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FOR MANAGERS AND OPERATORS
351
Fusing Projection Circuits Where Transformer is Used. — Let it be clearly understood that the term "transformer," as here used, means the low-voltage transformer commonly termed "Economizer," "Inductor," "Compensarc," etc. Before reading this, however, I would recommend the operator to turn to Page 343, and study the electrical action of these devices.
When dealing with transformers it must be clearly understood that one ampere from a 110 volt line becomes considerably more than two amperes at the 35 volt projection arc, and that one ampere from a 220 volt line becomes approximately between five and six amperes at the 35 volt arc. Let it also be clearly understood that, for the purpose of calculating, we assume the voltage of the A. C. projection arc, and therefore the voltage of the secondary of the transformer, to be 35, although it may range anywhere between 30 and 40.
This brings about a peculiar and apparently very little understood condition as applied to fusing. Almost all transformers (remember I am speaking of economizers, etc.) are fused on their primary side only. This is bad practice.
Fig. 163 is the diagrammatic representation of a transformer-controlled projection
Note. — Error: Switch 7 should be between fuses 1-1 and transformer 3.
Figure 163.
circuit in which 1-1 are the fuses at the beginning of the primary circuit, either at the operating room distribution panel or the main house switchboard, as the case may be; 2-2 are the lines from 1-1 to the transformer; 3 is the transformer; 4-4 the lines from the transformer secondary to fuses 5, and 6-6 are the lines from secondary fuses 5 to machine table switch 7. All these may be rubber covered wire, but lines 4-4 and 6-6 must be of sufficient size to ac