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 MIL-HDBK-1023/4
(c) Figure 31 illustrates the further testing of the grounded load section
discovered in Figure 30. The grounded load section is divided up into four subsections by
manually opening the grounded load section in three more locations, creating four subsections
from the grounded load section.
TEST 3
TEST 1
TEST 2
TEST 4
GROUND FAULT
MANUAL OPENS
LOAD IS DISCONNECTED FROM REGULATOR
= ON
= DIM
= OFF
Figure 31
Sectional Isolation Method - Megger Tests Locate Grounded Section of Load
(d) During the megger tests 1 through 4 each subsection is megger tested to
ground. Tests 1, 2, and 4 passed without indicating ground. However, test 3 failed indicating
that the ground is within the two-fixture length of cable and transformer installations tested in
test 3.
(e) Direct investigation of the failed circuit should reveal the ground. If no
apparent faults can be located, the remaining portion of the grounded circuit could be subdivided
again.
6.5
Locating Ungrounded Shorts in Field Circuits
6.5.1
Isolating Ungrounded Shorts. When ungrounded shorts are indicated, an initial
analysis should be made by energizing the circuit and visually determining which lights are
operating. Then, the fault may be further isolated by using a clamp-on ammeter or performing
the following circuit analysis test.
95
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