12.2.1 A main source of electrical power of sufficient
capacity to supply all those services mentioned in 12.1.1 shall be provided. The main source
of electrical power shall consist of at least two generating sets.
12.2.2 The capacity of these generating sets shall
be such that, in the event of any one generating set being stopped
or failing, it will still be possible to supply those services necessary
to provide the normal operational conditions of propulsion and safety.
Minimum comfortable conditions of habitability shall also be ensured
which include at least adequate services for cooking, heating, domestic
refrigeration, mechanical ventilation, and sanitary and fresh water.
12.2.3 The arrangements of the craft's main source
of electrical power shall be such that the services referred to in 12.1.1.1 can be maintained regardless
of the speed and direction of the propulsion machinery or shafting.
12.2.4 In addition, the generating sets shall
be such as to ensure that, with any one generator or its primary source
of power out of operation, the remaining generating set shall be capable
of providing the electrical services necessary to start the main propulsion
plant from dead craft condition. The emergency source of electrical
power may be used for the purpose of starting from a dead craft condition
if its capability either alone or combined with that of any other
source of electrical power is sufficient to provide at the same time
those services required to be provided by 12.7.3.1
to 12.7.3.3 or 12.7.4.1 to 12.7.4.4 or 12.8.2.2.1 to 12.8.2.2.4, as appropriate.
12.2.5 Where transformers constitute an essential
part of the electrical supply system required by this section, the
system shall be so arranged as to ensure the same continuity of supply
as is stated in 12.2.
12.2.6 A main electric lighting system which shall
provide illumination throughout those parts of the craft normally
accessible to and used by passengers and crew shall be supplied from
the main source of electrical power.
12.2.7 The arrangement of the main electric lighting
system shall be such that a fire or other casualty in spaces containing
the emergency source of electrical power, associated transforming
equipment, if any, the emergency switchboard and the emergency lighting
switchboard will not render inoperative the main electric lighting
systems required by 12.2.6.
12.2.8 The main switchboard shall be so placed
relative to one main generating station that, as far as practicable,
the integrity of the normal electrical supply may be affected only
by a fire or other casualty in one space. An environmental enclosure
for the main switchboard, such as may be provided by the machinery
control room situated within the main boundaries of the space, shall
not be considered as separating the switchboards from the generators.
12.2.9 The main busbars shall be subdivided into
at least two parts which shall be connected by a circuit-breaker or
other approved means. So far as is practicable, the connection of
generating sets and any other duplicated equipment shall be equally
divided between the parts. For category B craft, each part of the
main busbars with its associated generators shall be arranged in separate
compartments.