BS 7671 Amendment 4: Hospital Electrical Installations

The revision of Section 710 in Amendment 4 is one of the most technically significant changes, aligning BS 7671 more closely with IEC 60364-7-710:2021. For hospital electrical designers and contractors, this means updated classification criteria, revised supplementary bonding requirements, and new guidance on medical IT systems.

Group classification has been refined. Group 0 (no applied parts), Group 1 (body-contact applied parts), and Group 2 (intracardiac procedures and life-support) remain the three categories, but Amendment 4 provides more detailed classification guidance. Specific room types are now listed with their default Group classification, reducing ambiguity. For example, recovery rooms are explicitly classified as Group 1 (previously debated), and rooms with mobile imaging equipment default to Group 1 unless intracardiac procedures are performed.

Supplementary equipotential bonding in Group 2 locations has been revised. The previous requirement to bond all extraneous-conductive-parts within the patient environment remains, but Amendment 4 introduces a maximum permissible impedance between simultaneously accessible bonded parts of 0.1 ohms (previously 0.2 ohms for some configurations). This tighter requirement reflects the IEC alignment and means that existing bonding connections in older hospitals may not meet the new standard during refurbishment.

Medical IT systems (IT-M) receive expanded coverage. The insulation monitoring device (IMD) must now alarm at a threshold no higher than 50 kohms (previously implementation-dependent). The audible and visual alarm must be located where clinical staff can respond — typically at the nurse station or within the Group 2 location itself. Amendment 4 also requires periodic testing of the IT-M system at intervals not exceeding 12 months.

Changeover times for essential circuits are clarified. Circuits supplying life-support equipment in Group 2 locations must transfer to the secondary supply (generator or UPS) within 0.5 seconds. Amendment 4 specifies that this changeover time must be verified during commissioning and documented, with the test methodology described.

Socket outlet circuits in Group 2 locations must be supplied from the medical IT system or, where TN system supply is used, must have individual RCD protection with a rated residual current not exceeding 30 mA per socket outlet circuit. Amendment 4 clarifies that multi-socket outlet strips commonly used at bedsides must each be on a separately protected circuit.

ECalPro's Protection Calculator supports Section 710 medical location protection coordination, supplementary bonding impedance verification, and changeover time compliance checks.