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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.