(b) From the casemate generator: Both circuit breakers are closed and switch No. 2 is closed to the left (facing the board).
The operating board.—A front view of this is given in [figure 3], its wiring diagram in figure 18 at the end of the book. One is required for each group of 19 mines. It consists of an iron frame to which are attached a signal block, a master block, 19 mine blocks (1 for each mine), busses, and a terminal bar with 19 numbered terminals. The frame is 78 inches high by 24 inches wide. It should be set up so that its face is 34 inches from the wall in rear.
The signal block (see fig. 18).—This is an enameled slate block 24 inches wide and 11 inches high, upon which are mounted three binding posts, three lamps (red, white, and green), a bell and bell switch, a 90-ohm non-inductive resistance in parallel with the white lamp, and a 125-ohm resistance in series with the bell. The binding posts are marked “Earth” or “G.,” “A. C.,” and “D. C.,” respectively. The bell, the 90-ohm non-inductive resistance, and the 125-ohm resistance are so indicated on the figure. The lamps are marked as follows: Red, “R. L.”; white, “W. L.”; green, “G. L.”
The circuit, under normal conditions, is: From negative D. C. bus on power panel, to switch 3 closed up, to “operating board” terminal, to D. C. lead, to D. C. post on signal block, through green lamp, to D. C. jaw on master block, to D. C. bus on operating board, through power switch P on mine block, through solenoid S, to middle of testing switch T, to upper contact of same, to upper contact of automatic switch A, to middle of same, to mine switch M, through same to terminal bar, through 19-conductor and single-conductor cables, through mine transformer primary, to mine case, to ground, to D. C. “earth” terminal on power panel, to switch 3, and to positive D. C. bus on power panel.
Green lamps of 8, 16, and 32 candlepower are supplied. The 16-candlepower green lamp glows dimly when 19 mines are connected to the operating board and all are free from short circuits, grounds, or abnormal resistances. If it should glow abnormally bright, due to grounds, a 32-candlepower lamp should be substituted. If it should glow very dimly, due to a less number of mines connected, an 8-candlepower lamp should be used.
A short circuit in a mine circuit causes the green lamp to glow more brightly.
Breaks in conductors not causing short circuits will not be revealed ordinarily by this lamp. To detect breaks, tests of individual mines must be made.
The red lamp glows and the bell rings when any automatic switch is down. The circuit under this condition is:
From negative D. C. bus on power panel to switch 3 closed up, to “operating board” terminal, to D. C. lead, to D. C. post on signal block, through green lamp to D. C. jaw, to D. C. operating board bus, through power switch on mine block whose automatic switch is down, through insulated pin of lower arm of automatic switch, to lower point of testing switch T, to operating board lamp bus, through bell, 125-ohm resistance and bell switch, and red lamp in parallel, to “earth” post, to earth lead, to D. C. “earth” terminal on power panel, to switch 3, and to positive D. C. bus on power panel.
The resistance of the bell is such that a resistance of 125 ohms must be placed in series with it to make the joint resistance of the red lamp-bell circuit so large that if one automatic switch is down it will not interfere with the tripping of another.