What Amendment 4 to the 18th Edition Wiring Regulations BS 7671:2018+A4:2026 Means For Uninterruptible Power Supplies

Amendment 4 to the 18th Edition Wiring Regulations BS 7671:2018+A4:2026 is one of the most significant revisions made in recent years. Published jointly by the IET and BSI in April 2026, the new ‘Orange Book’ consolidates all previous amendments into a single definite document.

A dedicated chapter has been introduced to discuss stationary secondary batteries, energy storage, power of ethernet and updated requirements for functional earthing of ITC systems. For Power Control Ltd and its clients working in critical and healthcare environments, the most important changes are within Section 710, which provides even clearer requirements on supply continuity and the us of UPS systems in Group 2 locations, such as operating theatres that require medical IT systems 

The revised Section 710 requires

• Two independent electrical supplies. To ensure that power continuity is sustained even in the event of a fault on one UPS system.
• A UPS system to ensure uninterrupted power supply during any transfer of fault condition 
• Both independent supplies and a UPS to be positioned as physically close to the equipment they support to avoid a dangerous loss of power by reducing cable lengths, minimising impedance and limiting the risk of interruption to supply between the power supply source and the load
• Insulation monitoring devices for medical IT systems that use a transformer to maintain supply during a first fault and alert staff to a first fault before disconnection could occur. This is to ensure power continuity whilst enabling safe intervention

For those specifying, installing or maintaining UPS systems in hospitals, surgical suites or any Group 2 medical location, Amendment 4 is no longer optional guidance. It is now the compliance standard.

Designs must now formally demonstrate two independent supplies, an appropriately rated and positioned UPS, and a compliant medical IT system with transformer and IMD.

The updated 18th Edition Wiring Regulations have a six month transition period. From 15th October 2026, the previous regulations will be formally withdrawn, meaning that all new electrical designs and installations must strictly comply with Amendment 4.

UPS systems must

• Be able to be safely isolated during any UPS maintenance or service work
• Be able to feed back to the grid safely
• Be able compliant with enhanced protective earthing requirements 

Power Control has extensive experience of designing, supplying and maintaining UPS systems for healthcare and other critical environments. We are fully versed with the new requirements and can support businesses from specification through to commissioning and ongoing maintenance.