Enclosure bill of materials: structure it for assembly

Put the enclosure in the finished-assembly bill of materials, alongside the PCB assembly, mounting hardware and cable-entry components. Keep the PCB assembly BOM distinct when that board is built, stocked or serviced separately. A flat purchasing list can still work for a simple build, provided its quantities and revisions come from controlled records. The important distinction is between what you assemble and what you buy, not which software exports the list.

What you need before building the list

Start with the physical assembly and its purchasing boundaries. Decide whether you buy a completed PCB assembly or build it from individual components. Then identify which mechanical parts arrive with the enclosure and which require separate ordering.

Gather these records before creating the released BOM:

• The finished-assembly drawing, showing how the enclosure, board and hardware fit together.
• The PCB assembly identifier, revision and its separate component BOM, where applicable.
• The enclosure drawing, including material, dimensions, openings and mounting details.
• Cable outside diameters and the selected cable-entry component specifications.
• Hardware descriptions covering dimensions, materials, quantities and installation requirements.
• A defined build quantity and a consistent unit of measure for every purchased item.

Distinguish a bare enclosure from a purchased enclosure package. If mounting hardware is included, document that inclusion rather than ordering it twice. If inclusion is uncertain, resolve it before release.

For factory openings, use the custom stainless enclosure and cutout drawing checklist. The BOM identifies the required item; the drawing defines geometry that a short purchasing description cannot capture.

Build the finished-assembly BOM

1. Define the finished assembly as the parent.

   Give the completed unit a controlled assembly identifier and revision. Its BOM should identify everything installed during final assembly, including the enclosure and the completed PCB assembly.

   The enclosure and PCBA normally appear at the same level when neither is supplied as part of the other. The PCBA then has its own child BOM for components installed during board assembly. Assign items by the actual manufacturing boundary, not simply by whether they are electrical or mechanical.

2. Choose a structured BOM or a controlled flat list.

   A flat list can be sufficient when one build uses one board and you manage all purchasing together. Include an assembly-stage field so board components remain distinguishable from enclosure hardware.

   Use a parent assembly with separate child records when boards are reused, stocked, subcontracted or supplied as spares. That structure lets the same PCBA revision appear in several finished products without copying its component list.

   A structured assembly BOM and a flat purchasing export can coexist. The export should be generated from the released structure, rather than maintained as a competing master list.

3. Create a controlled enclosure item.

   Identify the exact enclosure configuration, not just a general description such as “stainless box.” Record the material, dimensions, drawing reference and revision needed to distinguish it from similar configurations.

   State the dimension order explicitly, such as width × height × depth. Identify whether dimensions describe the enclosure body, usable internal space or another drawing feature. Never assume external dimensions prove component fit.

   If you need a new body size or opening layout, custom enclosures let you define material, width, height, depth and every cutout. Keep those requirements tied to the enclosure item and its approved drawing.

4. List installation hardware and cable-entry parts.

   Count standoffs, screws, nuts, washers, cable glands and unused-entry plugs from the assembly drawing. Specify enough detail to prevent substitution with a physically similar but unsuitable item.

   A gland entry needs the selected component identifier and the cable diameter it must seal. Its mounting interface must match the enclosure opening. Cable support may also require a separate clamp or restraint; the cable strain relief article explains that distinction.

   For board mounting, specify the complete attachment arrangement. The PCB mounting article covers approaches when the enclosure has no existing posts. Do not leave standoff height or fastener engagement to purchasing assumptions.

5. Set quantities and units at each assembly level.

   Each child quantity should state the amount required for one parent assembly. Multiply by the production quantity only when preparing purchasing or work-order requirements.

   The following excerpt illustrates the structure, not a complete assembly or a supplied enclosure configuration. Its quantities apply only to this hypothetical design.

   Assembly level	Item	Quantity per immediate parent	Unit	Controlled reference
   Parent	Finished enclosed assembly	1	each	Finished-assembly drawing and revision
   Child	Configured enclosure	1	each	Approved enclosure drawing and revision
   Child	Completed PCB assembly	1	each	PCBA identifier and revision
   Child	PCB support standoff	4	each	Selected hardware specification
   Child	PCB retaining screw	4	each	Selected hardware specification
   Child	Cable gland	2	each	Selected gland specification

   For ten assemblies using this example, the net requirement before stock adjustments is twenty cable glands. Purchasing pack quantities belong in purchasing data; they should not change the assembly requirement of two glands per unit.

   Keep manufacturing spares and procurement allowances separate from installed quantities. Otherwise, future exports can multiply an allowance as though every assembly consumes it.

6. Connect every custom item to a released drawing.

   Record the drawing number and revision in controlled fields or through an unambiguous linked item record. Do not rely on a filename containing “latest.”

   The drawing should control opening sizes, positions, tolerances, mounting orientation and sealing interfaces. Use the cutouts, glands and HMI windows guide for those fundamentals rather than crowding them into the BOM description.

   Record the required enclosure rating and the configuration supporting it. Our enclosure ratings are manufacturer ratings for the specified design; the enclosures are not UL listed. Adding a rating to a BOM description does not establish that rating for the finished assembly.

   The NEMA enclosure drawing callout article explains how the drawing should communicate the required protection and construction details.

7. Release the assembly package and generate purchasing requirements.

   Release the parent BOM, relevant child BOMs and drawings as a coordinated package. Capture the applicable revisions so a later change does not silently alter an existing build.

   If you purchase a completed PCBA, buy that assembly rather than also purchasing its entire component list. If you assemble it internally, generate component requirements through its child BOM. Apply the same rule to enclosure packages containing purchased accessories.

   When design software cannot represent the mechanical items cleanly, maintain a controlled parent BOM outside it. Do not add misleading electrical connections or board footprints merely to force an enclosure into an export. Use documented mechanical-item or BOM-management features where available.

Check the released package

Check the BOM against the assembly drawing and the actual purchasing arrangement. A correct component count does not prove that the parts fit together.

• Confirm that the purchased enclosure matches the approved drawing revision.
• Check board position, standoff height, connector access and cable bend space.
• Verify that screw lengths suit the complete material stack without contacting circuitry.
• Match each cable gland to its cable diameter, opening and installation requirements.
• Confirm whether gaskets, mounting parts and entry accessories are included or separately purchased.
• Verify that unused openings have specified closures where required.
• Check that purchased subassemblies and their individual components are not both counted for procurement.
• Confirm that approved substitutions preserve fit, sealing, material compatibility and required approvals.

Perform a quantity check using a representative production quantity. Then compare the generated purchasing list against the released parent and child records. Every required item should have a traceable source, including manually added mechanical parts.

Mistakes that break purchasing or the rating

Treating the BOM as a substitute for the drawing. A description cannot reliably communicate opening locations, tolerances and rear clearances. Keep geometric requirements on the controlled drawing.

Using a generic enclosure description after modifying it. A body with new openings is a distinct configuration. Review the modified design and its rating requirements rather than inheriting the unmodified description.

Allowing unrestricted gland substitutions. Matching the mounting opening alone is insufficient. Cable sealing range, panel thickness, gasket arrangement and environmental suitability also matter.

Counting complete assemblies and their contents twice. A flattened purchasing report must respect whether each subassembly is bought complete or manufactured internally.

Editing only the exported spreadsheet. That correction disappears on the next export unless it is incorporated into the controlled source. If the spreadsheet is the master, give it a revision and release process.

Assuming every mechanical item belongs outside the PCBA BOM. Some board assemblies include fitted heatsinks or other mechanical parts. Define ownership by assembly stage and supply scope, then apply that rule consistently.

What to send with the enclosure order

Send the enclosure item identifier, required quantity and approved drawing revision. Include material, width, height, depth, opening details, mounting requirements and the required enclosure rating.

Identify which accessories you expect within the enclosure supply scope and which you will install separately. Provide component drawings where gland, display or mounting interfaces depend on their geometry.

For custom work, fabrication starts from your approval of the drawing we send back. Before approval, reconcile that drawing against the enclosure BOM entry and the finished-assembly drawing. Release any resulting revisions together. This keeps the ordered enclosure, the assembly instructions and the purchasing record aligned.

Enclosures for this job

Catalog sizes that suit the job this article answers, picked from its subject; open one for its full specifications.

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