Equipment numbers are generic part numbers that are assigned to devices in a project in the preliminary design stage. There is a part database record for each equipment number that includes any necessary data such as description, voltage or current values, etc. Equipment numbers can be exchanged for real part numbers later when it is time to assign a specific vendor part, however users retain the option to display either equipment numbers or part number in the drawing.

Equipment numbers would be used, for example by a large engineering firm (EPC) who would create single line drawings with equipment numbers assigned to each device. The EPC needs to define equipment ratings and sizes but is not concerned with specific manufacturers. The EPC would then turn the project over to a control system integrator to complete the design. The system integrator would complete the design, assign the desired part numbers and return the project to the EPC.

Equipment numbers are also useful for companies that supply end user documents with company-specified reorder numbers instead of true manufacturer's part numbers.