Biddle MEGGER - Page 14

Apparatus Under Test Must Not Be Live
See page 10, on Preparation of Apparatus for Test.
If neutral or other ground connections have to be discon-
nected, make sure they are not carrying current at the time, and
that when disconnected no other equipment will lack necessary
protection.
Pay particular attention to conductors that lead away from
the circuit being tested and make sure they have been properly
disconnected from any source of voltage.
Shock Hazard from Test Voltage
Observe the voltage rating of the “Megger” instrument and
regard it with appropriate caution. Large electrical equipment
and cables usually have sufficient capacitance to store up a
dangerous amount of energy from the test current. Make sure
this capacitance is discharged after the test and before han-
dling the test leads.
Explosion and Fire Hazard
So far as is known, there is no fire hazard in the normal use
of a “Megger” Insulation Tester. There is, however, a hazard
when testing equipment located in inflammable or explosive
atmospheres.
Slight sparking may be encountered: (1) When attaching
the test leads to equipment in which the capacitance has not
been completely discharged. (2) Arcing through or over faulty
insulation during a test. (3) Discharge of capacitance follow-
ing a test.
Suggestions
DO NOT USE THE INSTRUMENT IN AN EXPLOSIVE
ATMOSPHERE.
For (1) and (3): Arrange permanently installed grounding
facilities and test leads to a point where instrument connections
can be made in a safe atmosphere.
For (2): Use low voltage testing instruments, or a series
resistance.
For (3): Do not disconnect the test leads for at least 30 to
60 seconds following a test, so as to allow time for capacitance
discharge.
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