How to Determine Electrical Enclosure Dimensions
Learn how to determine electrical control cabinet dimensions based on component layout, usable mounting plate dimensions, wiring clearance, and heat dissipation, with a practical sizing example.
How to Determine Electrical Enclosure Dimensions
When selecting an electrical enclosure, it is not enough to check whether circuit breakers, PLCs, contactors, and other components will physically fit inside. Wiring ducts, terminal blocks, cable entry points, heat dissipation, and maintenance access also affect the required dimensions.
A reliable approach is to plan the internal layout first, verify the usable mounting space, and then select the enclosure's external dimensions.
Step 1: Prepare a Component List
Start with the bill of materials (BOM) and manufacturer dimension drawings. Record each component's width, height, depth, mounting method, and wiring orientation. Also confirm:
- Which components will be mounted on DIN rails or a mounting plate, and which will be installed on the door.
- Whether cables will enter from the top or bottom, and where terminal blocks and wiring ducts will be positioned.
- Whether the equipment manuals specify minimum clearances for ventilation, wiring, or maintenance.
For example, Schneider Electric notes that the enclosure dimensions for certain PLC systems depend on the number of controllers, expansion modules, and other devices, together with the required installation clearances. Clearance requirements vary by model and should not be applied universally.
Step 2: Calculate Width, Height, and Depth Separately
| Dimension | Main considerations | Sizing approach |
|---|---|---|
| Width (W) | Components in each row, side wiring ducts, installation clearances | Use the widest required row layout |
| Height (H) | Multiple component rows, horizontal wiring ducts, terminal areas, cable entry space | Add the heights of all required vertical sections |
| Depth (D) | Deepest component, mounting plate position, connectors, cable bending space, door-mounted accessories | Verify the actual usable installation depth, not just the external depth |
External enclosure dimensions are not the same as mounting plate dimensions. For example, the Rittal AX 1468000 enclosure measures 600 × 800 × 300 mm (W × H × D), while its mounting plate measures 505 × 725 mm. Component layouts should therefore be checked against the actual mounting plate dimensions rather than the enclosure's external width and height.
Step 3: Check the Dimensions with a Layout Example
Suppose a control enclosure contains two DIN rail rows. The preliminary layout is as follows (for illustration only; these values are not universal design requirements):
| Layout item | Estimated space required |
|---|---|
| Total component width in row 1 | 330 mm |
| Total component width in row 2 | 290 mm |
| Left and right wiring ducts | 50 mm each |
| Height occupied by each component row | 130 mm |
| Wiring duct area between the two rows | 60 mm |
| Top and bottom reserved space | 40 mm each |
The initial mounting plate layout requirements are:
- Width: 50 + max(330, 290) + 50 = 430 mm.
- Height: 40 + 130 + 60 + 130 + 40 = 400 mm.
Compared with the Rittal example above, a 505 × 725 mm mounting plate can accommodate this illustrative layout in terms of its two-dimensional area. However, this alone does not confirm that the enclosure is suitable. DIN rail positions, terminal blocks, mounting holes, door-mounted devices, and available installation depth must still be checked.
If the deepest component is 170 mm, additional space may be needed for the mounting structure behind it, front-facing connectors, and cable bending. A nominal enclosure depth of 300 mm does not automatically mean that 300 mm of usable installation depth is available.
Step 4: Verify Heat Dissipation and Site Conditions
Heat-generating devices such as variable frequency drives (VFDs) and power supplies can affect the internal layout. For example, Schneider Electric specifies clearances of at least 100 mm for certain ATV630 drive configurations and mounting arrangements. This is a model-specific requirement, not a universal clearance for every device or enclosure.
For low-voltage assemblies containing significant heat-generating loads, also assess power losses, ambient temperature, and the ventilation or cooling solution. Temperature-rise verification should be carried out according to the applicable standards. IEC TR 60890:2022 provides a calculation method for determining the temperature rise of air inside certain low-voltage switchgear and controlgear assemblies.
Before finalizing the dimensions, check that the installation site provides adequate room for door opening, wiring, and maintenance. Also consider the plinth, cable entries, access routes, and any constraints on handling or moving the enclosure.
What Information Should You Provide Before Requesting a Quote?
When contacting an enclosure supplier, provide the BOM, dimensions of major components, preliminary layout drawing, mounting method, cable entry direction, required IP rating, and installation environment.
This information helps the supplier determine whether a standard enclosure will work or whether customized cutouts, a mounting plate, or structural modifications are required.
Conclusion: Sizing an electrical enclosure is not simply a matter of adding extra space around components. Determine the required mounting plate area from the actual layout, verify usable depth based on equipment and wiring requirements, and then select the external dimensions based on thermal management, maintenance access, and site conditions.
References
- Rittal AX 1468000: External and mounting plate dimensions
- Schneider Electric: Enclosing the TM5 System
- Schneider Electric: ATV630 installation clearances (example model)
- IEC 62208:2023: Empty enclosures for low-voltage switchgear and controlgear assemblies — General requirements
- IEC 61439-1:2020: Low-voltage switchgear and controlgear assemblies — General rules
- IEC TR 60890:2022: A method of temperature-rise verification of low-voltage switchgear and controlgear assemblies by calculation