Figure 6-5, view A, shows the main motor control- ler wiring diagram for the steering system shown in figure 6-3. This wiring diagram can be used to trou- bleshoot, check for proper electrical connections, or completely rewire the controller. SCHEMATIC DIAGRAM.—The  electrical  sche- matic diagram describes the electrical operation of a particular piece of equipment, circuit, or system. It is not drawn to scale and usually does not show the relative positions of the various components. Graphic symbols from ANSI Y32.2 represent all components. Parts and connections are omitted for simplicity if they are not essential to show how the circuit operates. Figure 6-5, view B, shows the schematic diagram for the steering system main motor controller that has the following electrical   operation: Assume 450-volt, 3-phase power is available on lines 1L1, 1L2, and 1L3; and 2L1, 2L2 and 2L3; and the receiver selector is set so that the motors are to idle as  standby  equipment.  Then  turn  the  master  switch (MM and SPM push-button station) to the start position to energize coil 3M. Coil 3M will close main line contacts  3M,  starting  the  servo  pump  motor.  When contacts 3M close, auxiliary contacts 3Ma and 3Mb also close. Contacts 3Ma shunt (bypass) the master switch start contacts to maintain power to coil 3M after the master switch is released. When released, the master switch spring returns to the run position, closing the run contacts and opening the start contacts. Turning the switch to the stop position opens the run contacts. Contacts 3Mb energize latching coil CH, closing con- tacts  CH,  and  energizing  coil  1M,  which  closes main line contacts 1M to start the main pump motor. (Solenoid  latch  CH  prevents  contacts  1M  from  opening or closing due to high-impact shock.) Before the motors can deliver steering power, the receiver selector switch must be set to the appropriate receiver, closing contacts RSSa and RSSb. Contacts RSSa energize coil 2M, which closes contacts 2M to supply  single-phase  power  to  the  synchro  system.  Con- tacts RSSb shunt the start and 3Ma contacts so that in case of a power failure the motors will restart automat- ically upon restoration of power. In case of overload on the main or servo pump motor  (excessive  current  through  IOL  or  3OL), overload  contacts  1OL  or  3OL  will  open, de-energizing coil 3M to open line contacts 3M and stop the servo pump motor. When line contacts 3M open, contacts 3Ma and 3Mb open, deenergizing Figure 6-4.—Ship's service generator and switchboard interconnections, single-line diagram. 6-7