Panel Heat & Cooling

Electrical panel heat dissipation is worked out by adding up the watt losses of every component inside the enclosure — taken from manufacturer data, not from assumed efficiency percentages — and then checking whether the enclosure can reject that heat at the maximum site ambient while every component stays inside its permitted temperature. In short: Ptotal = P1 + P2 + … + Pn, compared against what the enclosure and its cooling arrangement can actually remove.

The cooling method then follows from one number: the temperature difference between the maximum permitted internal temperature and the maximum ambient at the installation point. Where that difference is comfortable, enclosure surfaces or a filter fan can do the job. Where the ambient approaches or exceeds the internal target, no fan of any size will help — ventilation cannot supply air colder than ambient, so active cooling, a different enclosure concept or component reselection becomes necessary.

The Same Panel in Two Different Rooms

Consider two electrical panels.

Both contain:

2 × 75 kW VFDs

Both are:

IP55

Both have:

1600 A incomer

But:

Panel A

Installed in an air-conditioned electrical room at:

25°C

Panel B

Installed in a hot industrial shed where ambient reaches:

45°C

Can both use the same:

Panel Size + Fan Arrangement?

Not automatically.

Electrical-panel thermal design depends on the complete heat balance:

Heat generated inside

versus:

Heat that can be removed

A panel can be electrically correct in terms of:

• Breaker rating
• Busbar size
• Cable size

and still suffer:

• VFD overtemperature trips
• PLC failures
• Capacitor ageing
• Contactor overheating
• Breaker derating
• Premature electronic failure

because internal thermal conditions were not engineered properly.

IEC 61439-1:2020 specifically includes temperature-rise verification within the LV assembly verification framework, and the current edition refocuses temperature-rise verification around the actual loaded assembly.

This guide explains how to approach:

• Component heat losses
• Natural convection
• Forced ventilation
• Fan sizing
• Panel air conditioning
• IP rating
• Ambient temperature
• VFD panels
• APFC panels
• IEC temperature-rise verification

Where Does Panel Heat Come From?

Almost every electrical component dissipates some power as heat.

Typical sources include:

• ACB
• MCCB
• Busbar
• Cable connections
• Contactors
• Control transformers
• Power supplies
• PLC
• Relays
• VFDs
• Soft starters
• Reactors
• Harmonic filters
• APFC reactors
• UPS
• Communication devices

The total internal heat load is approximately:

Ptotal = P1 + P2 + P3 + ... + Pn

where each P represents power loss in watts.

The total power loss of all heat-generating components is the starting point of every control-panel temperature-rise and cooling calculation.

Use Component Heat-Loss Data — Not Guesswork

The best source for component heat loss is:

Manufacturer technical data

For example, a VFD datasheet may specify:

• Power loss at rated load
• Heat dissipation
• Cooling-air requirement

An ACB manufacturer may provide:

• Power dissipation per pole
• Connection losses

Do not simply assume:

“VFD loss = 5%”

or:

“Breaker heat = negligible.”

Modern equipment efficiencies differ substantially by model and operating point.

VFDs Can Dominate Heat Load

VFD panels deserve special attention because the drive continuously converts power electronically.

Even a highly efficient drive can dissipate significant heat at large power ratings.

For example:

If an OEM states:

VFD heat loss = 1.5 kW

and the panel contains:

2 VFDs

then the drives alone contribute:

3 kW

before adding:

• Reactors
• Breakers
• Power supplies
• Control equipment

This is why placing several large VFDs in a compact sealed enclosure can create serious thermal problems.

Example Heat-Loss Schedule

Consider an illustrative panel:

Component	Heat Loss
VFD-1	1500 W
VFD-2	1500 W
Input Reactors	250 W
MCCBs / ACB	200 W
Control Transformer	100 W
PLC / Power Supplies / Relays	100 W
Other Losses	100 W
Total	3750 W

Actual project values must come from selected equipment data.

Now the enclosure must remove approximately:

3.75 kW of internal heat

while keeping components within their permitted temperature ranges.

Heat Does Not Disappear Inside a Bigger Panel

A larger enclosure can help because it may provide:

• More surface area
• Better natural convection
• More spacing
• Lower local heat concentration

But it does not destroy heat.

Eventually:

Heat generated = Heat removed

at thermal equilibrium.

If heat removal is inadequate:

internal temperature keeps rising until losses and dissipation balance—or equipment trips/fails.

Basic Heat-Transfer Paths

Panel heat can leave through:

Conduction

Through enclosure material.

Natural Convection

Warm internal/external air movement.

Radiation

Thermal radiation from surfaces.

Forced Convection

Fans move air through/around the enclosure.

Heat Exchanger

Transfers heat while maintaining separated air circuits.

Refrigeration / Panel AC

Actively removes heat.

The correct method depends on:

• Heat load
• Ambient
• Dust
• Humidity
• IP requirement
• Maximum component temperature

First Question: What Is Maximum Ambient Temperature?

Assume:

Maximum allowable internal temperature:

50°C

Case A

Ambient:

30°C

Temperature difference available:

20 K

Natural or forced ventilation may be feasible depending on heat load.

Case B

Ambient:

48°C

Only:

2 K

difference remains.

Simple ventilation becomes far less effective.

The ambient figure in a specification is often the one worth questioning. We have been given "40 °C ambient" for panels that were then installed on a mezzanine directly above a pharma dryer, or in a sheeted-roof shed in Vadodara where the air at panel-top height in May sits well above the room figure measured at floor level near the door. Ten kelvin of optimism at this stage removes half the available temperature difference from the cooling calculation. Our recommendation: ask for the ambient at the actual panel location and at panel-top height, in the hottest month, with production running — and if that number is not available, design to the site's worst credible condition rather than to the number in the tender.

Case C

Ambient:

55°C

but components need:

≤50°C

A fan cannot cool the enclosure below the temperature of the incoming air.

Active cooling or another system-level solution is required.

Fans Do Not Refrigerate the Air

This is one of the most important practical rules.

A ventilation fan can:

replace hot enclosure air with ambient air.

It cannot make incoming air colder than ambient.

Therefore:

If ambient temperature already exceeds the required internal temperature, adding a larger fan does not solve the fundamental problem.

You may need:

• Panel AC
• Air-to-water cooling
• Conditioned electrical room
• Component derating/reselection

depending on application.

Basic Fan Airflow Calculation

Qmin = Ptotal / [ρ × c × (Timax − Tomax)]

where:

• Qmin = minimum airflow in m³/s
• Ptotal = internal heat loss in kW
• ρ = air density
• c = specific heat of air
• Timax = maximum permitted enclosure temperature
• Tomax = maximum cooling-air ambient temperature

Dedicated thermal-calculation software gives a more precise result, because this simplified airflow calculation does not fully account for heat transfer through the enclosure walls.

Example Fan Calculation

Assume:

Internal losses:

2 kW

Ambient:

40°C

Maximum desired internal:

50°C

Using commonly published approximate hot-air values:

• air density ≈ 1.1 kg/m³
• specific heat ≈ 1 kJ/kg·K

Temperature difference:

10 K

Then:

Q ≈ 2 / (1.1 × 1 × 10)

≈ 0.182 m³/s

Multiply by 3600:

≈ 655 m³/h

So the simplified theoretical ventilation requirement is around:

655 m³/h

But this is not yet the final fan selection.

Why 655 m³/h Does Not Mean “Buy a 655 m³/h Fan”

Fan catalogue airflow may be quoted at:

free air

The actual system may contain:

• Filter
• Exhaust grille
• Dirty filter
• Duct restriction
• Internal obstructions
• Pressure drop

Therefore the installed airflow can be lower.

A design should include suitable engineering margin and the actual fan/filter performance curve.

Filter Fans

Filter fans are common in industrial panels.

Advantages:

• Simple
• Low cost
• Effective when ambient is cooler than panel interior

But limitations include:

• Dust loading
• Filter maintenance
• Reduced airflow as filters clog
• Dependence on ambient temperature
• Potential IP implications

The environmental requirement therefore matters.

We have opened drive panels in textile and chemical plants where the filter mats were completely blinded with lint and process dust, and the panel was running 10 to 15 K hotter than at handover with the fans turning perfectly. Nobody had touched the filters in two summers, and the first sign of trouble was a drive overtemperature trip during peak production in May. Fan rotation is not evidence of airflow. Our recommendation: specify a filter grade suited to the actual process dust, make the mats replaceable from the front without opening the door, and add a high-panel-temperature alarm to the PLC or SCADA so a clogged filter reports itself instead of being discovered by a production stoppage.

Fan Location: Bottom Inlet or Top Inlet?

Warm air naturally rises.

A common arrangement is:

Cool filtered air in low

and:

Warm air out high

This can support natural convection.

But the actual design should follow:

• Enclosure configuration
• Heat-source positions
• OEM guidance
• Airflow path

Do not place inlet and outlet so close that air simply short-circuits without cooling the components.

Internal Air Circulation Fans

An internal circulation fan can reduce:

hot spots

by mixing enclosure air.

But if the enclosure itself cannot reject enough heat:

internal circulation alone does not remove heat from the panel.

It only redistributes it.

This distinction is important.

Natural Convection

For relatively low heat loads, enclosure surfaces may dissipate enough heat without fans.

Whether this works depends on:

• Enclosure surface area
• Ambient
• Internal losses
• Installation against walls
• Material
• Air circulation around panel

IEC TR 60890:2022

IEC publishes a specific technical report:

IEC TR 60890:2022 — A method of temperature-rise verification of low-voltage switchgear and controlgear assemblies by calculation.

It provides an air temperature-rise calculation method and is primarily applicable to enclosed or partitioned assembly sections without forced ventilation.

This is important because:

Not every arbitrary Excel heat calculation automatically equals IEC temperature-rise verification.

Use the method within its stated applicability.

IEC 61439 Temperature-Rise Verification

IEC 61439-1:2020 includes temperature-rise verification as a key design-verification characteristic for LV assemblies.

This means a manufacturer should not claim:

“Panel is 3200 A because the busbar is large enough.”

Temperature rise depends on:

• Busbar losses
• Breakers
• Connections
• Enclosure
• Ventilation
• Component arrangement
• Simultaneous loading

The complete assembly matters.

Panel Cooling Calculation vs IEC 61439 Verification

These are related but not identical.

Cooling Calculation

Helps determine:

• Required airflow
• Fan capacity
• AC capacity
• Enclosure solution

IEC 61439 Temperature-Rise Verification

Supports the thermal performance of the complete LV assembly according to the applicable verification method.

One should not automatically be presented as a substitute for the other.

Why IP Rating Matters

Compare:

IP42 Panel

More opportunity for air exchange depending on construction.

IP55 Panel

More sealed.

IP65 Panel

Highly restricted uncontrolled air ingress.

As the enclosure becomes more sealed, natural heat removal by air exchange can become more challenging.

Therefore:

Increasing IP rating can create a thermal-design consequence.

Do not change:

IP42 → IP55

after design and assume only the door gasket changes.

VFD Panel + IP55

This is a common industrial challenge.

Customer specifies:

• 4 VFDs
• 45°C ambient
• IP55
• Compact panel

These requirements pull the design in opposite directions.

VFDs produce significant heat.

IP55 restricts uncontrolled external airflow.

High ambient reduces the available temperature difference.

Possible engineering approaches may include:

• Larger enclosure
• OEM-recommended heat-sink arrangement
• Filtered forced ventilation where compatible
• Air-to-air heat exchanger
• Panel AC
• Externalized drive heatsinks
• Component derating

This is the combination we push back on hardest at clarification stage, because the numbers settle it quickly. Four 75 kW drives at approximately 1.5 kW loss each put around 6 kW into the enclosure. At 45 °C ambient with a 50 °C internal limit, only 5 K of temperature difference is available, and the simplified airflow requirement becomes roughly 6 / (1.1 × 1 × 5) ≈ 1.09 m³/s — close to 3,900 m³/h, drawn through filters, into a panel that is also required to be IP55 and compact. No filter fan arrangement delivers that in practice.

Our recommendation: on this kind of enquiry, decide early which of the four requirements can move. Usually the answer is either panel air conditioning with a sealed enclosure, an air-to-air heat exchanger where a genuinely cooler ambient exists, splitting the drives across two sections to spread the load, or externalising the drive heatsinks into a ventilated back-of-panel duct. Freezing the enclosure size first and then looking for cooling accessories is the sequence that fails.

Panel AC

A panel air conditioner can actively maintain an internal temperature below ambient.

It is useful where:

• Ambient is high
• Heat load is high
• Enclosure needs to remain closed
• Dust is severe
• Electronics are temperature-sensitive

But panel AC also introduces:

• Capex
• Power consumption
• Condensate management
• Maintenance
• Filter/coil cleaning
• Refrigerant considerations

So it should be selected from actual heat load.

Air-to-Air Heat Exchanger

A heat exchanger keeps internal and external air streams separated.

This can help maintain enclosure protection against contaminated outside air.

But an air-to-air exchanger depends on:

Ambient being cooler than desired internal temperature.

If outside air is hotter than the target cabinet temperature, passive heat exchange cannot provide refrigeration.

Outdoor Panels

Outdoor panels introduce additional thermal loads:

• Solar radiation
• High ambient
• Low ambient
• Rain
• Humidity
• Condensation
• Dust

Enclosure thermal-calculation tools handle both indoor and outdoor cases, and take ambient conditions and altitude as design inputs.

Outdoor enclosure thermal design should therefore include:

solar/environmental conditions

rather than only internal watts.

Altitude Matters

Air density reduces at higher altitude.

That can affect:

• Convective cooling
• Fan performance
• Equipment derating

If a panel is designed for near sea level and later installed at significant altitude, thermal and dielectric performance should be reviewed.

Heat-Producing Components Should Not Be Randomly Placed

Consider:

• Large VFD
• Reactor
• PLC
• Power supply

Putting a sensitive PLC directly above a hot reactor may expose it to heated rising air.

Panel layout should consider:

• Heat source separation
• Natural airflow
• Inlet/outlet path
• Manufacturer clearance
• Maintenance space

A good GA is also a thermal design.

Respect OEM Clearance Requirements

VFDs and electronic equipment typically have minimum installation spacing and airflow requirements.

Do not reduce OEM clearance because:

“Everything fits physically.”

Physical fit does not guarantee thermal suitability.

Busbar Heat

Busbars also dissipate heat because of electrical resistance.

Heat increases particularly at:

• High continuous current
• Joints
• Connections
• Restricted ventilation

A poorly made joint can become a local hot spot even if the busbar cross-sectional area itself is adequate.

The arithmetic is unforgiving here. On a 2500 A board, an extra 10 µΩ of contact resistance at one joint dissipates 2500² × 10 × 10⁻⁶ ≈ 62 W in a few square centimetres of copper — a small number in the enclosure heat balance, but concentrated exactly where the insulation and the bolt hardware are. In our FAT experience, joints that were torqued in a rush and never re-checked are the most common cause of a single warm spot on an otherwise cool busbar chamber. We torque joints to the approved values, record them, and thermal-scan the busbar chamber during the heat-up part of FAT rather than relying on a visual check.

Therefore thermal design and busbar quality are connected.

Breaker Heat

Large ACBs and MCCBs can contribute meaningful losses.

At high current:

I²R losses increase.

The manufacturer's power-dissipation data should be considered in detailed thermal calculations.

This is particularly important in compact high-current switchboards.

APFC Detuned Reactors

Detuned APFC panels can have significant thermal loading because reactors dissipate heat.

Therefore:

• Reactor spacing
• Ventilation
• Thermostat
• Thermal protection
• Enclosure volume

become important.

A detuned APFC panel should not simply reuse the enclosure of a normal capacitor bank with reactors added wherever space remains.

Control Transformer Heat

Control transformers dissipate:

• Core losses
• Copper losses

Even when panel control load seems small, a transformer can contribute persistent heat.

Use manufacturer loss information where available.

Soft Starter Heat

During starting, thyristors dissipate heat.

After bypass, continuous losses can reduce significantly depending on design.

Therefore heat calculation should reflect the actual:

• start duration
• starts/hour
• bypass arrangement

rather than assuming soft starter behaves like a continuously loaded VFD.

Ambient Inside the Panel Is Not Room Ambient

Suppose room ambient:

40°C

That does not mean every component sees 40°C.

Inside the enclosure:

• Top section may be 50°C+
• VFD exhaust area may be hotter
• Control section may differ

Therefore use:

local component ambient

where required.

Hot spots matter.

Temperature Sensors

For critical panels, temperature monitoring can provide valuable operational information.

Possible locations:

• Busbar compartment
• VFD compartment
• Reactor section
• Top of enclosure

But sensors do not fix poor thermal design.

They only tell you the condition.

Thermostat Control

Fans are often controlled using:

Thermostat

This avoids running fans continuously where not required.

But switching points should reflect:

• Component limits
• Expected ambient
• Hysteresis
• Required airflow

No universal thermostat setpoint suits every panel.

Redundant Fans

For process-critical panels, designers may evaluate:

• Multiple fans
• Fan-failure alarm
• N+1 airflow capacity

depending on risk.

This is not necessary for every panel.

Reliability requirement should drive it.

Fan Failure Detection

Possible methods:

• Airflow switch
• Fan auxiliary signal
• Current monitoring
• Temperature high alarm

For a critical VFD panel, a fan failure can be detected before the drive reaches overtemperature shutdown.

Condensation

Cooling is not the only thermal problem.

Cold/humid environments can create:

Condensation

Possible mitigation:

• Anti-condensation heaters
• Hygrostat
• Controlled enclosure temperature
• Proper sealing

This is particularly relevant during shutdown periods when internal equipment is not generating heat.

Water-treatment and effluent-plant panels are where we see this most. A panel that runs warm and dry all week sits idle over a monsoon weekend, the enclosure cools to dew point overnight, and Monday morning starts with low insulation-resistance readings or a nuisance earth-fault trip. A modest 50 to 100 W anti-condensation heater on a hygrostat costs a fraction of one such call-out. Our recommendation: for outdoor and washdown-area panels, treat the heater and hygrostat as part of the base scope rather than an option — and check during FAT that the heater circuit is fed upstream of the main switch, otherwise it stops working exactly when the panel is shut down and needs it.

Heat Calculation Example — Why Ambient Changes Everything

Assume:

Panel heat loss:

2000 W

Case A

Ambient = 30°C

Max internal = 50°C

ΔT = 20 K

Required simplified airflow is much lower.

Case B

Ambient = 40°C

Max internal = 50°C

ΔT = 10 K

Required airflow approximately doubles.

Case C

Ambient = 50°C

Max internal = 50°C

ΔT = 0 K

The ventilation formula no longer provides a viable cooling solution because ambient air offers no temperature difference.

This demonstrates:

Ambient temperature is one of the most important panel design inputs.

Why Oversized Fans Are Not Always Good

Too much airflow can create:

• Excess dust intake
• Noise
• Larger filter size
• Higher power consumption
• Uncontrolled pressure
• Short-circuit air path

Correct airflow is better than simply using the largest fan that fits.

Positive Pressure

Filtered inlet fans can be arranged to create slight positive pressure inside an enclosure.

This can help reduce uncontrolled dust ingress through small gaps.

But the design must balance:

• Inlet airflow
• Exhaust area
• Filter loading
• Enclosure protection

Do not assume any fan arrangement automatically preserves the original IP rating.

Thermal Management Tools

Several major manufacturers provide dedicated tools rather than relying solely on hand calculations.

These tools demonstrate an important engineering principle:

Thermal selection should be calculated from actual panel conditions—not selected only by experience or enclosure volume.

Information Required for Panel Thermal Design

Environment

• Maximum ambient
• Minimum ambient
• Indoor/outdoor
• Altitude
• Humidity
• Dust
• Solar exposure

Enclosure

• Dimensions
• Material
• IP rating
• Wall-mounted/floor-standing
• Adjacent panels
• Free-standing/bayed
• Available surface area

Components

• VFD heat loss
• Breaker loss
• Reactor loss
• Transformer loss
• Power supply loss
• Other electronic losses

Operating Conditions

• Simultaneous loading
• Duty cycle
• Starts/hour
• Production profile

Target

• Maximum internal temperature
• Critical component lowest temperature limit

Only after this should the cooling method be finalized.

Choosing the Cooling Method

Natural Convection

Good when:

• Heat load low
• Ambient sufficiently below internal limit
• Enclosure surface area adequate

Filter Fan

Good when:

• Ambient is cooler than panel target
• Environment allows filtered outside air
• Moderate heat load

Air-to-Air Heat Exchanger

Good when:

• Closed air circuit desired
• Ambient cooler than inside
• Contamination high

Panel Air Conditioner

Good when:

• Ambient may approach/exceed internal target
• Heat load high
• Sealed panel required
• Sensitive electronics present

Other Cooling Technologies

For specialized high-density applications:

• Air-to-water heat exchangers
• Liquid cooling
• External heat sinks

may be evaluated.

Common Panel Cooling Mistakes

Mistake 1 — Fan Selected From Panel Size

Cooling requirement comes primarily from heat load + environment.

Mistake 2 — Ignoring VFD Losses

Large drives can dominate thermal load.

Mistake 3 — Using Free-Air Fan Rating as Installed Airflow

Filters and restrictions reduce airflow.

Mistake 4 — Trying to Cool Below Ambient With Fans

Ventilation cannot provide refrigeration.

Mistake 5 — Increasing IP Without Thermal Review

Sealed enclosure changes heat rejection.

Mistake 6 — Ignoring Reactor Heat

Especially detuned APFC and harmonic filters.

Mistake 7 — All Heat Sources Placed Together

Creates local hot spots.

Mistake 8 — No Filter Maintenance Access

Dirty filters destroy actual airflow.

Mistake 9 — FAT Fan Test Considered Full Temperature-Rise Verification

Fan rotation/function does not prove full-load thermal capability.

Mistake 10 — Generic “45°C Suitable” Label Without Design Evidence

Complete assembly conditions matter.

Relevant Standards

IEC 61439-1:2020 provides the general LV assembly requirements and includes temperature-rise verification in the design-verification framework.

IEC 61439-2:2020 applies to power switchgear and controlgear assemblies within its scope.

IEC TR 60890:2022 provides a calculation method for internal air temperature rise for applicable enclosed LV assemblies/sections without forced ventilation.

For Indian projects, BIS lists IS/IEC 61439 Part 1:2020 and Part 2:2020 as the current Indian adoptions.

Panel Cooling FAT Checklist

Construction

Verify:

• Fan size/type
• Inlet location
• Exhaust location
• Filters
• Louvers
• AC unit
• Heat exchanger
• Internal airflow path

Fan Operation

Verify:

• Correct direction
• Thermostat switching
• Manual test
• Alarm where required

Temperature Control

Verify:

• Thermostat
• Hygrostat
• High-temperature alarm
• Heater where applicable

Cooling Unit

Verify:

• Start/stop
• Setpoint
• Alarm
• Condensate
• Power supply

PLC / SCADA

Verify required:

• High panel temperature
• Fan failure
• AC fault
• Temperature indication

Documentation

Record:

• Component heat losses
• Cooling calculations
• Selected fan/AC ratings
• Ambient design basis
• Setpoints

But remember:

Routine FAT of fans and thermostats does not replace applicable IEC 61439 temperature-rise design verification.

How Wisdom Techno Solutions Approaches Thermal Design

For WTS panels, thermal design should begin before enclosure dimensions are frozen.

Important inputs include:

• Equipment make/model
• Manufacturer heat-loss data
• Maximum ambient
• IP requirement
• Simultaneous loading
• VFD/reactor arrangement
• Component temperature limits
• Installation location

Depending on project requirements, we engineer panel layouts incorporating:

• Natural ventilation
• Filter fans
• Exhaust systems
• Internal circulation
• Thermostats
• Temperature alarms
• Panel air conditioning
• Heat-management segregation

The cooling approach should form part of the overall panel engineering—not an accessory added after the GA is complete.

Wisdom Techno Solutions is a licensed partner for three design-verified switchgear platforms: Rittal Ri4Power (Rittal Solutions Partner since 2021 — the Ri4Power system carries Intertek ASTA design verification to IEC 61439-1 and -2 Edition 3, with copper and aluminium busbar systems up to 6300 A), C&S CX (Licensed Partner since 2023, up to Form 4B Type II) and Siemens SIEPAN Elite/8PU (IEC 61439 Solutions Partner since 2024). We build to each system's verified configuration and routine-verify every assembly in-house at our Vadodara, Gujarat facility, for industrial, EPC and infrastructure projects across India. That places the temperature-rise verification basis inside a verified design envelope.

The objective is:

Keep every component within its allowable operating temperature under the actual worst credible operating condition while maintaining the required environmental protection.

Conclusion

Panel cooling begins with a simple question:

How many watts of heat are being generated inside the enclosure?

Then ask:

• What is maximum ambient?
• What internal temperature is acceptable?
• How much heat can enclosure surfaces reject?
• Can outside air be used?
• What IP rating is required?
• Is dust severe?
• Are VFDs/reactors installed?
• Is altitude significant?

A simplified ventilation calculation can estimate airflow from heat loss, air properties and the allowable internal-to-ambient temperature difference.

But final thermal engineering should use:

• Actual component-loss data
• Real enclosure geometry
• Environmental conditions
• Applicable IEC verification
• Appropriate manufacturer calculation methods

The key lesson is:

An electrical panel is not thermally correct because all components physically fit inside it.

Correct thermal design means they can operate at the required load, in the required ambient, inside the required IP enclosure, without exceeding their permitted temperature.

That distinction has a direct impact on:

reliability, equipment life and plant uptime.

Related Guides

• Busbar sizing for LT panels
• Normal APFC vs detuned APFC
• APFC panel sizing and kVAr calculation
• Form 1/2/3/4a/4b internal separation
• Product page: PMCC panel

Frequently Asked Questions

How do I calculate electrical panel heat dissipation?

Sum the power losses in watts of every heat-producing component — drives, breakers, reactors, control transformers, power supplies, busbars and connections — using manufacturer heat-loss data rather than assumed efficiency figures. That total, Ptotal, is the heat the enclosure must reject. Then compare it against what the enclosure can remove at the maximum ambient temperature at the installation point, keeping every component within its permitted temperature. A panel with 2 × 75 kW drives can easily reach 3 to 4 kW of internal loss, which is a heating load, not a rounding error.

How is required fan airflow calculated?

A commonly published simplified method is:

Q = P / [ρ × c × (Tin − Tamb)]

where P is the internal heat load, ρ and c are the density and specific heat of air, Tin is the maximum permitted internal temperature and Tamb the maximum cooling-air temperature. Using approximate hot-air values of ρ ≈ 1.1 kg/m³ and c ≈ 1 kJ/kg·K, a 2 kW panel at 40 °C ambient with a 50 °C internal limit needs roughly 0.18 m³/s, or about 655 m³/h. That figure is a theoretical minimum: catalogue fan airflow is usually quoted in free air, so filters, grilles and internal restrictions must be allowed for before a fan is selected.

Can a fan cool a panel below ambient temperature?

No. A ventilation fan only exchanges hot enclosure air for ambient air, so the best it can achieve is an internal temperature approaching ambient — it cannot refrigerate. If the site ambient is 50 °C and the components need 50 °C or less, there is no temperature difference left to work with and a bigger fan changes nothing. That situation requires panel air conditioning, air-to-water cooling, a conditioned electrical room, or reselection and derating of the components.

When is panel AC required?

Panel air conditioning becomes necessary when the enclosure has to be held below the surrounding air temperature — typically where the maximum ambient approaches or exceeds the permitted internal temperature, where the heat load is high, or where the panel must stay sealed against dust and moisture. It is the only common option that actually refrigerates; fans and air-to-air heat exchangers can only work with a favourable ambient. The trade-offs are capital cost, running power, condensate drainage and regular coil and filter cleaning, so the unit should be sized from the calculated heat load rather than chosen by enclosure size.

Does IP55 affect heat dissipation?

It can. More sealed enclosures restrict uncontrolled air exchange, so thermal performance should be reviewed when IP requirements change.

Why do VFD panels need more cooling?

A drive converts power electronically all the time it is running, so its losses are continuous rather than momentary. Even an efficient drive at a large rating can dissipate on the order of 1.5 kW, so two such drives put roughly 3 kW into the enclosure before input reactors, breakers, control transformers and power supplies are counted. Reactors and filters associated with the drive add further heat in the same box. This is why a compact sealed enclosure with several large drives inside is one of the most demanding thermal cases in LT panel design.

Should I use VFD efficiency to estimate heat?

No — use the manufacturer's declared heat-loss or power-dissipation figure wherever it is available. An assumed loss such as "5% of rated kW" can be well off the mark, because efficiency varies substantially between models and, for the same drive, between operating points and switching frequencies. Working from a percentage tends to overstate losses on modern drives and understate them once filters and reactors are included, so the enclosure ends up sized against a number that describes no real equipment.

What is IEC TR 60890?

IEC TR 60890:2022 is a technical report describing a method of temperature-rise verification of low-voltage switchgear and controlgear assemblies by calculation. It gives a way of estimating internal air temperature rise for enclosed or partitioned assembly sections, and it is primarily applicable to sections without forced ventilation. That limitation matters in practice: a spreadsheet calculation for a fan-cooled enclosure is a useful engineering estimate, but it is not the same thing as applying IEC TR 60890 within its stated scope.

Does IEC 61439 require temperature-rise verification?

Yes. Temperature rise is one of the design-verification characteristics within the IEC 61439-1:2020 assembly framework, and IEC 61439-2:2020 applies that framework to power switchgear and controlgear assemblies. The verification concerns the loaded assembly as a whole, so it takes in busbar and connection losses, installed devices, the enclosure and the component arrangement — not just the size of the busbar. This is why a claimed rated current has to be supported by temperature-rise evidence for the assembly rather than by component ratings alone.

Does running the fan during FAT prove temperature-rise compliance?

No. Functional FAT of the cooling system and IEC assembly temperature-rise verification are different activities.

Is larger enclosure always enough to solve heating?

Not automatically. More surface area and spacing can help, but the enclosure must still dissipate the total generated heat under actual ambient conditions.

Does altitude affect cooling?

Yes. Air density and cooling performance can change with altitude; current enclosure thermal-planning tools include altitude as a calculation input for exactly this reason.

What data should be provided for panel cooling design?

Provide the environment first: maximum and minimum ambient at the actual panel location, indoor or outdoor, altitude, humidity, dust level and solar exposure. Then the enclosure data — dimensions, material, IP requirement, wall-mounted or floor-standing, and whether it is free-standing or bayed between other panels, since a bayed panel loses two dissipating surfaces. Then the component heat-loss figures for drives, breakers, reactors, transformers and power supplies, together with simultaneous loading, duty cycle and starts per hour. Finally state the maximum permitted internal temperature and the limit of the most temperature-sensitive component, because that is the figure the whole cooling design is built around.