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94 HANDBOOK OF PROJECTION FOR
In Fig. 13, A is a D. P. S. T. and B a T. P. S. T. knife switch, without fuse contacts; C is a D. P. S. T. knife switch with knife blade cartridge fuses, and D a D. P. S. T. knife switch with ferrule contact cartridge fuses. For explanation of the different kinds of fuse contacts see "Fuses," page 107.
In Fig. 13, E and F are types of porcelain base D. P. S. T. switches, with receptacles for plug fuses. This type of switch is called a "panel cutout." It is often used in building up panel boards, but may only be used to control individual circuits of low amperage.
ENCLOSED SWITCHES.— An enclosed switch is one having an individual protecting cover, usually of sheet metal which entirely encloses and protects all "live" parts of the switch. All projector switches are and must be enclosed switches, no other kind being permitted for this purpose. The enclosure of the switch by a metal covering is to protect the projectionist from possible shock by accidental contact with its live parts, as well as to prevent possible short circuits or injury to the switch by contact with various objects. It is important that the covering of enclosed switches be so made that it cannot come into contact with the live parts of the switch.
In connecting enclosed switches it is better that the blade end 'of the switch be dead when the switch is open. In fact that rule applies to all switches, though sometimes circumstances prevent its being adhered to.
LOCATION OF SWITCHES.— In the location of switches local conditions must, of course, largely govern, particularly in the smaller theatres, but the house switchboard should be so located that the man in charge of it will have an unobstructed view of the screen when at the switchboard. Unless this be done there is apt to be an imperfect handling of the house lighting at the beginning and the end of the show, or at other points where change in the auditorium lighting may be necessary, no matter what care may be taken to co-ordinate the work of the projectionist and the work of the switchboard man.
Switches governing emergency lights, which include all lights kept burning during the performance, should under no circumstances be placed on the main switchboard. You can never tell what an excited man will do, and in case of fire people inside the auditorium, including the employees, are apt to become excited. Some one might pull the emergency light