structure. Figures 22, 23 and 24 show various views of the operating levers on the front of the switchboard. Figure 28 shows the front of the main switchboard with all instruments and levers. All the levers used in the operation of the engines are shown in these views. The switchboard is located in the after end of the center engine room, and the operator faces aft when handling the switches. By referring to Figure 27 the relation of all the switches and levers used in the various operations can be seen. There is a disconnecting switch (already described under generators) for each main generator. These are operated in the center engine room and are mounted on the outboard bulkheads on each side. These switches are of the knife-blade type; they are mounted on large brass plates which are bolted to the bulkhead and form a part of it. Single conductor cable is used to connect the generator to the main switchboard, and it is therefore necessary to replace the part of the bulkhead surrounding the cable with non-magnetic ma terial to prevent its overheating and causing losses in the circuits. The insulators for this switch are heavy molded blocks of bakelite, which is very tough and is not susceptible to breakage by shock or vibration. The bus tie switch is mounted inside the cell structure and is operated at that point. It is also of the knife-blade type. The bus tie switch connects the starboard and port buses so that either generator can run all four motors when desired. The bus tie switch and the two generator disconnecting switches are mechanically interlocked in such a manner that only two of them can be thrown in at any one time. This makes it impossible to connect the two generators to the sam bus and thus put them in parallel. They are also mec interlocked so that the generator disconnecting switc be thrown into the low-voltage position only when the bus tie switch is closed, and into the high-voltage position only when the bus tie switch is open; this interlocking makes it certain that the generators will always be operated in the most effi |