Industrial Control Panel Environments
Numerous considerations go into electrical control panel design. The environmental conditions at the installation site are one of the most critical issues.
- Moisture control
- Corrosive materials
- Water/oil seepage
- Windblown dust/dirt
- Incidental contact
The list goes on, but you get the point. There are many variables to consider when choosing the cabinet itself. Standards associations provide guidelines for cabinet ratings and control design.
- ANSI - American National Standards institute
- CSA - Canadian Standards Association
- CE - Conformite Europeene
- EEMAC - Electrical/Electronic Manufacturers Association of Canada
- EIA - Electronic Industries Association
- FCC - Federal Communications Commission
- IEEE - Institute of Electrical and Electronics Engineers
- IEC - International Electrotechnical Commission
- SAE - International Society of Automotive Engineers
- Joint Industry Council
- NEMA - National Electrical Manufacturers Association
- NFPA - National Fire Protection Association
- UL - Underwriters Laboratories Inc.
How does the cabinet choice impact internal design?
NEMA, UL, and CSA rating is a cabinet for indoor or outdoor use is a reasonably standard enclosure for electrical controls.
Heat dissipation is a significant consideration for electrical control panels.
One of the significant considerations for electrical panels is the dissipation of heat from electronic components and wiring. If you aren’t familiar with industrial thermal control, a good example is a laptop computer. With most brands, you will feel the battery’s heat and more so if it is plugged into the charger.
The battery itself gives off heat due to the chemical changes and current flow in the battery. When plugged into a charger, there is more current flowing into the battery and running the electronics that give off heat.
In a laptop, the transformer that steps the voltage down from 120 V to 5-9 Volts to run the electronics is outside the device as part of the cord. The block of plastic containing the stepdown transformer that is part of the cord also gives off heat.
Desktop computers and other devices that plug directly into a wall socket but run on lower electronic devices required built-in fans to dissipate heat from the transformer. Many laptops have very small fans to help with heat dissipation.
The typical control panel packed with circuits, switchgear, relays, or PLC devices requires serious consideration to heat dissipation. Don’t forget motors and transformers.
The type of panel that protects from the outside environment can restrict heat and air circulation dissipation. This can also lead to moisture forming on components from humidity.
Control panels are in all types of environments.
It might not be challenging to design components and wiring in a control panel if there was only one variable. When a panel is located outside exposed to weather conditions as well as protect against unnatural elements like humans and animals it becomes difficult.
A panel has to protect humans and animals from coming into contact with the electronic/electrical devices for their protection. Plus, animals can do considerable damage when attracted to the panel’s interior for shelter or warmth in winter months.
Summers and Winters
The definition of summer protection changes with geographic locations. Summer in Canada is a lot different than Florida. Image control panels above the northern circle in Alaska controlling pipeline and oil production compared to those in Saudi Arabia or Iraq. Same function for the control systems being housed inside the panels but quite different design variables.
The hazardous material environment in petrochemical process lines or the wind and dust of the desert or oil fires? What about blizzards and sub-freezing temperatures? You get the point.
Oil fire in Iraq oil fields.
Temperature measured 3-4 feet around the outside of the cabinet is considered the “ambient temperature.” The temperature inside the cabinet near the control equipment is considered “surrounding air temperature.” The difference between the two is a two-edged sword.
When the temperature is cooler outside and warmer inside, natural convection can help dissipate the components’ internal heat. Where there is high humidity, the dew point increases beyond the internal temperature, moisture can form on the interior surfaces.
We all know that moisture and electronics don’t mix.
One of the essential requirements for the dissipation of heat from electronic components is air circulation. A panel enclosure designed to protect from outside elements may hinder the inside air circulation taking heat outside the cabinet. This is also true of bringing in cooler air for natural convection or circulation.
A Hoffman Nema 4X enclosure for electrical control circuits.
Note there aren’t any vents for introducing natural or force air convection for cooling. The electronic control systems are compact enough to require cooling. It is possible to port air in through conduits for cooling. A remote location makes this less likely.
Internal locations on factory floors and alongside production lines can create moisture headaches. Heating internal components are not just for cold temperatures.
The amount of moisture air can hold increases with temperature. If you live in a tropical climate and have an airconditioned house, you will often see moisture outside your windows in the mornings. The cooler air’s moisture being held outside condenses on the cooler surface of the window panes.
It is also why hurricanes can dump so much moisture as rain. The warm air at the surface holding the moisture rises into the cooler air at higher altitudes. Down comes the rain, water that the atmosphere at cooler temperatures can no longer contain.
Electrical components inside enclosures below the dew point
According to the National Weather Service
“The dew point is the temperature the air needs to be cooled to (at constant pressure) in order to achieve a relative humidity (RH) of 100%. At this point, the air cannot hold more water in the gas form. If the air were to be cooled, even more, water vapor would have to come out of the atmosphere in the liquid form, usually as fog or precipitation.’
In an electrical enclosure that excess moisture forms on flat surfaces, causing all sorts of issues. The moisture directly on components or circuits can cause shorts and fires—the water dripping off the surfaces can cause even larger shorts on circuit breakers or relays.
Corrosion can also be an issue once it forms, preventing components from operating correctly. Contacts in relays that won’t conduct electricity from one contact to another due to corrosion can be detrimental to the control circuit.
Mitigating condensation in control cabinets near food and beverage production lines creates a unique environment for creating moisture inside the cabinets. Temperature differentials between the enclosures and surrounding processing equipment can create condensation inside the cabinet.
Food & beverage processing lines are often warm, containing lots of moisture due to the process or washdowns at the end of a shift. When the process line off, the control circuits can cool down within the cabinets. Any moisture in the air within the cabinet can account for condensation on the components as the cool down.
How does all the moisture get into the cabinets? Even the most sealed cabinets often get opened for maintenance or adjustments during a production shift introducing warm air carrying lots of moisture. As the internal components cool down to the dew point, water will start to form on surfaces.
Preventing moisture from forming on electrical components
Inside and outside environments react to temperature differences and due points the same. The rules of physics don’t change with inside or outside enclosures.
There are many different tools to help prevent moisture damage inside electrical control enclosures. Once the environment variable is addressed and the application’s enclosures, electrical control engineers, can then choose components that reduce moisture damage potential.
Thermostats and hydrostats are used for industrial thermal management control systems within each enclosure. Separate from the process control circuitry enclosed in the cabinet, these sensing components are paired with heaters and coolers to maintain proper temperatures and humidity within the enclosure.
Thermostats in cabinet control systems work as they do in your home. When the temperature gets above a set temperature, it will turn on a cooling device. When the electrical devices are turned off, and the thermostat senses the low set-up temperature, it will turn on a heater to keep condensation from forming components
Hydrostats are used to control the relative humidity inside the enclosures. When they sense humidity outside the parameters set, they will turn on or off heaters and cooling devices in the enclosure to return to a safe temperature and humidity. Heaters controlled by the thermostat or hydrostat can take many different forms. Popular heaters for enclosures and electrical circuits are designed specifically for the purpose. Small wattage devices that are very efficient and don’t require a lot of room or electricity. Efficiency comes from the type of heater and the direct transfer of heat to the required area.
Space heaters are not the ideal solution for an electrical enclosure. Natural convection, fan-driven, and direct contact heaters are more efficient. Space heating may need to raise the temperature too much to reach individual components or circuitry.
PTC heating elements can be used for this purpose. Not only do they supply heat directly and efficiently to components, but they have built-in safety factors and often don’t require a control circuit. The PTC heating elements are embedded in fin heaters for natural and forced-air heating. Aluminum fins for direct contact with surfaces are also used. These elements are tiny and can be used safely directly on component surfaces.
Flexible etched silicon rubber heaters are also used because of the then diameters and ability to flex and bent and fastened directly onto surfaces. This results in better heat transfer and efficiency.
Peltier coolers are unique cooling devices that don’t require freon of other types of refrigeration. The cooling effect is electronic, allowing the device to be placed in direct contact with the surfaces to be cooled.
With no refrigerants or other liquid to transmit the cooling, these devices are ideal for cooling electronic components. They also do not require large amounts of electricity to run motors or fans like typical refrigeration systems.
This blog explains more about how Peltier cooling systems work. “Peltier Effect Cooling”
PTC Condensate Evaporators are an ideal solution for panel enclosures to remove excess moisture from the air. DBK evaporator is maintenance free with no draining necessary. With an evaporation rate up to 245ml/h or 8.28 oz/h the reliable PTC device makes a great choice.
Need help with heating, cooling, and evaporation panel controls?
DBK USA has experts standing by to answer your questions. Design engineers can utilize the handing power calculator on our website.
Feel free to call our thermal engineering specialists directly at 1-864-607-9047