TM 9-1375-213-12
27. Testing Electric Wires, Blasting Caps and
Circuits
a. Testing Firing Wire. Test firing wire while
on reel for serviceability. After wire is unreeled,
test it again for any damage caused during un-
reeling and laying of wire.
(1) When using blasting cap test set M51:
(a) Check test set by connecting posts with
should flash when handle is squeezed.
(b) Separate firing wire conductors at both
ends.
(c) Connect pair of firing wire conductors
at one end to test set binding posts.
(d) Actuate test set. Indicator lamp should
not flash. If it does, firing wire has a short circuit
(e) Twist wires together at one end, and
connect those at other end to test set posts.
Actuate test set. Indicator lamp should flash. If it
does not flash, firing wire has a break and is un-
serviceable.
(2) When using galvanometers:
(a) Check galvanometers by holding a piece
tery is good, and battery connections are clean,
this should show a wide deflection of needle, ap-
proximately 25 units. Galvanometers can be used
to closely check circuits and components only if
battery is good and its connections are clean.
dle does not give a full deflection on shorting of
terminals.
(b) Separate firing wire conductors at both
ends, and touch those at one end to galvanometers
posts. Needle should not move. If it does. firing
(c) Twist wires together at one end and
Connecting wires (usually annunciator wire) are
touch those at other end to galvanometers posts.
used when distance between blasting caps is
This should cause a wide deflection of needle. No
greater than length of usual cap lead wires.
movement of needle indicates a break; a slight
b. Leapfrog Series. The leapfrog method of con-
which may be caused by a dirty wire, loose wire
necting charges in series (B, fig. 210) is useful
connections, or wires with several strands broken
for firing ditching charges or any long line of
off at connections. Make sure conductors at blast-
charges. It consists of omitting alternate charges
ing machine site stay twisted together.
on the way and then connecting them to form a
b. Testing Blasting Cap.
return path for the electric impulse to reach the
other lead of firing wire, This brings both end
WARNING
wires out at the same end of the line of charges,
Before removing shunt and before test-
and thus eliminates laying a long return lead from
the far end of the line of charges back to the
place cap in a hole, behind a barricade,
firing wire.
or under a sandbag. Unroll so that cap is