To test the firing wire for a short circuit, separate the firing wire conductors at both ends, and connect those at
one end to the test set binding posts. Actuate the test set. The indicator lamp should not flash. If it does, the
firing wire has a short circuit.
To test the firing wire for continuity, twist the wires together at one end, and connect those at the other end to
the M51 test set posts. Actuate the test set. The lamp should flash. If it does not flash, the firing wire has a
Twist the free ends of the firing wire together after testing.
Before being hooked into the firing circuit, each blasting cap must be tested. This can be done using either the
M51 test set or the blasting galvanometer. Be sure that you use only the special silver-chloride dry-cell batteries,
BA245/U or BA-2245/U, which produce only 0.9 volts, in the galvanometer. Other batteries may produce
enough voltage to detonate electric blasting caps. Whether you use the M51 test set or the galvanometer, use the
steps that follow to test blasting caps:
Uncoil or unfold the blasting cap lead wires. Always point the explosive end of the blasting cap away from
While uncoiling or unfolding the cap lead wires, hold the blasting cap by the wires, approximately one inch
from the cap.
Carefully extend the cap lead wires to their maximum length. Straighten them out by hand. Do not throw,
wave, or snap the blasting cap to loosen the coils or folds.
Place the blasting cap under a sandbag or a similar object to prevent injuries in the event of a premature
Remove the shunt from the blasting cap lead wires. The soldier removing the shunt from a blasting cap's lead
wires must ground himself or herself by grasping the bare ends of the firing wire or by touching the bare
ground. This prevents accumulated static electricity from detonating the blasting cap.
If using the M51 test set, attach one cap lead wire to each test set binding post and squeeze the test set handle.
The blasting cap is satisfactory if the indicator lamp flashes. If it does not flash, the cap is defective and
should not be used.
If using the galvanometer, a wide deflection of the needle indicates the cap is satisfactory. If there is no
deflection, the cap is defective and should not be used.
Shunt the lead wire immediately after testing.
Splice the blasting cap lead wires to the firing wire, and insulate the wires. Both the blasting cap lead wires
and the firing wire leads must have insulating material stripped from the ends for about three inches in order
to prevent a possible misfire.
Blasting Machines. Blasting machines are used to provide the electrical impulse needed in an electric firing
system. The term used in many NATO countries for blasting machine is "exploder" or "dynamo exploder." There
are six models that derive their power directly from a shunt-wound generator. There are two models, the M32 and
the M34, that derive their power from an alternator and use a capacitor discharge output circuit. The generator-
type machines are actuated by means of a gear-driven armature. The 10-cap machines have metal cases and twist-
type drive handles. The higher-capacity (30-, 50-, and 100-cap) machines have varnished or painted wood cases
and plunger-type handles. The 10-cap and 50-cap machines are used most often.