The manufacture of most equipment includes various levels of quality control including inspections, verifications, and other quality control processes as part of their overall quality assurance programs. Most large infrastructure equipment such as chillers, generators, and UPS systems are subjected to some manner of operational testing prior to shipment. Even so, it is not uncommon for manufacturing defects, assembly errors, and other discrepancies to slip through. Specifying more stringent and project specific inspections, certifications, and testing is referred to as factory acceptance testing. When the owner also requires these tests and inspections be witnessed by their project team this becomes known as factory witness testing (FWT).
There are many benefits to requiring FWTs, but like pretty much everything else, there are associated costs. The overarching justification for doing FWTs is that any issues or discrepancies identified at the factory can be much more easily resolved prior to shipment than after the equipment arrives on-site. The decision to include FWTs in the purchase of equipment should be based on what value-add the FWT provides, the risks of not doing FWTs, and the costs (in both time and money) of performing the FWTs. In general, requiring FWTs for simple, mass-produced and standardized products with short or no lead times would be overkill. On the other hand, complex, customized, and long lead time equipment can be good candidates for FWTs. An excellent example would be switchgear. If the switchgear is standard without any complex controls, then maybe FWTs would not add much value. If the switchgear is for paralleling multiple generators and includes closed-transition between utility and generator sources with an integral PLC controller and site-specific sequences-of-operations, then requiring FWTs are certainly appropriate.