Outside Insulation

Fzavax 102.—Staggered Joint for connecting cap wires to lead wires.

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This should cause full-scale deflection of the needle. If it does not. It indicates a break or a point of high resistance, which must be repaired.

(2) After the firing wire has been tested <and repaired, if necessary) connect the Tree ends of the firing wire to the cap wires. Again touch the exploder ends of the firing wire to the galvanometer posts. If the needle moves along the scale, it Indicates that the circuit is ready for firing if due care has been exercised to Insure against shortcircuiting the cap wires while placing the charges. If the needle does not move, there is a break in the cap-wire circuit. If the needle moves only slightly, there is a place of high resistance, such as a bad joint, in the cap-wire circuit. If the caps are placed in parallel, each cap must be tested separately. Each series in a parallel series circuit must also be tested separately.

■ 54. Placing Charces.—The officer, or noncommissioned officer, in charge of each demolition project gives definite Instructions as to the sizes of charges to be used and where and how they are to be placed. Failure to use the proper amount of explosive results in failure of the demolition project, and placing a charge incorrectly may be Just as disastrous. Don't try to save yourself work by using a smaller charge or by placing the charge in a location that is easier to get to than the location directed. II, for any reason, it Is impossible to place the charge in the location or manner directed, report this fact to the officer or noncommissioned officer in charge. The following points will be helpful in enabling you to place charges properly to attack concrete, rteel, and timber.

i a. Crater.—Figure 103 Illustrates how to prepare a borehole to blow a crater with TNT. The depth of the hole determined by the officer in charge. In place of the TNT locks, one or more ammonium nitrate cratering charges pay be used.

i b. Concrete.—Because of the difficulty of placing internal charges, concrete is normally attacked by external charges

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calculated to blast through its entire thickness. In attacking a concrete wall, or a bridge abutment or pier, the entire amount of explosive is normally concentrated at the midpoint or the structure, if the width is not more than twice the thickness. Where the width is more than twice the thickness, two or more charges are used, each charge being large enough to shatter the thickness of the wall, and the

WRAP WITH TWINE OR TAPE-'

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