Before placing any PLC modules on the mixed rack, technicians must confirm that the mounting surface is flat within the allowed tolerance, with no uneven spots that could create mechanical stress on the rack base after tightening. The combined layout drawing should mark out which sections of the rack are arranged horizontally and which are oriented vertically, to ensure the final installation matches the pre-planned thermal dissipation and wiring routing logic. All mounting holes on the panel or DIN rail base should be deburred and cleaned of leftover metal shavings, so the rack can sit completely flush against the supporting surface without wobbling.

Horizontal section layout and load distribution
On the horizontally mounted part of the rack, arrange heavy components such as power supply units and high-density backplane bases at the lower horizontal positions, to keep the overall center of gravity low and reduce long-term mechanical deformation under vibration. Leave consistent empty space between adjacent module units along the horizontal plane, so natural convection air can flow freely around each module’s heat generating surface without being blocked by neighboring units. Every module on the horizontal section should be pushed firmly against the DIN rail until the locking clip clicks into place, and a gentle side pull test should be performed to confirm no unit can shift loose under normal operational vibration.

Vertical section alignment and stress control
For the vertically oriented segments of the mixed rack, make sure the long axis of each PLC module runs parallel to the vertical mounting surface, so heat generated from internal components can rise naturally along the module’s metal heat sink instead of being trapped against the rack wall. Avoid placing modules with high processing load and high heat output at the very top of the vertical segment, as accumulated hot air from lower units will raise the ambient temperature around these modules beyond their rated operating range. The mounting screws for the vertical rack section should be tightened in a diagonal sequence, to distribute clamping force evenly across the entire vertical base and prevent twisting that would misalign the backplane connector slots.

Transition area wiring and stability verification
At the intersection between horizontal and vertical rack segments, reserve dedicated wiring channels that separate power cables from signal communication lines, to prevent electromagnetic interference from affecting high-speed data transmission between modules across the two orientations. The backplane bus that connects horizontal and vertical sections must be secured with locking clips at both ends, so relative movement between the two rack parts will not pull the bus connector loose over time. After all modules are mounted, perform a full swing and shake test on the entire rack assembly, and check every module’s indicator light status to confirm no internal connection has been disrupted during the installation process.