NHS England HTM 06-01 Electrical Services Supply and Distribution (2017 Edition) 4.2-4.3: Design to minimise single points of failure, including failures of the internal network

The design process should confirm that single points of failure that would lose supply are minimised by giving the right resilience at the point of use, and should consider every potential point of failure, including failure of the internal primary electrical infrastructure itself and not only loss of the DNO supply, transformer or main switchboard; the secondary supply design may differ for each failure type.