Optic projection : principles, installation and use of the magic lantern, projection microscope, reflecting lantern, moving picture machine (1914)

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5oo INSTALLATION OF ARC LAMPS [CH. XIII INSTALLATION OF AN ARC LAMP FOR PROJECTION § 693. In the first place it is necessary to know the maximum amperage to be used for the projection. The wiring, the fuses and the ballast (rheostat, inductor, etc.) must be adapted to this maximum current. If the installation is adequate for the highest current that may need to be used, it will of course be adequate for any smaller current. For drawing, and much of the ordinary magic lantern work, the current varies from 5 to 15 amperes, and if the installation were for such work alone, wiring and accessory apparatus which is safe for 15 amperes would suffice. If, on the other hand, the line were to be used for large halls also, and especially for opaque projection (Ch. VII), then the wiring and accessory apparatus would reed to have a maximum capacity of 50 to 60 amperes. For moving pictures, the line should safely carry a maximum of 75 amperes, or finally if kinemacolor moving pictures are to be shown in a large hall, the wiring and accessory apparatus must be adapted for an amperage of 100 to 200. The size of solid wires for different currents is given in the following table : § 694. Table of allowable carrying capacity of single copper wires of 98% conductivity.* AMERICAN INSTITUTE OF ELECTRICAL ENGINEERS No. Brown and Sharp Gauge Diameter in Millimeters Diameter in inches Circular Mils With Rubber Insulation Amperes With other Insulation Amperes No. i 7.248 .289 83,690 107 156 No. 2 6-543 •257 66,370 90 131 No. 3 5.826 .229 52,630 76 110 No. 4 5.189 .'2O4 41,740 65 92 No. 5 4.620 .182 33,ioo 54 77 No. 6 4-II5 .162 26,250 46 65 No. 8 3-264 .128 16,510 33 46 No. 10 2.588 .102 10,380 24 32 No. 12 2.053 .081 6,530 17 23 No. 14 1.627 .064 4,107 12 16 No. 1 6 1.291 .051 2^,583 life ** 8^ No. 1 8 1.024 .040 1,624 3 5 *From the 1913 National Electrical Code, § 18, pp 32-33.