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 MIL-HDBK-1023/4
(2) Figure 44 illustrates the megger connection to the load and ground for testing
load wire L2. Notice that a manually inserted ground has been connected to the load at the
circuit midpoint.
INSERTED GROUND LOCATION 1
OPEN
L1
L2
WIRENUT
<100M
0
= ON
= DIM
= OFF
GROUND
MEGGER
Figure 44
Sectional Isolation Method - Megger Confirms Continuity Between L2 and Inserted Ground
(a) Testing the circuit, as illustrated, proves that the load cable L2 is intact
between the vault and the inserted ground at the field midpoint. We have learned that the open
fault lies between the inserted ground and the vault along long cable L1.
(b) Now that we have established that the open fault is along L1 between the
vault and the inserted ground, we can begin to track down the fault location further. We have
disconnected L2 and swapped the megger to the L1 cable. Testing the circuit confirms that the
open fault is indeed between the vault and the inserted ground.
(c) The inserted ground is moved to location 2, dividing the L1 cable between
the vault and location 1 in half. Testing the circuit confirms that the cable between vault and
location 2 is good. The open fault location has now been reduced to the cable between ground
location 1 and location 2.
(d) We continue to divide the suspect section of the load circuit in half by
moving the inserted ground to location 3. Testing the circuit confirms that the cable between the
vault and location 3 is good. The open fault location has been reduced to the cable between
ground location 1 and 3.
111
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