Table 4-2. Unit Troubleshooting Guide (Continued)
TEST OR INSPECTION
2. Distribution pump motor hums but wont turn (Reference Schematic Diagram FO-1, Sheet 5, schematic tines
Step 1. Check generator voltage on all three phases. it must be 435/445 VAC on each phase.
(a) Adjust to correct voltage.
(b) If voltage is not correct on all three phases, refer to generator troubleshooting.
Step 2. Check system air pressure and use an air manifold drain valve to lower it blow 1400 psg (9653 kPa).
Turn the air compressor switch on and note if the air compressor turns.
If the air compressor does not operate, notify direct support maintenance.
Step 3. Check continuity, point-to-point, from P19A to J62A, P19B to J62B, P19C to J62C, and P19D to
J62D. Check each lead for shorts between phases and shorts to the ground wire. The reading should
be infinity for each check.
(a) Replace any cable or connector that shows open during continuity checks (paras. 4-27
(b) Replace an cable or connector that shows a short between phases or a short to ground
(paras. 4-27 and 4-33)
(c) Repair any loose or damaged wires in the external electrical panel (para. 4-33).
(d) Replace any MOVS in the external electrical panel that show physical damage or are shorted
to ground from the power terminal (para. 4-33).
Step 4. Tag and disconnect motor leads (T1 , T2, T3 . Set multimeter to Ohms x 1000 scale and connect test
leads between each motor lead and the motor frame. Readings should be infinity for each step.
Replace pump/motor assembly if the meter reading is zero (para. 4-87).
Step 5. Set multimeter to Ohms x 1 scale and check for continuity between all pairs of motor leads T1 and
T2,T1 and T3, T2 and T3. Readings should be zero or near zero for each step.
Replace pump/motor assembly if reading is infinity (para. 4-87).
Step 6. Check motor cable for continuity on each lead and for shorts between phases and ground
(a) Replace the cable if open or shorted (para. 4-87).
(b) Notify direct support maintenance if the above checks have not found the problem.
3. Distribution pump circuit breaker opens whenever distribution pump is started, ROWPU shuts down when dis-
tribution pump is started (Reference Schematic Diagram FO-1, sheet 5, schematic fines 524-526).
Step 1. Check for short circuits.
(a) Shut down the ROWPU. Shut down the generator. Refer to electrical schematic Appx. l-1
and interconnect diagram Appx. I-2. Refer to distribution pump won't start (malfunction 1)
steps 3 thru9.
(b) Notify direct support maintenance.
4. Distribution pump circuit breaker trips open repeatedly, distribution pump ground fault trips open repeatedly
(Reference Schematic Diagram FO-1, Sheet 5, schematic lines 524-530).
This problem is hard to pin point directly as the two circuit breakers are electrically tied together so
that what affects one will usually trip the other even though each is sensing different levels of short
circuit. The direct-acting circuit breaker will only trip when overcurrents exceed its setpoint, such
as a direct bolted short circuit. By contrast, an arcing short circuit may amount to only a fraction of
the direct-acting circuit breaker setpoint and not cause it to trip. Arcing faults are typically caused
by loose connections, the presence of vermin, rodents, and insects in equipment, or insulation de-
terioration, as a result of mechanical damage, heat aging, or moisture, dust, and other contami-
nants. Since the arcing type fault usually involved a flow of current in the ground path, the ground
fault circuit breaker monitors the ground circuit for current flow. When it senses current in the
ground circuit it will trip and also trip out the pump circuit breaker. Under other circuit conditions
balanced, unbalanced, or single-phase load currents, or single or three phase short circuits not
involving ground it will not trip even though the pump breaker does. For these reasons the fol-
lowing troubleshooting steps are very general and success in isolating the problem relies on the
electrician to carefully respect all cables, connectors, and connections for signs of damage or mois-
ture intrusion. In some cases only the substitution of known reliable components will identify the
4-82 Change 1