learn · South Africa
Panel Layout Fundamentals: Space, Heat and IP Ratings
Learn panel layout fundamentals with clearance, terminal-space and heat-loss examples, IP-rating limits and South African electrical training questions.
Panel layout fundamentals connect the component schedule, installation instructions, wiring routes, environmental conditions and maintenance access. A neat drawing is useful, but a component fitting on the backplate does not prove that it has adequate cooling, service space or electrical separation. Those requirements need their own evidence.
This guide uses fictional geometry and heat-balance worksheets to explain the decisions. Their dimensions and assumptions are not a construction drawing for a real panel. The illustrations are conceptual learning assets, not approved schematics or a panel-design simulation. For a broader learning route, compare industrial electrical training in South Africa.
Begin with a design brief and an evidence register
Before placing a PLC, establish where the enclosure will be installed and what it must contain. Record the intended equipment, supply arrangement, operating duty, ambient conditions, cable entries, access restrictions and future expansion requirement. Separate confirmed values from assumptions that still need a manufacturer's document or a site measurement.
A useful component schedule includes the exact catalogue number, quantity, physical dimensions, mounting orientation, required free space, connection location, loss data and environmental limits. Record the document revision beside each value. “CompactLogix” or “24 V power supply” is not specific enough to identify every installation requirement.
| Requirement | Evidence to obtain | Why a generic assumption is insufficient |
|---|---|---|
| Usable mounting space | Enclosure and backplate drawings | External dimensions include space unavailable for components |
| Device clearance | Matching installation instructions | Requirements can depend on orientation and temperature |
| Heat dissipation | Loss data at the intended operating point | Electrical output power is not automatically enclosure heat |
| Cable routing | Cable, connector and equipment instructions | Bend radius and shield arrangements vary |
| Environmental suitability | Enclosure and accessory declarations | An IP code does not describe every exposure |
| Service access | Removal procedure and access review | A body outline omits tools, plugs and moving parts |
These records support a reviewable decision. If a value is unknown, make that gap visible. Substituting a plausible-looking number can make the drawing appear finished while leaving the controlling constraint unresolved.
External enclosure size is not usable backplate area
Consider a fictional enclosure with external dimensions of 600 mm wide, 800 mm high and 250 mm deep. Those numbers do not establish the backplate dimensions, mounting offsets, door equipment depth or gland-plate area. For this worksheet only, declare a usable backplate rectangle of 520 × 700 mm.
Reserve a 40 mm vertical wireway on each side and a 10 mm gap between each wireway and the central equipment bay. The bay width is therefore 520 − 40 − 40 − 10 − 10 = 420 mm. A drawing that uses the full external 600 mm as available equipment width would overstate this declared bay by 180 mm.
Use a consistent coordinate system: x increases from the backplate's left edge and y increases downward from its top edge. The left wireway occupies x=0–40 mm. The equipment bay occupies x=50–470 mm. The right wireway occupies x=480–520 mm. The two intervening 10 mm strips are reserved gaps.
This is a two-dimensional planning model. It omits screw locations, cable depth, door hardware and the enclosure's actual mounting system. It is useful for checking arithmetic and communicating reserved areas, but it cannot prove that a real assembly is buildable.
Worked clearance-envelope check: a body can fit while its space does not
Define a fictional controller assembly body measuring 220 × 100 mm. For this exercise, reserve 50 mm on all four sides, producing a 320 × 200 mm envelope. Also define a fictional power-supply body measuring 75 × 125 mm, with 20 mm reserved on each side, producing a 115 × 165 mm envelope.
These clearances are deliberately declared worksheet inputs. They are not attributed to either a specific PLC or a specific power supply. In the exercise, reserved envelopes may not overlap. A real design must interpret the actual manufacturer's clearance wording rather than assuming every clearance zone behaves like our rectangles.
Try to put the two envelopes side by side with a further 15 mm gap. Their required width is 320 + 15 + 115 = 450 mm. The equipment bay is only 420 mm wide, so that arrangement exceeds the available width by 30 mm. Looking only at the two body widths would have hidden the problem.
| Arrangement | Required size in the relevant direction | Available size | Worksheet result |
|---|---|---|---|
| Controller envelope alone | 320 mm wide | 420 mm | Fits across the bay |
| Controller and PSU side by side | 450 mm wide | 420 mm | Exceeds width by 30 mm |
| Controller above PSU with a 20 mm gap | 385 mm high | 700 mm | Fits vertically in this simplified check |
For the vertical option, place the controller envelope at x=50–370, y=50–250 mm and the PSU envelope at x=50–165, y=270–435 mm. Both lie inside the declared equipment bay and backplate height, with a 20 mm vertical gap. This establishes a geometric alternative, not a cooling recommendation or a complete layout. Other equipment, wireways and access zones still need allocation.
The important habit is to draw the required envelope as well as the body. Keep separate layers for physical components, reserved space and routes so a reviewer can see which constraint a proposed move affects.
Use the exact device's clearance and mounting instructions
Real clearance values can differ substantially from the worksheet. Rockwell's CompactLogix 5380 installation instructions, 5069-IN013K, describe horizontal DIN-rail mounting and temperature-dependent minimum space around the system. The cited document gives 50.8 mm at 55 °C and 101.6 mm at 60 °C between the system and enclosure walls, wireways or adjacent equipment.
Those figures are an example of why the model and operating conditions matter. They are not a blanket clearance for every CompactLogix family, every installation temperature or every associated device. Read the remaining installation conditions and the applicable component documents together.
Also distinguish ventilation space from removal access. A required free-air zone does not necessarily include the space needed to release a latch, unplug a connector, operate a screwdriver or withdraw a module. Review the removal sequence with the door and adjacent equipment included.
Extra clearance does not translate into a guaranteed number of degrees of temperature margin. A 70 mm gap cannot simply be described as absorbing a 10 °C rise in room temperature. Thermal performance depends on the equipment losses, airflow and surrounding conditions.
Count terminals, accessories and spare space explicitly
Terminal planning is another place where a plausible body total can conceal a fit problem. Suppose a fictional row contains 60 terminals, each 5.2 mm wide. The terminal bodies occupy 60 × 5.2 = 312 mm. That is not the finished rail allocation.
Add two 8 mm end stops, two 2 mm end plates and a specified 20 mm spare allowance. The total becomes 312 + 16 + 4 + 20 = 352 mm. If the available rail length is 340 mm, the row is short of space by 12 mm.
Removing the spare allowance would reduce the total to 332 mm, but that would change the brief. Do not silently delete an expansion requirement to make a layout pass. Either revise the requirement with its owner or change the arrangement.
If the same sixty terminals are split into two rows of thirty, each row needs 156 + 16 + 4 + 20 = 196 mm under the same per-row accessory and spare assumptions. Both rows together reserve 392 mm of rail length. Splitting the row changes the accessory count and also requires a second vertical allocation; it is not just dividing 352 by two.
Keep terminal functions, wire identification and test access visible. For learning about how signal meaning connects with those physical terminations, use analog signal fundamentals. A terminal count alone does not establish an appropriate circuit or segregation plan.
Heat-loss worksheet: distinguish power delivered from heat inside
A power supply's output rating is not its own heat dissipation. In a fictional operating case, a supply delivers 24 V at 7.5 A, or 180 W, with an assumed efficiency of 90 percent at that point. Its input power is 180 / 0.90 = 200 W; its own loss is 200 − 180 = 20 W.
Now specify where the output power goes. Of the 180 W delivered, suppose 30 W is dissipated by equipment inside the enclosure and 150 W is delivered to loads outside it. Add a separate internal device dissipating 5 W from another supply path. The total heat generated inside this model is 20 + 30 + 5 = 55 W.
The whole energy check is consistent: 205 W enters the defined system boundary and 150 W leaves electrically for the external loads, leaving 55 W as internal heat. Counting all 180 W as enclosure heat as well as the internal 30 W would double-count part of the energy and include power dissipated elsewhere.
| Item in the declared model | Power relevant to enclosure heat |
|---|---|
| PSU conversion loss | 20 W |
| Internally located DC loads | 30 W |
| Other internal device | 5 W |
| Loads outside the enclosure | Excluded from this enclosure's internal loss total |
| Total internal dissipation | 55 W |
Use actual efficiency or loss data at the relevant load, input voltage and ambient conditions for a real design. Include every significant internal heat source and identify duty assumptions. The worksheet's efficiency is not a datasheet value for an unnamed product.
Surface area and temperature rise: make the assumptions visible
For the fictional 0.6 × 0.8 × 0.25 m rectangular box, its six-face geometric area is:
A = 2 × (width × height + width × depth + height × depth)
A = 2 × (0.6 × 0.8 + 0.6 × 0.25 + 0.8 × 0.25)
A = 1.66 square metres
That area is not automatically the effective heat-dissipating area. A wall-mounted rear face, adjacent enclosures, mounting conditions and different exposed surfaces affect the thermal assessment. Simply replacing an unknown effective area with the largest geometric total can give a misleading result.
Rittal's climate-control calculation reference expresses heat transfer using effective surface area, a heat-transfer coefficient and a temperature difference. For a simplified sensitivity exercise, use temperature rise = heat loss / (coefficient × effective area). This is a steady-state lumped model, not a detailed prediction of a CPU's local air temperature.
Assume, solely for the worksheet, an effective area of 1.2 m² and a coefficient of 5 W/m²/K. With 55 W internal loss, the calculated rise is 55 / (5 × 1.2) = 9.17 K, rounded to two decimal places. With an outside ambient of 35 °C, the model's internal temperature is 44.17 °C.
| Heat loss | Effective area | Coefficient | Outside ambient | Calculated internal temperature |
|---|---|---|---|---|
| 55 W | 1.2 m² | 5 W/m²/K | 35 °C | 44.17 °C |
| 55 W | 1.2 m² | 5 W/m²/K | 45 °C | 54.17 °C |
| 110 W | 1.2 m² | 5 W/m²/K | 35 °C | 53.33 °C |
| 55 W | 0.8 m² | 5 W/m²/K | 35 °C | 48.75 °C |
| 55 W | 1.2 m² | 3 W/m²/K | 35 °C | 50.28 °C |
These rows show sensitivity to assumptions. They do not identify the correct coefficient or effective area for stainless steel, painted steel or a particular enclosure. They also omit solar gain, transient behaviour and local hot spots. Compare an appropriate manufacturer calculation and the required verification evidence before using a thermal result for equipment selection.
There is no universal rule that every IP65 panel above 40 or 50 W requires a heat exchanger. The decision depends on the enclosure, environment, losses and permissible temperatures. A wattage threshold without those conditions is not a defensible design rule.
Airflow and component placement need a real path
In natural convection, warmer air tends to rise. A heat-producing device below another device can therefore warm the air reaching it; placing the hotter component below the cooler one does not inherently protect the cooler device. Forced airflow introduces its own inlet, outlet and recirculation paths.
Mark the intended air paths and check for blocked vents, wiring ducts across openings, short-circuiting airflow and hot discharge directed at sensitive equipment. Follow each device's permitted orientation. Avoid replacing this review with a universal “power at the top” or “power at the bottom” instruction.
An internal circulation fan and a system that exchanges heat with the surroundings solve different problems. Moving air inside an enclosure may reduce temperature differences, but the heat still needs an appropriate route out. Cooling selection should also account for environmental protection, maintenance and the actual temperature relationship between inside and outside.
IP rating, corrosion and condensation are different questions
IEC 60529 classifies degrees of protection provided by enclosures through the IP code. The first digit addresses access to hazardous parts and solid-object ingress; the second addresses harmful water ingress under specified tests. It is not a general declaration of corrosion life, airtightness or suitability for every cleaning process.
Do not treat a higher final digit as covering every lower water-exposure category. Schneider Electric's IP protection explanation specifically distinguishes IP67 immersion protection from IP66 jet protection. Check the ratings actually declared for the intended exposure rather than substituting one test for another.
For a coastal location, consider the actual corrosive atmosphere, materials, finish and maintenance requirements. For a washdown area, establish the cleaning conditions and compatibility of the complete arrangement. “Durban” or “Cape Town” alone is not enough information to choose the enclosure and accessories.
Rittal's enclosure application guidance discusses corrosion, outdoor exposure, sunlight and condensation separately from a basic IP designation. A well-sealed enclosure can still experience internal condensation as temperatures change. The IP code does not establish that moisture can never form inside.
Door devices, gland plates, cable entries, unused openings and ventilation accessories are part of the completed arrangement. Follow the enclosure and accessory instructions and retain the relevant evidence. A rating printed on the original empty box does not justify arbitrary cutouts or unverified modifications.
Segregation, cable bends and access belong on the drawing
Classify the circuits and routes before allocating ducts. Identify supply conductors, switched power, drive-related cables, communications and sensitive measurement signals. Use the matching equipment and cable guidance for separation, crossings, shielding and bonding. There is no single distance that establishes acceptable EMC performance for every circuit pair.
Likewise, a signal being 4–20 mA does not justify reducing separation by an invented fixed immunity factor. Nor should a generic tutorial prescribe one shield connection arrangement for every installation. Record the applicable requirement and show how the route satisfies it.
Cable bend requirements must come from the selected cable and connector information, including whether the requirement concerns fixed or moving use and how the radius is defined. A gland-to-terminal distance is not automatically a bend radius. Review the actual three-dimensional route, connector exit direction and available depth.
Include the door sweep, hinge-side cable movement, plug withdrawal and access to terminals. Consider how a maintainer will identify a component and replace it without disturbing unrelated connections. These observations can expose a problem that a flat arrangement of component rectangles misses.
Build a useful learning portfolio and review package
For this guide's exercise, submit the declared backplate zones, both clearance-envelope arrangements, the terminal schedule and the heat-loss calculation. Keep the failed side-by-side arrangement: explaining its 30 mm shortfall demonstrates why reserved space matters. Record the assumptions beside the results so another learner can repeat them.
Use the PLC wiring lesson catalogue to select the available wiring and fault-finding exercises. The reviewed catalogue distinguishes lesson scope and access tiers. It is not evidence of a native panel CAD tool, thermal solver or corrosion-life predictor.
For the connection-learning part, review the Wiring Tutor learning tools. Keep virtual circuit work separate from enclosure engineering and physical installation assessment. A correct simulated connection does not verify clearances, temperature rise or the protection of a constructed assembly.
Link observations back to fault-finding workflows when a review raises an unresolved question. State what evidence would resolve it, instead of replacing an unknown with a confident assumption.
Questions South African learners should ask about panel training
Can I learn control-panel layout online?
You can practise reading drawings, calculating occupied space, building component schedules and reviewing declared thermal assumptions online. Physical construction and verification need suitable equipment, supervision and applicable procedures. Ask a provider which outcomes are assessed through documents, virtual exercises and practical work.
What should a Johannesburg or Durban panel-wiring course include?
Request a sample project and assessment criteria. Look for exact component documents, usable-space calculations, clear circuit identification, service access and an explanation of the limits of each calculation. Compare the electrician learning route with the wider course offer rather than choosing solely from a city keyword or an attractive cabinet photograph.
Is this worksheet enough to approve a real control panel?
No. It checks declared geometry and energy arithmetic. A real assembly requires the relevant design, installation and verification work for its equipment and application. Keep the learning result precise: it demonstrates how to organise and question evidence, while leaving product-specific and assembly-level requirements to the appropriate engineering process.