The use of a UPS has become routine within electrical healthcare design and is seen as the ‘go to’ solution to meet the less than 0.5s changeover times called for in Section 710 of BS 7671 and HTM 06-01. However, although frequently provided as an electrical source of safety for a Group 2 location, this equipment is often misunderstood by the designer, installing contractor and eventually the team responsible for operations and maintenance.

This means that the UPS can be incorrectly sized not just in terms of autonomy or operational capability when dealing with multiple single-phase loads across a 3-phase inverter, there are often misunderstandings relating to how the UPS will deliver the power under normal and fault conditions in both mains supported and loss of mains scenarios.
These misunderstandings lead to incorrect application of circuit protective devices leading to inadvertent compliance failures.

This presentation intends to demonstrate the limitations of a UPS to deliver expected fault current compared to that of the mains supply. This will lead onto understanding inrush of Medical IT systems and how the UPS can deliver (or fail to deliver) sufficient current to operate the relevant devices.

Finally the presentation will identify pointers as to how to specify the correct equipment and devices to comply with BS 7671 and to understand the impact on the supplies to critical equipment and potential faults within those systems.