Symptom
A drive trips on over-temperature or reduces its output in hot weather; a controller faults or an HMI goes blank in the afternoon; the enclosure is hot to the touch; components are discolored or their labels browned; a fan runs continuously; an internal temperature alarm is active.
The short answer
Panel Overheating
A panel overheats when the heat its components produce exceeds what the enclosure can shed at the ambient it sits in, and the causes are an enclosure too small or sealed for its load, a load that grew when drives were added, a cooling fan or filter or air conditioner that failed or clogged, an ambient that rose from sun or a hot room, or a component such as a drive at high carrier frequency dissipating more than expected. Measure the temperature inside against the ambient, at the hottest time of day with the drives running, and compare the rise with the heat calculation; then fix in order: restore the cooling that exists, reduce the sources, shade and ventilate the location, and add cooling sized from the calculation when the enclosure cannot shed the load.
Key points
- Measure inside against ambient at the worst time of day; the rise is what the enclosure is failing to shed.
- Compare with the heat calculation; if there is none, do one from the bill of material.
- Restore what exists first: filters, fans, cooling units, thermostats, door gaskets.
- Reduce the source: drive carrier frequency, heaters left on, loads that can move out.
- Add cooling sized from the calculation, of a type that keeps the enclosure rating.
Possible causes and what to check
| Possible cause | What to check |
|---|---|
| Enclosure undersized for the dissipation | Sum the component heat from the bill of material and compare with the enclosure surface and the ambient; a sealed enclosure sheds only a few watts per square foot for a modest rise. |
| Loads added since the enclosure was sized | A drive or a power supply added without a new heat calculation. Compare the current contents with the original drawing. |
| Filter clogged or fan failed | Fan running but no airflow at the outlet; the filter mat dark with dust; the fan seized. Replace the filter; test the fan. |
| Air conditioner or heat exchanger failed or iced | Unit running with no cooling, or tripped; condenser filter blocked; refrigerant lost. Read the unit indicators and clean the condenser. |
| Thermostat set wrong or failed | The fan or the cooler does not start at the intended temperature; a heater thermostat left on in summer. Check the settings and test the switch. |
| Ambient too high: sun, a hot room, a roof | Enclosure in direct sun or in a room with the drives and the blowers. Measure the surface temperature and the room; a shade or a relocation. |
| Drive at high carrier frequency | Drive losses rise with carrier frequency; lower it within the manual range and re-measure. |
| Vents blocked or the door gasket sealing a vented enclosure | Vents covered by a label, a nearby wall, or a new cabinet; airflow path obstructed. Clear the path. |
| Component failing and running hot | One component far hotter than its neighbors on a thermal image: a contactor with a bad magnet, a power supply with a failing capacitor, a loose termination. |
Measure
- 1
Inside and outside
A thermometer or a logger inside the enclosure at the top, where the heat collects, and one outside in the shade, through the hottest afternoon with the drives running. The difference is the rise.
- 2
Thermal image
The components with the door open briefly: the ones that stand out are the sources or the failures.
- 3
The calculation
Watts from the bill of material, the enclosure surface area, and the ambient, using the enclosure manufacturer method. The predicted rise against the measured rise says whether the enclosure was ever adequate.
- 4
The cooling
What was designed: none, fan and filter, heat exchanger, air conditioner, and whether it is working as designed.
What the timing says
| Pattern | Likely cause |
|---|---|
| Hot only in the afternoon in summer | Ambient and sun; the enclosure has no margin |
| Hot whenever the drives run | Drive dissipation exceeds the enclosure; carrier frequency; a cooling unit sized for less |
| Hot since a modification | Loads added without a heat calculation |
| Gradually hotter over months | Filter clogging; fan or condenser degrading |
| Suddenly hot | Fan, cooling unit, or thermostat failed; a component failing |
| Hot in winter | Heater thermostat set too high or failed on |
Fixes in order
- Restore: replace the filter, the fan, or the cooling unit; set the thermostats; clean the condenser; clear the vents.
- Reduce: lower the drive carrier frequency; turn off the heater in summer; move a load that does not need to be inside.
- Shade and ventilate: a sunshade over an outdoor enclosure; ventilation for the room; move the enclosure off the drive wall.
- Add cooling: a fan and filter where the rating allows; a heat exchanger or an air conditioner sized from the calculation where the enclosure must stay sealed.
- Replace the enclosure: larger, or a separate enclosure for the drives, when the calculation says nothing else will do.
Why it matters
Electronics age with temperature: capacitor life halves for every ten degrees of rise, a drive derates its output above its rated ambient, and a controller that faults at the peak of the afternoon has been stressed every afternoon before. A panel that runs twenty degrees above ambient in summer is one whose power supplies and drives fail years early, and the failures arrive in the hottest week of the year when the plant can least afford them.
Frequently asked questions
- Can I leave the door open on hot days?
- It loses the enclosure rating and admits dust, insects, and hands, and it is the reason the panel is full of dirt. It is a temporary measure while the real fix is ordered, not an operating practice. A panel that needs its door open has a heat problem to solve.
- How hot is too hot inside?
- The rating of the components: most controllers and supplies are rated to 55 or 60 degrees Celsius at the component, drives to 40 or 50 with derating above, and the enclosure air near the top is where the reading is taken. A rise of more than 15 or 20 degrees above ambient in a sealed enclosure is a sign the calculation was never done.
- Would a bigger fan help?
- Only if the enclosure is vented and the ambient is lower than the target inside; a fan cannot cool below the outside air. In a sealed enclosure a fan only circulates; the heat has to leave through the walls or a heat exchanger.
- The drive in the panel is fine but the controller faults. Why?
- The drive heats the air and the controller above it takes the heat; drives are rated hotter than controllers. Move the controller lower or to another enclosure, or cool the enclosure. The layout drawing convention of power at the top and controls below exists partly for this reason.
Related topics
- Enclosure Heat CalculationsEstimating the temperature inside a control panel from the power its contents dissipate and the surface that carries it out, what to do when the answer is too hot, and why drives change everything.
- Enclosure SelectionChoosing the box: NEMA and UL 50 type ratings, materials for corrosive and outdoor sites, sizing for heat and wire bending space, and the details at the conduit entries and the door that decide whether the rating survives installation.
- Component LayoutArranging a panel so it is safe to work in, cool enough to run, quiet enough for its signals, and possible to modify: power and control separation, heat, wireways, terminals, and the working space rules.
- Panel LayoutsThe drawing of what goes where inside a control panel: enclosure, back plate with every component to scale and keyed to the bill of material, wireways, terminals, door devices, and entries. The conventions, the required spacings, and the checks.
- Variable Frequency Drives in Pump PanelsWhat a drive adds to a pump panel and what it costs: speed control, soft start, reduced inrush, and diagnostics against heat, harmonics, cable and motor stress, bypass, and the minimum speed below which a pump does no work.
- Power Supply FailureA 24 volt DC supply whose output is gone, low, cycling, or noisy: an overload that has put it into current limit, a supply killed by heat and age, input voltage out of range, or surge damage. One test tells an overloaded supply from a dead one.
Direct contact
Have a controls question?
Reach Eric Sullivan directly about anything on this site, a controls or automation topic, or one of his personal projects.