Motion picture projection; an elementary text-book (1921)

Record Details:

Title:
Motion picture projection; an elementary text-book
Date:
1921
Publisher:
New York, Theatre Supply Co.
Volume:
Motion picture projection; an elementary text-book
Leaf #:
00086
Language:
English
Collection:
Books
Format:
Books
Contributor:
University of California Libraries
Sponsor:
MSN
Coordinator:
Media History Digital Library
Description:
Date Added:
July 19, 2022
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MOTION PICTURE PROJECTION 85 TESTING FOR GROUNDS Always remember that like poles repel each other while unlike poles attract each other, in other words the negative polarity is attracted by the positive polarity, and vice versa, while the negative has no attraction for negative nor the positive for positive. The positive wire of one system will have no attraction for the negative wire of any other system 4 except its own, nor will the negative of one system find any attraction in the positive of any other system. A ground is merely the current from one polarity being attracted by the opposite polarity, through the ground or some conducting medium other than that in the circuit. Supposing that we are working on a three wire system and our neutral wire is grounded, and that we take and connect one of the outside wires to the upper jaw of arc lamp, and we connect the neutral wire to the lower jaw (the neutral wire now acts as negative to the -upper or positive wire). We now ground the machine by connecting the metal framework of machine to the conduit coming in booth. Our machine now becomes grounded on the neutral because we have made contact between the frame of machine and the already grounded conduit. Should we now connect our test lamp between the upper jaw of arc lamp and frame of machine or lamp house we will naturally get a light as we are connected between the two polarities of the system.