Reliable power for a sustainable world
What Is A UPS Factory Witness Test?

Witness testing for UPS systems takes place prior to full site installation and commissioning. It simulates real-life load conditions and aims to ensure the entire UPS and its ancillary components such as switchgear work properly and meet the agreed customer and contractual specifications. 

Also known as a Factory Acceptance Test (FAT), witness testing for uninterruptible power supplies incorporates a variety of inspections and simulations based on the customer’s specific requirements. These can include: 

  • Visual inspections 
  • Static-state tests i.e. input/output stability, harmonics, operational efficiency 
  • Dynamic tests i.e. different operating modes, overloads 
  • Failure simulations i.e. battery failure, AC mains failure 


In addition to these operational tests, a UPS witness test will also incorporate conformity checks and an audit of the original contract agreement to ensure all obligations are met.  


What Are The Benefits Of A UPS Factory Acceptance Test? 

Witness tests are most common for larger-scale UPS, especially the multi-megawatt systems typically found in modern data centres. Customer representatives, specifiers, project managers and other key personnel visit the manufacturer’s site, where their technicians and engineers oversee all tests. 

From a customer’s perspective, a FAT is the ideal opportunity to get a hands-on look at their new UPS in full operational mode prior to installation. It identifies and rectifies any fundamental issues and allows for last-minute modifications. 

Manufacturers can offer some practical training and insight, which will help boost customers’ confidence when they’re operating the UPS for real. 

It also gives both sides the chance to review maintenance procedures and discuss the spare parts required for both system start-up and its ongoing operation. 

Final FAT reports also act as a template for a Site Acceptance Test (SAT) that takes place during installation and commissioning. Replicating the FAT tests during a SAT is the most effective way to confirm the UPS hasn’t been damaged during transportation.  


This video offers a glimpse into the preparations for a UPS witness test at our purpose-built facility in Wrexham on a 30 kVA Multi Sentry UPS housed in a bespoke IP54-rated electrical enclosure.  

Factory Acceptance Tests are also undertaken at Riello UPS’s state-of-the-art Italian facilities in Legnago and Cormano. These temperature-controlled environments enable our uninterruptible power supplies to be put through their paces using real-life loads.  


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