this ring circuit usually has a normally open point, the purpose of
which is to minimise the number of customers affected by the faulted
section of the ring circuit
• ring main switches are manually operated; hence fault location and
customer reenergisation is time consuming; a modern tendency
is for the ring main switches to be fitted with remotely operable
mechanisms such that switching times can be reduced by allowing
remote substation facilities or, with modern intelligence systems,
to allow automatic deenergisation and isolation of a faulted section
and reenergisation up to the point of the fault
• the tee-off point of the ring circuit feeds via an 11 kV/415V, threephase
transformer to an LV fuse board, typically having up to five
outgoing circuits which feed directly to large customers or groups
of customers; in most of these LV circuits, it is possible to achieve
an LV backfeed from an adjacent ring main unit, thus maximising
the number of customers on supply while fault repairs are in
progress