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 MIL-HDBK-419A
4 . 4 TEST EQUIPMENT. Test equipments are available to measure the resistances and impedances of the fault
protection subsystems including the grounding (green) conductor as well as the signal reference subsystem
(equipotential plane) which may at times become part of the fault protection subsystem. These equipments can
measure the impedances (at 60 Hz) of each path from the equipment having the fault to the first service
disconnect means and therefore assist in determining the value of the fault current over each path. The
information will in turn be beneficial in determining or predicting the degree of interference which may be
anticipated should a fault current be superimposed on the signal reference subsystem. (4-1 and 4-2)
NOTE: Lift when single transformer supplies power to
more than one building or
because of objectionable current, noise or interference.
Figure 4-3. Three-Phase 120/208 Volt AC Power System Ground Connections
4-5
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