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 MIL-HDBK-1023/4
f) Ground Return Method. The ground return method is similar to the intentional
ground method with one big exception. The ground return method is very good for detecting and
locating grounds faults and opens of all resistance levels. However, the ground return method is
a much more aggressive route to take in troubleshooting load circuits. The risk to regulator,
isolation transformers, connector kits and cable is higher than with the intentional ground
method. There are times when using the ground return method is warranted, but indiscriminate
use of this method should be discouraged.
(1) The "Ground Return Method" connects a #8 AWG cable to one side of the
regulator output, as does the intentional ground method. However, the exception is that the
"Ground Return Method" disconnects the grounded side of the regulator output from the load,
allowing only one path, through the ground, for the current on the grounded side of the regulator
to flow. Due to the open nature of the load at start up, this arrangement causes the regulator to
produce higher voltages on the output. Until the current strikes over to the fault, the regulator is
in an open circuit condition. The regulator may likely trip out in an open circuit condition if the
fault resistance is too high.
(2) Do not persist in cycling the regulator through open circuit trip outs.
(3) The "Ground Return Method" is not recommended for regulators with 2400
volt or 4160 volt inputs due to the stress open circuits place on the internal primary switch.
(4) Revert to other means of fault isolation if the regulator trips off or has a 2400
volt or 4160 volt input. The "Ground Return Method" may also transform high resistance
grounds in cable, connectors, and transformers into low resistance grounds or smoking holes in
the ground. The reader is advised that this method is aggressive, and hard on equipment.
(5) This troubleshooting method should be reserved for cases where the
"Intentional Ground Method" has been tried and is not producing the desired results. High
resistance to ground type opens and high resistance ground faults would be typical applications
for the "Ground Return Method."
(a) Figure 27 illustrates a regulator and load with a typical S1 cutout (S1-A)
and an S1 arranged as a "Ground Return Switch." Notice that if the ground return switch handle
is removed, the L2 line will be grounded, and direct continuity with the load will be broken.
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