Control Moisture in Electronic Enclosures
If you are an electrical engineer, project manager, or purchasing manager, controlling moisture in electrical cabinets is important to you. Moisture can cause short circuits, damage equipment, and create a fire hazard. In this blog post, we will discuss the different ways you can control moisture in electrical cabinets and some of the benefits of doing so. We will also provide some tips on how to select the right moisture control solution for your needs.
What is moisture and how can it damage electrical equipment
Moisture damages equipment when it condenses out of the air onto a cooler surface. Once the condensation starts to form on electronic components or other devices in electrical control systems bad things can happen. Water, in this case, moisture in the form of condensation doesn’t mix well with electricity.
The result isn’t just short circuits but also corrosion that affects relay contacts and other switching mechanisms. Corrosion of any contacts can inhibit current flow. The corrosion as it builds up can also cause short-circuiting of components.
The sources of moisture in electrical enclosures
Electrical panel enclosures are usually specifically designed for their environment to protect against outside elements like rain or snow or liquids used in manufacturing processes. It is difficult to totally seal larger enclosures permanently because access needs to be provided for maintenance, heating, and cooling.
The moisture most difficult to control is the moisture contained in the air inside the enclosure. This moisture must be kept in a vapor state at all times. The amount of moisture inside the cabinet depends on many factors but can be measured in terms of relative humidity.
Absolute humidity is the amount of moisture that can be contained in a volume of air at a specific temperature. The relative humidity is the percentage of moisture measured in the same volume of air compared to absolute humidity. 50 % relative humidity means that the amount of moisture in the air is 50 % of the moisture that is possible.
Another way of understanding is when the relative humidity is 95 % it won’t take much of a decrease in temperature for water to start condensing out of the air. The change of state from vapor to water creates condensation on surfaces that are cooler. Or in the case of a summer thunderstorm, the cooler air changes the moisture as vapor into raindrops.
The numbers in yellow indicate the temperature where moisture in the air will start to condense on cooler surfaces like circuit boards. More likely the cooler surface could be the top or sides of the metal enclosure where the water droplets that form can fall on electrical equipment.
As an example, let's imagine the air inside of the electrical enclosure is 90 degrees Fahrenheit. If the relative humidity is 80% and the air temperature outside the enclosure drops to just 82 degrees condensation can form on the inside of the cabinet walls. Larger temperature drops will increase the amount of condensation.
A similar problem happens when the relative humidity is high and the internal temperature of the cabinet decreases below the dew point. Condensation can start forming on internal component surfaces.
Ideally, the best preventive measure would be to limit the relative humidity inside the enclosure.
Methods to control condensate in electrical enclosures
Sealing out the moisture is the best preventive method but is difficult with larger electrical cabinets and control systems. Enclosures often need to be vented to the outside for cooling or opened for maintenance or other servicing. Or water seals decrease in effectiveness over time allowing moisture to enter the enclosure.
A popular way to minimize condensation in small enclosures is to use PTC heating elements to maintain higher temperatures in the enclosure preventing condensation. Higher temperatures can hold more moisture. What are PTC heaters?
The PTC heating elements are very small relative to the heat output and come in a number of different heat transfer configurations for convection, air, fan, and cartridge forms. The positive temperature coefficient devices are ideal for small enclosures because they automatically control heating based on the air temperature.
In larger enclosures, a temperature and humidity control system may be needed that controls both heating and cooling based on the temperature of relative humidity. This type of system requires multiple components.
Hygrostats can be used to measure and control the heater or cooling devices in the cabinet. Cabinet hygrostats can be set for specific relative humidity. Output contacts control heating and cooling circuits based on the setting. What are hygrostats?
Peltier coolers are thermoelectric solid-state devices that cool the air in the cabinet. Fans circulate air from the cooled surface of the metal plates inside the device. They are a great compact design, low maintenance solution without the need for cooling fluids. What is a Peltier Cooler?
Condensate evaporators are a beneficial part of the moisture control system to eliminate the condensation that has been collected in the cabinet. Removing the moisture collected helps reduce the moisture in the cabinet reducing the dew point even further. What is a PTC condensate evaporator?
The small compact devices use PTC heating elements to evaporate the moisture collected inside and eject it from the cabinet through a built-in hose.
The benefits of controlling moisture in electrical enclosures
Components in the electrical control enclosures include computers, and diagnostic and communications equipment. The components control manufacturing equipment, power plants, oil & gas pipelines, communication networks, traffic controls, trains, and shipping.
So it isn’t just the value of the system components at risk, it is the processes controlled outside the cabinets that could be critical and damaged if the internal components fail due to condensation.
Power transformers in underground vaults when exposed to condensation of water from rainfall can short out and cause serious damage.
An electrical panel containing controls for manufacturing plants like glass, chemicals, foods, or other goods could involve very costly downtime and closure of the plants.
With today’s supply chain issues it may take a long time to replace the damaged components and get the manufacturing lines back up producing products.
How do you configure the components to prevent moisture?
DBK USA has engineers that specialize in industrial heating and cooling controls that can provide you with guidance for your application.
Talk to an experienced thermal control engineer.