage wiring power wiring should be kept separate from control circuitry and wiring. Individual cable trays run up or down the panel switchgear side, branching off to the control contacts and relays.

Some designers will keep the power circuits on the right side of the cabinet and control circuits on the left. The two types of wiring and circuits have to come together at some point. A good practice is to have the power wiring at the bottom or top of each set of controls mounted on DIN channels and control circuitry at the opposite end of the relays or contactors.

The same is true of circuit boards or other instrumentation devices. Power on one side and signals on the other are consistent through-out the cabinet.

Through the panel gages and switches

Applications may require through the panel controls, switches, or the ability to monitor gages. Gages are viewed through plexiglass or glass windows, while controls and switches have to penetrate the panel enclosure.

Depending on the panel rating and exterior environment, the protruding switches and buttons will require appropriate sealing against the elements. It is the interior routing of the control wiring on the surface of the panel's door that needs consideration.

When the enclosure door is closed, is the control wiring in the interior power devices' proximity or wiring? If so, electromagnetic interference can be an issue. Proper design will have the power wiring and switchgear mounted in areas away from the door's control wiring.

Maybe more apparent, the internal components of the door-mounted controls should mount such that they don’t come into contact with power components or proximity. 

Enclosure design for environmental controls

The environmental requirements for organizing internal devices and components need careful consideration. The primary enemy of panel enclosed control systems is heat generated by the interior features. Operating ranges vary for individual components, but it is safe to assume that any device's lowest operating temperature within the enclosure is the target temperature. 

For lack of a better term, the target temperature is the highest temperature the cabinet's interior can reach before the potential for component failure. A designer may place those components at the bottom of the enclosure since warmer temperatures are found at the top.

If air circulation or air conditioning is possible, the warm air should exit the top of the enclosure, and cooler air enters the bottom, supporting natural heat convection. As often as not, a variety of exterior temperature conditions will exist at the panels' location. If the panels are located outside, they will be exposed to even more significant environmental changes.

Interior heaters for cold environments are typically located toward the bottom of the enclosure or in the direct vicinity of most vulnerable areas.  

Temperature and humidity controls location is also essential. Suppose you think about your home heating thermostat. It is located in the hallway of your home. I’ve never figured that one out because I want the room's temperature to be correct, not a hallway.

The hallway is the choice because it is less likely to be affected by the sun coming through a window and adversely affecting the thermostat with its radiant heat.

In a panel, the same holds. Don’t mount the temperature sensors on the inside surface of a panel exposed to the sun. Mounting components on the DIN rails near the middle of the panel will usually work well.

The same is true with hydrostat sensing devices. Mounting on the DIN rails near the center of the enclosure offers the best solution for average temperature and humidity in the cabinet. 

Just remember that the temperatures and humidity throughout the enclosure will vary. If you were to put RTD or other sensors in different panel locations, the chances are you will get different readings. Not a lot different because the overall temperature and humidity will tend to balance across the different areas unless they are isolated from each other. But they will vary.

Suppose the panel required an interior air cooling device like a Peltier Cooler mount it toward the top of the panel where the cold air will naturally move downward. If installed to protect an individual device can be attached to the device's surface or where the airflow is directed at the component.

Top choices for enclosure temperature & humidity controls

DIN rail mounted temperature, and humidity controls are the easiest to incorporate in the electronic control panel circuitry. This orientation also allows for the same separation of power and control wiring and raceways to protect and isolate the wiring.

Surface heating components

An enclosure may house components that must maintain a specific temperature such as medical equipment or food processing. In these cases, a surface mounted PTC heating device may be the right choice. It will be directly mounted to the surface to maintain a set temperature and transfer the heat to the mounted component or container.  

A PTC heating element is self-regulating and automatically adjusts its input based on the internal cabinet temperature; it is suited for this purpose without a closed-loop control system.

Convection heating components

These DIN rail mounting devices have the same characteristics as other PTC heaters for safety and set-point temperature control. PTC convection heating elements are internally mounted to aluminum fins that help dissipate heat to the surrounding area. As heat rises, they will typically be mounted at the bottom of the cabinet and respond to colder temperatures.  

If the interior of the enclosure's ideal operating temperature is 65 degrees and the PTC heating element has a similar set-point once the interior temperature goes below the set-point, the current will begin to flow, heating the device back to that desired temperature.

Fan heating components

PTC fan heaters are an excellent way to circulate the heat within the enclosure. These fan heaters can be tiny, and DIN rail mounted to be more precise where heat is circulated. Larger PTC fan heaters can cover larger internal space or distributed heat among multiple cabinets if necessary.

Same as the other two PTC heaters, these don’t require control circuitry or temperature sensors. The control circuitry can be added if needed in unique configurations. Many of the fan heaters have isolated circuitry for power and control.

Hydrostats and humidity control devices

A hydrostat is a thermometer for humidity. The hydrostat is more efficient than a thermostat for controlling the temperature in an enclosure to prevent humidity, forming water droplets on surfaces.

The hydrostat disregards temperature and only turns on heating when the relative humidity set-point is reached. It then switches off when the delta between the actual temperature and relative humidity remains below the due point.

A condensate evaporator could also be a solution. Relatively small PTC condensate evaporators are another solution for reducing humidity in enclosures.

Need help with heating, cooling, and evaporation panel controls?

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Call our thermal engineering specialists directly at 1-864-607-9047