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 MIL-HDBK-1023/4
c) Troubleshooting. With the suspect regulator connected to shorted load, check that
output current levels are within tolerance. Use an RMS ammeter to measure the regulator output
current in each brightness level. Check the regulator nameplate for current level specifications.
(1) If the regulator output levels are acceptable in a shorted load, and low when
connected to the circuit, then an overload exists in the series circuit.
(2) Check with maintenance personnel and contractors to determine if anyone has
been working on the overloaded circuit or on the airfield circuits in general. If so, drive the
circuit. Check for the addition of new load circuits. Also, check load intersections for cross-
connected loads.
(3) If no work has been done on the suspect circuit, megger the load and repair
grounds, if present.
(4) Check for and replace bad lamps on the effected circuit. Also, look for dim or
dead sections of the circuit that might indicate grounds or grounded opens.
(5) If a new circuit section has been installed and is connected to the proper circuit,
let the supervisor know that the additional load has overloaded the circuit and that a bigger
regulator is needed.
d) Cause. The most typical reason for an overload is the addition of new load(s) to an
existing circuit. With the addition of new load(s), the total load is now exceeding the rated load
of the regulator. Other common causes for overloaded regulators are:
(1) Cross connecting in another series circuit by accident.
(2) Large percentage of circuit lamps out, generally more than 30% of the regulator
wattage rating.
(3) Multiple grounds or grounded opens on suspect circuit.
(4) Several loose connector kits, bad crimps or bad splices.
6.8
Input Power Circuits
6.8.1
Input Power Circuit Fault Isolation. This section contains step-by-step procedures for
locating faults in the input power circuit. Be certain that no one is working on or near a
de-energized circuit before attempting to energize it.
a) In checking the input voltage, first check the operation of lights or other equipment
in the vault that are connected to the same phase of power. If the lights or other equipment on
this circuit do not operate, the input power circuits are not energized.
b) If the lights and other equipment on this circuit are operating, set the switches,
relays, and contactors in the required position for energizing the regulator.
(1) Check for hum and vibration of the input transformer of the regulator as the
remote-control oil switch, the input switch, or the main contactor is momentarily placed in the
manual "ON" position and then returned to "OFF" or "AUTO" position.
(2) If the energizing controls cannot be set for energizing the regulator, the
energizing controls have failed.
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