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 MIL-HDBK-1023/4
a) Symptoms. Short within load: Regulator operates normally, but entire sections of
the load are out, or all of the load is out. Megger tests of load circuit may or may not reveal
grounds on circuit.
Short cross connecting loads: Operating one regulator in vault causes another regulator to trip
out or malfunction in some way. Ammeter on regulator in the "off" position indicates current.
Lights on a circuit that should be off are on "dim" when another regulator is operating.
b) Troubleshooting. Short within load: If grounds are present on load circuit,
troubleshoot as if it were a ground. If grounds are not present and some lights are on, investigate
transition points in load between lights that are working normally and lights that are not.
(1) If no lights are coming on and the regulator is working normally on the
suspected load, the short is in the home run between the load and the regulator.
(2) Short cross connecting loads: Drive the circuit and look for lights that are out
or dim. Investigate those points where the lights change intensity.
(3) Megger between various load circuits looking for continuity, regulator 1 load to
regulator 2 load, etc. With all other regulators off, turn on the regulator with the suspected short.
If the current is detected on an "off" regulator load or continuity is measured between loads,
measure all other regulator outputs for current with clamp-on ammeter. Then, loads can be cross
connected in an effort to find the cross connection.
c) Causes. Shorts in airfield loads are usually caused by heat from a grounded cable
or bad connection burning away or melting insulation on an adjacent cable, shorting the two
together.
(1) Figure 32 illustrates what happens when the load becomes shorted to itself.
Note the lights are dim after the short in the load, and may be off altogether if the remaining
portion of the load, after the short is long. The short may or may not be grounded and have the
same effect, if no other grounds exist on the circuit. Again, driving the circuit and "taking a
look" will locate the problem.
d) Circuit Integration Method. The circuit integration method is very useful in
locating load circuit to load circuit shorts. This load-to-load short condition is usually
discovered by one of the following: load-to-load resistance tests, visual abnormalities in the
load, reports of voltage present on "off" regulators or load circuits, investigations into unusual
regulator behavior.
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