TM 5-683/NAVFAC MO- 116/AFJMAN 32-1083
Figure 13-5. Diagram of megohmmeter connections.
Therefore discharge capacitance both before and af-
(2) If disconnecting the equipment from the cir-
ter any testing by short circuiting or grounding the
cuit cannot be accomplished, then inspect the in-
equipment under test.
stallation to determine what equipment is con-
nected and will be included in the test. Pay
(5) Apply safety grounds.
particular attention to conductors that lead away
(6) Generally, there is no fire hazard in the
normal use of a megohmmeter. There is, however, a
from the installation. This is very important, be-
hazard when testing equipment is located in inflam-
cause the more equipment that is included in a test,
the lower the reading will be, and the true insula-
mable or explosive atmospheres. Slight sparking
may be encountered when attaching test leads to
tion resistance of the apparatus in question maybe
equipment in which the capacitance has not been
masked by that of the associated equipment.
completely discharged or when discharging capaci-
(3) Test for foreign or induced voltages with a
VOM (para 13-2). Pay particular attention once
tance following a test. It is therefore suggested that
again to conductors that lead away from the circuit
use of a megohmmeter in an explosive atmosphere
being tested and make sure they have been properly
be avoided if at all possible. If testing must be con-
disconnected from any source of voltage.
ducted in an explosive atmosphere, then it is sug-
(4) Large electrical equipment and cables usu-
gested that test leads not be disconnected for at
ally have sufficient capacitance to store up a dan-
least 30 to 60 seconds following a test, so as to allow
gerous amount of energy from the test current.
time for capacitance discharge.