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Modern industrial control cabinets are becoming increasingly compact while accommodating more electronic equipment than ever before. A single enclosure may now contain PLCs, variable frequency drives (VFDs), servo systems, industrial PCs, Ethernet switches, safety controllers, power supplies, remote I/O modules and industrial communication gateways—all operating continuously in a confined space.
This trend reflects the rapid development of industrial automation. Higher production efficiency, decentralized control architectures and the widespread adoption of Industrial Ethernet have significantly increased the number of electronic devices installed inside electrical enclosures. At the same time, manufacturers are under constant pressure to reduce cabinet size in order to save floor space, lower material costs and simplify machine layouts.
The result is a substantial increase in power density—the amount of electrical power and heat concentrated within a limited enclosure volume.
Many engineers associate enclosure overheating with high ambient temperatures or inadequate cooling equipment. However, field experience suggests that overheating problems rarely originate from the cooling device itself. In many projects, the root cause can be traced back to the thermal design of the cabinet during the engineering phase.
Once an enclosure enters production, adding a larger cooling unit often addresses only the symptom. The underlying thermal behavior—where heat is generated, how it accumulates and how it moves inside the cabinet—remains unchanged.
Understanding heat generation is therefore not simply a theoretical exercise. It forms the foundation of every reliable enclosure cooling strategy.
Increasing Power Density Creates New Thermal Challenges
Twenty years ago, a typical industrial control cabinet contained relatively few electronic devices. Large contactors, relays and transformers occupied most of the available space, while electronic controllers represented only a small portion of the installation. Heat generation was comparatively modest, and natural ventilation was often sufficient.
Today's control cabinets present a very different picture.
Servo amplifiers operate at high switching frequencies. Industrial PCs continuously process production data and machine vision tasks. Managed Ethernet switches support dozens of connected devices. High-performance PLCs execute increasingly complex control algorithms, while compact switching power supplies replace traditional linear designs.
Although each individual component has become more energy-efficient, the total thermal load inside the enclosure has increased because significantly more equipment now operates simultaneously.
Engineers frequently encounter situations where a cabinet designed according to electrical requirements no longer satisfies thermal requirements. Components are selected correctly, cable routing is carefully planned, and the electrical drawings are complete, yet excessive internal temperatures still occur after commissioning.
In most cases, the issue is not excessive power consumption but excessive heat concentration.
This distinction is critical.
A cabinet containing 600 W of distributed heat behaves very differently from another cabinet where the same 600 W is concentrated around several high-power drives installed within the upper half of the enclosure.
Heat density—not merely total heat load—often determines whether thermal problems develop.
Every Electrical Device Generates Heat
One of the most common misconceptions in enclosure design is that only high-power equipment such as VFDs or servo drives produces significant heat.
In reality, every electrical device installed inside a cabinet contributes to the enclosure's thermal environment.
Heat is generated whenever electrical energy is converted, regulated, switched or transmitted. Regardless of how efficient modern industrial electronics have become, no electrical component operates with perfect efficiency. A small portion of the input power is inevitably lost through semiconductor conduction, switching losses, magnetic losses or power conversion inefficiencies.
From a physics perspective, these energy losses cannot disappear. They are converted into thermal energy and released into the surrounding air inside the enclosure.
For example, a variable frequency drive operating at an efficiency of 97% still converts approximately 3% of its input power into heat. Under continuous operation, a 15 kW drive may therefore release hundreds of watts of heat into the cabinet.
The same principle applies to switching power supplies, industrial PCs, UPS systems and communication equipment. Individually, their thermal contribution may appear relatively small. Collectively, however, they create a thermal environment capable of exceeding the allowable operating limits of sensitive electronics.
This is why enclosure thermal design should always consider the combined heat generated by all installed equipment rather than focusing only on the largest power consumers.
Why Overheating Often Appears During Commissioning
One of the most frustrating aspects of enclosure overheating is that it frequently remains hidden until the machine enters full production.
During factory acceptance testing, equipment may operate under partial load, doors are opened regularly for inspection and ambient temperatures are relatively moderate. Under these conditions, cabinet temperatures often remain within acceptable limits.
After installation on site, the operating conditions change dramatically.
Production runs continuously.
Cabinet doors remain closed.
Ambient temperatures increase during summer.
Nearby machinery adds additional heat.
Drives operate under sustained load rather than intermittent testing cycles.
Only then does the enclosure begin to reveal its actual thermal behavior.
This explains why many overheating problems are discovered weeks after commissioning rather than during equipment assembly.
From an engineering standpoint, thermal design should therefore be treated as a design-stage consideration rather than a maintenance issue.
Waiting until components overheat before evaluating cabinet cooling almost always results in higher costs, longer downtime and unnecessary system modifications.
Field Experience: The Average Temperature Was Acceptable—The PLC Still Failed
During the upgrade of an automated production line, engineers were asked to investigate intermittent communication faults affecting a PLC expansion rack.
Initial inspection showed no obvious abnormalities. The enclosure air conditioner was operating correctly, cabinet temperature measurements averaged approximately 34°C, and all electrical components remained within their specified operating range.
However, infrared thermal imaging revealed a different picture.
A high-power variable frequency drive installed near the bottom of the cabinet discharged warm air upward through natural convection. Directly above the drive were the PLC CPU and communication modules.
Although the overall cabinet temperature appeared acceptable, the localized air temperature surrounding the PLC consistently exceeded 45°C during continuous production.
After relocating the drive and separating the control electronics from the high-power devices, communication stability returned without increasing the cooling capacity.
This project illustrates an important engineering principle:
Average cabinet temperature does not necessarily represent the thermal conditions experienced by individual components.
In enclosure thermal management, local hot spots often determine system reliability far more than average temperature measurements.
Experienced enclosure designers rarely begin a project by selecting a filter fan or an enclosure air conditioner.
Instead, they begin by asking three fundamental questions:
Only after answering these questions can an appropriate cooling method be selected with confidence.
In practice, improving component layout, increasing equipment spacing or redesigning airflow frequently delivers greater reliability improvements than simply installing a larger cooling unit.
For this reason, understanding heat generation should be considered the first stage of enclosure thermal engineering—not the final step after overheating has already occurred.
Now that we understand why electrical cabinets generate heat and why thermal problems often develop despite apparently acceptable average temperatures, the next step is identifying the individual components responsible for heat generation.
Not all devices contribute equally to the thermal load. Some generate only a few watts of heat, while others continuously dissipate several hundred watts under normal operating conditions. Understanding these differences is essential for accurate heat load calculation and effective enclosure cooling design.
Major Heat Sources Inside Electrical Cabinets
Once engineers understand that every electrical component contributes to the enclosure's thermal environment, the next challenge is identifying which devices generate the most heat and how that heat affects surrounding equipment.
In practice, enclosure overheating is rarely caused by a single component. Instead, it results from the combined thermal behavior of multiple devices operating continuously within a confined space.
An accurate thermal assessment therefore requires evaluating not only the rated power of each component, but also its operating efficiency, duty cycle, installation position and interaction with adjacent equipment.
The following sections examine the major heat sources commonly found inside industrial electrical cabinets.
Among all electrical components installed inside modern control cabinets, variable frequency drives (VFDs) are typically the largest continuous heat source.
A VFD controls motor speed by converting incoming AC power into DC and then back into a variable-frequency AC output using high-speed IGBT switching. Although this conversion process is highly efficient, it is never lossless. The remaining electrical energy is dissipated as heat through semiconductor conduction losses, switching losses, magnetic components and internal cooling systems.
Modern industrial drives generally achieve efficiencies between 95% and 98%. While these figures appear impressive, even a small percentage of power loss becomes significant in high-power applications.
For example:
This heat is released directly into the enclosure unless it is removed through forced ventilation or dedicated cooling equipment.
During panel inspections, VFD-related overheating is often associated with installation rather than drive efficiency.
A common design mistake is mounting multiple drives directly above one another with only the minimum mechanical clearance recommended by the manufacturer. While the spacing satisfies installation requirements, the hot exhaust air from the lower drive is immediately drawn into the upper drive, causing progressive temperature increases throughout the cabinet.
In one packaging line retrofit, three servo drives and one VFD were stacked vertically inside a narrow enclosure. Thermal imaging showed that the uppermost drive consistently operated more than 9°C hotter than the lowest unit, despite identical electrical loading.
Relocating one drive to a separate mounting column reduced internal temperatures sufficiently to eliminate repeated over-temperature alarms without increasing cooling capacity.
High-power drives should always be positioned with airflow in mind rather than purely according to wiring convenience. Whenever possible, separate drive groups from sensitive control electronics and avoid allowing heated exhaust air to pass directly across PLCs or communication equipment.
Servo drives generate heat through mechanisms similar to VFDs, but their thermal behavior is more dynamic.
Unlike conventional motor drives operating at relatively stable loads, servo systems continually accelerate, decelerate and reverse direction. Each motion cycle changes the current flowing through the power electronics, producing fluctuating heat output throughout the production process.
Robotic assembly, packaging machinery and CNC equipment often place particularly demanding thermal loads on servo amplifiers because rapid positioning requires repeated high-current operation.
For this reason, engineers should avoid estimating servo heat generation solely from rated motor power.
Instead, the actual duty cycle should be considered.
Field Observation
During machine acceptance testing, servo systems often appear to generate relatively little heat because the equipment runs at reduced production speed.
Once the machine enters full production with continuous motion cycles, enclosure temperatures increase significantly.
This explains why thermal issues associated with servo drives frequently emerge several weeks after commissioning rather than during factory testing.
Industrial PCs are frequently underestimated during enclosure thermal calculations because their electrical power ratings are relatively modest compared with motor drives.
However, unlike intermittent control devices, IPCs often operate continuously at high processor utilization.
Machine vision systems, production databases, MES communication and SCADA applications require sustained CPU performance. Nearly all electrical energy consumed by these computing processes is ultimately converted into heat.
Fanless IPCs deserve particular attention.
Although eliminating internal fans improves reliability in dusty industrial environments, heat is transferred directly to the enclosure through large aluminum heat sinks. The surrounding air temperature can therefore become considerably higher than indicated by overall cabinet measurements.
Several machine builders have reported unexplained IPC instability during summer operation despite acceptable enclosure average temperatures.
Infrared inspection often reveals localized temperatures exceeding 50°C around fanless industrial computers installed immediately beside power supplies and Ethernet switches.
Simple relocation of the IPC into a lower-temperature section of the enclosure frequently restores long-term stability without requiring additional cooling equipment.
Compared with power electronics, PLCs consume relatively little electrical power.
A typical PLC CPU together with several I/O modules may dissipate only 20–60 W during normal operation.
Nevertheless, PLCs deserve careful thermal consideration because they are considerably more sensitive to elevated temperatures than many high-power devices.
Electronic components inside CPUs, communication modules and memory circuits may continue operating within specification, yet prolonged exposure to elevated temperatures accelerates capacitor aging and reduces long-term reliability.
Many designers assume that because PLCs generate little heat, they can be mounted immediately above VFDs or servo drives.
This is one of the most common causes of localized overheating.
The PLC itself is rarely responsible for excessive temperatures.
Instead, it suffers from heat generated by adjacent power devices.
Whenever possible, separate control electronics from major heat-producing equipment and position PLCs within the coolest airflow available inside the enclosure.
Modern switch-mode power supplies achieve efficiencies exceeding 90%, leading many engineers to underestimate their thermal contribution.
However, every conversion loss appears as heat.
For example, a 480 W power supply operating at 92% efficiency dissipates approximately 38 W.
A cabinet containing four identical power supplies therefore introduces more than 150 W of continuous heat before considering any other equipment.
Power supplies also experience reduced efficiency at elevated temperatures, meaning thermal conditions can further increase heat generation.
Avoid installing multiple high-capacity power supplies immediately beside one another unless adequate airflow is available between units.
Network equipment rarely receives significant attention during enclosure thermal design because individual switches consume relatively little power.
Nevertheless, Industrial Ethernet infrastructure now operates continuously throughout modern factories.
Managed switches, fiber converters and PoE devices may consume 20–80 W each.
When grouped together inside communication cabinets, their combined heat output becomes substantial.
Unlike motor drives, network equipment often lacks dedicated internal cooling fans, making ambient cabinet temperature particularly important for long-term reliability.
UPS units generate heat from several independent sources.
Power conversion losses occur during normal operation.
Additional heat is produced while charging batteries.
During power disturbances, inverter operation further increases thermal loading.
Lead-acid batteries are especially sensitive to elevated temperatures.
A widely accepted engineering guideline indicates that every 10°C increase above the recommended operating temperature can significantly shorten battery service life.
For this reason, UPS installations should never be evaluated solely from an electrical perspective.
Battery temperature management is equally important.
One of the most common mistakes in enclosure thermal design is assuming that the largest power consumer automatically creates the greatest thermal risk.
In reality, thermal reliability depends on three factors:
A cabinet containing 500 W of evenly distributed heat often performs better than another containing 350 W concentrated within a small area around drives, power supplies and communication equipment.
Experienced engineers therefore evaluate not only the thermal output of individual devices but also their physical arrangement inside the enclosure.
Understanding the relationship between heat source, equipment layout and airflow is the key to preventing localized hot spots and ensuring long-term system reliability.
Why Hot Spots Form Inside Electrical Cabinets
When discussing enclosure cooling, many engineers focus on one number—the total heat load.
Heat load calculations are undoubtedly important, but they tell only part of the story.
In practice, equipment failures are rarely caused by the average cabinet temperature. Instead, they are often triggered by localized hot spots, where temperatures are significantly higher than the enclosure average.
This explains why two cabinets with the same calculated heat dissipation can perform very differently in the field.
One enclosure may operate reliably for years, while another experiences repeated PLC communication faults, drive over-temperature alarms, or unexpected controller resets within months of commissioning.
The difference lies not only in how much heat is generated, but in how that heat moves, accumulates, and interacts with sensitive equipment inside the enclosure.
Heat Does Not Distribute Evenly
One of the most common misconceptions in enclosure thermal design is assuming that internal air temperature is uniform.
It is not.
Inside a closed cabinet, heat naturally follows the principles of convection.
Warm air rises.
Cooler air sinks.
As electronic devices continuously release thermal energy, a vertical temperature gradient gradually develops.
Under normal industrial operating conditions, it is not unusual to measure a temperature difference of 8–15°C between the lower and upper sections of a cabinet.
The exact value depends on enclosure dimensions, equipment layout, ambient temperature, and airflow conditions.
This means that a temperature sensor installed near the bottom of the enclosure may indicate 32°C, while electronic modules mounted near the top experience air temperatures exceeding 45°C.
For thermal-sensitive electronics, that difference can determine whether the system operates reliably or fails intermittently.
How Local Hot Spots Develop
A hot spot is not simply an area with high temperature.
It is a location where heat is generated faster than it can be removed.
Several factors usually combine to create this condition.
During cabinet assembly, installers often group variable frequency drives, servo amplifiers, braking resistors and switching power supplies together to simplify wiring.
Electrically, this arrangement is convenient.
Thermally, it is one of the worst possible layouts.
Each device releases warm air.
When installed with minimal spacing, the heat emitted by one component immediately enters the cooling path of the next.
Instead of cooling fresh ambient air, the upper device repeatedly draws pre-heated air through its heat sink.
The result is cumulative temperature rise.
Even when every device operates within its rated load, localized temperatures continue increasing until thermal equilibrium is reached.
Unfortunately, that equilibrium may already exceed the recommended operating temperature of nearby electronics.
Natural convection is the primary cooling mechanism inside many sealed electrical enclosures.
However, it depends on an uninterrupted airflow path.
Cable bundles, oversized wire ducts, improperly positioned mounting plates, and densely packed components can all obstruct the upward movement of warm air.
Once airflow becomes restricted, heat accumulates in confined regions rather than circulating throughout the enclosure.
The cabinet may contain sufficient air volume overall, yet individual components continue operating inside stagnant pockets of hot air.
These areas are often impossible to identify without thermal imaging.
Another frequently overlooked issue is heat recirculation.
This occurs when warm exhaust air from one device is immediately drawn back into the intake of another.
The problem is especially common when multiple VFDs or servo drives are installed vertically with only the minimum mechanical clearance specified by the manufacturer.
Although each drive includes its own cooling fan, none receives cool intake air.
Instead, every drive recycles progressively hotter air from the device below.
The thermal load therefore increases from bottom to top, even when electrical loading remains identical.
Cabinet temperature does not depend solely on internal heat generation.
Ambient conditions also play an important role.
A cabinet operating comfortably at 25°C ambient temperature may experience thermal problems during summer production when surrounding air exceeds 40°C.
Outdoor installations face an additional challenge.
Direct solar radiation can add several hundred watts of extra thermal energy to the enclosure surface.
As a result, the cooling equipment must remove both internally generated heat and externally absorbed heat.
Ignoring solar gain is one of the most common reasons outdoor electrical cabinets become overheated despite apparently adequate cooling capacity calculations.
Engineering Mistakes That Cause Cabinet Overheating
Based on field service experience, overheating problems are usually caused by design decisions rather than equipment failure.
Several mistakes appear repeatedly across different industries.
Mistake 1: Using Average Temperature as the Only Reference
Many maintenance teams install a single temperature sensor near the cabinet door.
When the reading remains below 35°C, the enclosure is considered safe.
However, that sensor measures only one location.
Sensitive electronics positioned near high-power equipment may be operating at temperatures more than 10°C higher.
Average temperature does not represent the thermal environment experienced by every component.
Mistake 2: Focusing Only on Total Heat Load
Calculating total heat generation is essential.
Stopping there is not.
Two cabinets can both dissipate 600 W of heat.
If one distributes heat evenly while the other concentrates it within a small area, their thermal performance will be completely different.
Engineers should evaluate heat density, not only total heat output.
Mistake 3: Mounting Control Electronics Above Power Devices
This remains one of the most common layout errors.
Power devices naturally discharge warm air upward.
Installing PLC CPUs, communication modules or industrial PCs directly above drives exposes sensitive electronics to the highest temperatures inside the enclosure.
Relocating these devices often improves reliability more effectively than installing larger cooling equipment.
Mistake 4: Ignoring Airflow During Layout Design
Electrical drawings focus on wiring.
Mechanical drawings focus on dimensions.
Thermal airflow is often considered only after commissioning.
By then, component locations are fixed.
Cable routing is complete.
Modifications become expensive.
Airflow should be treated as a design parameter from the beginning of every enclosure project.
Mistake 5: Assuming Manufacturer Clearance Guarantees Thermal Performance
Equipment manufacturers specify minimum installation clearances primarily to ensure safe operation of individual products.
They do not guarantee acceptable thermal performance for the entire enclosure.
A cabinet containing multiple heat-producing devices requires system-level thermal evaluation rather than relying solely on individual installation instructions.
Field Experience: When More Cooling Was Not the Solution
During the modernization of a conveyor control system, operators reported frequent drive temperature alarms during summer production.
The original proposal was to replace the enclosure air conditioner with a larger model.
Before changing equipment, engineers performed thermal imaging while the system operated under full load.
The investigation revealed that the cooling unit was functioning correctly.
The actual problem was airflow.
A large cable duct blocked the circulation path between the cooling unit and the upper section of the cabinet.
Most of the conditioned air returned directly to the cooling unit without reaching the drives.
After rerouting the cable duct and repositioning two power supplies, the highest measured drive temperature dropped by approximately 7°C.
No larger cooling unit was required.
This project demonstrates an important principle:
Poor airflow often causes overheating long before insufficient cooling capacity does.
Experienced enclosure designers rarely ask,
"Which cooling unit should we choose?"
Instead, they begin with a different question:
"How does heat behave inside this cabinet?"
Thermal reliability depends on understanding four interconnected factors:
Cooling equipment should be selected only after these questions have been answered.
In many retrofit projects, improving component layout, separating heat sources, or redesigning airflow produces greater reliability improvements than increasing cooling capacity.
This is why experienced engineers evaluate thermal behavior, not simply thermal power.
A cabinet that manages airflow effectively will often outperform another cabinet equipped with a larger cooling unit but a poor internal layout.
Ultimately, successful enclosure cooling is not determined by the size of the air conditioner or the airflow rating of a fan.
It is determined by whether the enclosure allows heat to leave sensitive components before it becomes a reliability problem.
Q 1: Why do electrical cabinets overheat even when the ambient temperature is normal?
A: Overheating is usually caused by a combination of internal heat generation, poor airflow, concentrated heat sources, and improper component layout—not ambient temperature alone.
Even in the same 30°C environment, two cabinets can perform very differently depending on how heat-generating components are arranged. Engineers should evaluate both airflow paths and equipment layout during the design stage.
Q 2: Which components generate the most heat inside an electrical cabinet?
A: The largest heat sources are typically:
Variable Frequency Drives (VFDs)
Servo Drives
Industrial PCs (IPCs)
Switching Power Supplies (PSUs)
UPS Systems
Industrial Ethernet Switches
Control Transformers
Although PLCs generate relatively little heat, they are highly sensitive to nearby hot spots and should be installed away from high-power devices.
Q 3: Is measuring the average cabinet temperature enough?
A: No.Average temperature does not reflect localized hot spots. Components near high-power equipment often operate at much higher temperatures than the cabinet average. Infrared thermal imaging or multiple temperature sensors provide a more accurate thermal assessment.
Q 4: Can a larger enclosure air conditioner solve every overheating problem?
A: Not always.If poor airflow or improper equipment layout is the root cause, increasing cooling capacity may have little effect. Optimizing airflow and component placement is often a more effective solution.
Q 5: When should enclosure cooling be considered?
A: Thermal management should be included during the cabinet design stage.Early heat load evaluation helps engineers choose the most suitable cooling solution, reduces redesign costs, and improves long-term reliability.
Q 6: How is the required cooling capacity determined?
A: Cooling capacity should be calculated based on:
Total heat dissipation
Ambient temperature
Target internal temperature
Cabinet size
Installation environment
Solar radiation (outdoor applications)
Equipment duty cycle
Accurate heat load calculations are essential for selecting the correct enclosure cooling solution.
Conclusion
Heat generation is an inevitable part of modern electrical cabinets. As equipment density continues to increase, thermal management has become essential for maintaining system reliability.
Successful enclosure cooling depends not only on the amount of heat generated, but also on equipment layout, airflow, and heat distribution. In many cases, improving cabinet design is more effective than simply installing a larger cooling unit.
Understanding where heat is generated is the first step. The next is determining how much heat must be removed.
In the next guide, Cabinet Heat Load Calculation Guide, we'll explain how to calculate enclosure heat loads and select the most appropriate cooling solution based on engineering data.