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 MIL-HDBK-1023/4
(4) See Figure 42. In the third test we narrowed the suspect area of the circuit
down to about nine lights, leaving the intentional ground on the regulator where it is (since it is
conducting to the load). We move to manual ground #3 at the remaining suspect area midpoint.
Turning on the regulator we have five more lights operating and have narrowed our suspect area
for the open to four fixtures. If we were to pursue this further, we would cut the suspect area in
half again and again until we found the open.
OK
OK
OPEN.
SUSPECT AREA.
OK
KNOWN GOOD
= ON
CIRCUIT
KNOWN GOOD
= DIM
CIRCUIT
= OFF
L1
L2
ON
REGULATOR
GROUND.
DIVIDE SUSPECT AREA OF LOAD IN HALF WITH MANUAL GROUND #3.
IN FOUR TESTS OPEN HAS BEEN ISOLATED TO A FOUR FIXTURE AREA.
Figure 42
Ungrounded Open on Load Circuit Manual - Ground Test Fourth Test
f) The sectional isolation method for locating opens in series circuits is very similar to
the intentional ground method discussed earlier in this text. As in the intentional ground method,
a manual ground is inserted into the load circuit, and earth ground provides a return path for our
tests. However, a megger is used to locate the open in the load rather than a regulator as in the
intentional ground method.
109
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