Panel Layout, Heat and Enclosures
Layout zones, enclosure ratings, heat dissipation and fan or air-conditioner sizing, short-circuit rating and labeling.
Layout zones
A good panel layout puts power at one side, control electronics at the other, wire ducts between and field terminals at the edge nearest the cable entries. The aim is short wires, separated noisy and sensitive circuits, room for air, and easy access for the person who has to find a fault at 2 am.
- Heat rises. Put the parts that make the most heat (drives, power supplies, resistors) at the top with clear space above and below (the maker states the clearances), and the temperature-sensitive electronics (PLC, network) lower down and away from them.
- Separate noisy and sensitive wiring (see Grounding, Shielding and Noise): drives and contactors on one side, analog and network on the other, and signal ducts on separate routes.
- Keep terminals together by function and on the cable-entry side, with a spare row, and group the signals by type and voltage.
- Mount everything on a bare, galvanized or zinc-plated plate with metal-to-metal contact for earthing (see Grounding, Shielding and Noise), and run an earth bar along its base.
- Keep the door light: operator devices on the door with flexible, well-supported wiring; heavy items stay on the plate. A door can carry only a few kilograms: check the enclosure maker’s limit (6 kg is typical for a medium door).
- Put the isolator on the door (with the interlock) or on the side and make sure it can be locked.
- Lay it out on paper or CAD first; a layout drawing is part of the documentation (see Documentation, Handover and Lifecycle).
Space on the mounting plate
Worked example: will it fit?
A 800 × 600 mm enclosure has a plate of about 700 × 500 mm = 0.35 m². If the devices and their wire ducts occupy 55 % of the plate (0.19 m²) and you want 25 % free for air, wiring space and later additions, you need a plate of 0.26 m²: it fits. Do this check before ordering the enclosure: a panel that is too full is hot, hard to wire and hard to maintain.
Heat dissipation
Every component wastes some power as heat inside the panel. Add the dissipation of all the components from their datasheets (use the figures at the actual load, not the nameplate). The enclosure can lose heat through its surface to the air outside, depending on its area, its material and finish, and the air movement.
Worked example: the heat inside a panel
| Component | Heat |
|---|---|
| Drive, 4 kW (about 3 % losses) | 120 W |
| Drive, 1.5 kW | 55 W |
| 24 V supply, 10 A at 92 % efficiency | 21 W |
| PLC, I/O and network switch | 25 W |
| Contactors, relays and breakers | 28 W |
| Line reactor and filter | 40 W |
| Terminals, wiring and others | 11 W |
| Total | 300 W |
Together the components dissipate 300 W. This is a rough figure: use the manufacturers’ values, and note that drive losses rise with the carrier frequency and the load.
Will natural cooling do?
ΔT = P ÷ (k × A) (k ≈ 5.5 W/m²K for painted sheet steel; A = effective surface area)
Worked example: a sealed 800 × 600 × 250 mm enclosure
- The effective surface of a free-standing enclosure against a wall is about A = 1.8 H (W + D) + 1.4 W D = 1.8 × 0.8 × (0.6 + 0.25) + 1.4 × 0.6 × 0.25 = 1.43 m² (a simplified form of the IEC 60890 method).
- With 300 W inside, the rise is 300 ÷ (5.5 × 1.43) = 38.0 K. In a 35 °C shop, the air inside reaches 73 °C, above the 45 °C inside that most devices can take.
- The enclosure can dissipate only 5.5 × 1.43 × (45 − 35) = 79 W for a 10 K rise: the 221 W beyond that must be removed by other means.
- A larger enclosure of 1 200 × 800 × 300 mm (A = 2.71 m²) would run at 20.1 K above the room, 55 °C inside: still too hot. A bigger box is the simplest cure but not always cheap.
Fans and filters
V (m³/h) = 3.1 × P ÷ ΔT (P in W, ΔT in K)
Worked example: a filter fan
- To remove the whole 300 W with a 10 K rise: V = 3.1 × 300 ÷ 10 = 93 m³/h. If the enclosure itself already dissipates 79 W, the fan needs to deal with only 221 W: 69 m³/h.
- A filter and its grille can halve the airflow the fan gives in free air, so choose a fan with a free-air rating of about 186 m³/h. A fan with an outlet filter must be matched to the pressure drop (the curve is in the datasheet).
- A fan brings in the outside air, so it works only where the air is clean and cooler than the target; filters clog and need changing on a schedule, and the enclosure rating falls to about IP54.
- Fans fail: fit a thermostat and a temperature alarm to the PLC, so that failure is noticed before the drives trip (see HMI, Alarms, Data and Cybersecurity).
Air conditioners and heat exchangers
Where the outside air is dirty, wet or hot, a closed loop is needed: an air-to-air heat exchanger (works only if the outside is cooler than the inside), an air conditioner (a refrigeration unit that can cool below ambient), or a liquid cooling loop for big drives.
Worked example: sizing a cooler
- Holding the inside at 35 °C in a 35 °C shop, the walls pass no heat either way, so the cooler must remove all 300 W. With a 20 % margin: 360 W of cooling.
- In a hot plant at 45 °C outside the enclosure also gains heat through its walls: 5.5 × 1.43 × (45 − 35) = 79 W, on top of the internal 300 W: about 379 W, or 455 W with margin. Size the cooler for the worst ambient, and add the solar load for an enclosure in the sun.
- Set the air conditioner’s thermostat so that condensation does not form (about 35 °C or a few degrees above the outside dew point), and provide a drain.
- Keep the door closed: a door left open defeats any cooling and lets in dust and moisture.
Why temperature matters
Worked example: aging
- A common rule for electrolytic capacitors in power supplies and drives is that the life halves for every 10 °C rise. A capacitor rated 100 000 hours at 40 °C lasts 10 000 hours at 73 °C inside the panel (a factor of 0.10), about 1.2 years of continuous running.
- Many components are derated above 40 °C (a drive may lose 2 % of its current for each degree above): 66 % at 73 °C inside.
- Condensation and humidity cause corrosion and tracking: a small heater and a thermostat keep the inside above the dew point in a cold or damp plant.
Enclosure ratings
| IP code | Protection | Typical use |
|---|---|---|
| IP20 | Fingers; no dust or water protection | Inside a closed panel only |
| IP54 | Dust-protected; splashing water | Dry factory floors |
| IP55 | Dust-protected; water jets | General industry, outdoors under cover |
| IP65 | Dust-tight; water jets | Washdown areas, dusty plants |
| IP66 | Dust-tight; powerful water jets | Heavy washdown |
| IP67 | Dust-tight; temporary immersion | Field boxes, sensors |
| IP69K | Dust-tight; high pressure, hot water | Food and beverage hygienic areas |
- IP codes (IEC 60529): the first digit is protection against solids, the second against water. NEMA types (North America) also cover corrosion and ice: type 12 is for indoor dust and drips, 4 and 4X for washdown, 4X for corrosion.
- Stainless steel (304 or 316) for food, pharma and corrosive environments; painted steel for general use; polycarbonate and GRP for small field boxes and corrosive areas.
- Every hole lowers the rating: use rated glands and plugs, gaskets in good condition and the right mounting of fans and coolers.
- Hazardous areas need certified equipment (ATEX, IECEx, Class/Division) and installation rules of their own.
- Consider maintenance access: a front door that opens fully, space to work, a place to put the laptop, a light and a socket.
Building and labeling the panel
- Follow a panel standard for the assembly (IEC 61439, UL 508A): it covers clearances, wiring, temperature rise, short-circuit rating, marking and testing.
- Mark the nameplate with the supplier, the supply voltage, phases, frequency, full-load current of the largest motor, the short-circuit current rating, the drawing number and the year (see Power Distribution and the Control Supply).
- Fit a pocket for the schematics in the door, or a QR code that links to the current set.
- Label every device with the reference on the schematic, in a place that is visible with the door open, and every terminal block and wire.
- Weigh and lift: note the weight of the panel (about 18 kg for a small wall box, hundreds for a floor-standing one) and fit lifting eyes; check the wall or the frame it hangs on.
- Clean it before it leaves the workshop (no wire offcuts, swarf or dust) and give it a final inspection against the drawings (see Testing, Commissioning and Acceptance).
Related
- System Integration: the overview of this guide.
- Power Distribution and the Control Supply: the devices that go into the panel and their heat.
- Grounding, Shielding and Noise: earthing, shielding and separation inside the panel.
- Documentation, Handover and Lifecycle: the layout drawing and the bill of materials.
FAQ
How do I know if my panel will overheat?
Add the heat dissipated by all the components, and compare it with what the enclosure can lose to the air: P = k A ΔT, with k about 5.5 W/m²K and A the effective surface. If the components make more heat, add a fan, a heat exchanger, an air conditioner or a larger enclosure.
How much free space should I leave on the plate?
About 25 % free for air, extra wiring and later additions, in addition to the clearances the device makers require around drives and power supplies.
Fan or air conditioner?
A filter fan is cheap and works only where the outside air is clean and cooler than the target inside temperature. An air conditioner works in hot, dirty or wet places and keeps the enclosure sealed, at a higher cost and with its own maintenance.
What IP rating do I need?
IP54 or IP55 for a dry factory, IP65 or IP66 for washdown or dust, IP69K for hot high-pressure cleaning, and stainless steel for corrosive or hygienic areas. Remember that fans and openings reduce the rating.
References
- IEC 61439-1 and -2, Low-voltage switchgear and controlgear assemblies; IEC TR 60890 (temperature-rise verification by calculation); IEC 60529 (IP code); UL 508A and NEMA 250 (enclosure types).
- Rittal, Hoffman, Schneider and others, Climate control and enclosure sizing guides (the formulae for k, effective area and airflow).
- Drive, power-supply and PLC manufacturers’ installation manuals for losses, clearances and derating.
Last reviewed: October 2026. Losses, areas and temperatures are typical and illustrative: use the datasheets and the enclosure maker’s sizing tool.