Planning a 19-inch rack: U, mounting depth and room for cables

What 19 inches and rack units actually describe

19 inches describes the front mounting format, not the freely usable interior of a case. Equipment height is stated in rack units, abbreviated U or RU internationally; the German abbreviation is HE. One U equals 44.45 millimetres. Actual front-panel height allows for construction clearances and is therefore not simply the available interior height.

For an initial list, a table with every device name and its specified U count is enough. Add items such as drawers, connector panels and shelves. An empty area can be deliberately planned, for example for a later addition. Ventilation clearances, however, can only be established from the respective equipment documentation.

Maximum depth extends beyond the enclosure

For each device, record the depth from the intended mounting plane. Then consider it connected: plugs, strain relief and the necessary cable routing need additional space. Also check controls and handles protruding at the front. A rack case's external depth alone does not reveal the space available between rails, lids and installed parts.

A useful planning view shows the deepest device from the side with cables connected. Mark the front mounting rail and areas that must remain clear. If a lid is fitted for transport, include its interior in the drawing. Cables should neither be pinched by the lid nor pressed against connectors by excessively tight routing.

Check weight and heat separately

A suitable front width says nothing about how a heavy device must be supported. Check the installation instructions for rear support, rails or other required fixings. Document the weight of each installation and consider the rack as a complete unit: devices, enclosure, shelves, cables and accessories all contribute to the total load.

For operation, airflow needs planning as specifically as the signal path. Where does a device take air in and release it? An enclosed compartment or adjacent drawer may be poorly positioned for some devices. For rack drawers, Penn Elcom expressly refers to the ventilation requirements of nearby heat-producing devices. An arbitrary ventilation panel alone does not demonstrate sufficient cooling.

From diagram to assembled rack

Mentally walk through the later setup. Which connections remain permanently plugged in and which are made on site? Must rear panels be reached regularly? Where are the accessories needed to start? Label the planned positions in the drawing so that a substitute operator can also identify the system.

A simple example is mobile audio equipment with receivers and an accessory drawer. Adding their U values only gives the initial space allocation. Weight, antenna connections, airflow and rear access are checked afterwards. This example describes a planning method, not a specific DM-Cases reference.

• Record model, U, mounting depth and weight for each device.
• Sketch the transport configuration with plugs and cables.
• Add installation and ventilation requirements from the equipment manuals.
• Agree access, labelling and accessory space before manufacture.

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