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Figure 3-9. Vent valve.
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TM-5-6120-250-12 Substation Trailer Mounted 500 KVA AC 4160-416Y/240V 208Y/120V 3 Phase 50/60 Hertz Manual
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Figure 3.10. Racking of a circuit breaker
Section VII. MAINTENANCE OF LOW VOLTAGE SECTION
3-13. General
(load break switch) and control sources
Instructions contained in this section are for operator's
have been disconnected. See paragraph 2-
information and guidance in maintenance of the low
13 c.
voltage switchgear section.
3-15. Circuit Breakers (Main and Feeder)
WARNING
a.  Inspection of the circuit breaker is recom-
Before any covers are removed or doors
mended at least once a year.  More frequent in-
opened which permit access to the primary
spections are recommended if severe load conditions,
or secondary circuits it is essential that the
dust, moisture or other unfavorable conditions exist. If
the breaker remains open or closed for a period of six
circuits be de-energized. See paragraph 2-
months it is recommended to open and close it several
13.
times in succession, preferably under load. A complete
inspection of the breaker including contacts and are
3-14. Enclosure
quenchers should always be made after the breaker has
a.  Check and inspect all devices, doors, latches
interrupted a short circuit. It should be operated slowly
and hinged panels to see that they are functioning
manually to observe the contact alignment and to make
properly. Check mounting of devices and see that all
sure all mechanical parts move freely without binding or
electrical connections are tight.
excessive friction.
b.
Check mechanical indicating devices and
b.  The breakers are furnished with a drawout
interlocks.
mechanism which facilitates the inserting and with-
drawing of the breaker from its enclosure. It provides a
c. Check that all bus mounting bolts and splice
suitable means of forcing the breaker through each part
connection bolts are tight.
of the inserting and withdrawal operations. The drawout
mechanism is equipped with a drawout trip interlock
d.  Wipe and vacuum  clean the busses and
which  prevents  a  racking  operation  from  being
supports.
performed when the breaker is closed. To withdraw a
breaker perform the following steps.
e. Inspect all main cable connections for signs of
overheating. and tighten all connections.
(1) Trip the breaker (push trip button) to release
the positive racking interlock.
f.  Check that all 120 volt wiring connections are
tight and intact.
(2) Lifting the racking handle (view E fig. 3- 10)
as far as it will go. (This operation will re- engage the
g.  Check  the  ground  bus  connections  and
trip interlock to hold the breaker trip- free for the
mounting bolts for tightness and clean ground bus.
remainder of the withdrawal racking operation.
h.  Check to see that all anchor bolts and other
(3) Reset the handle to its lowered position and
structural bolts are tight.
lift it again. This operation must be performed 5 times
to completely disengage the racking cams (view A) from
i. Thoroughly clean interior of compartments. Use
their racking pins in the compartment.  After the fifth
a vacuum cleaner and clean rags only. Do not use
lifting stroke (view I) let the handle drop to its connected
steel wool or oxide papers. Blowing with compressed air
position, (View G).
is not recommended.
(4) Pull the breaker out of its compartment until
j.  Clean and inspect all painted surfaces and
the test position stop (view C) engages to hold the
retouch where necessary.
breaker in "test position".
k.  Clean air filters as described in preceding
(5) Depress the test position stop handle (view
D) and pull the breaker out of its compartment as far as
WARNING
the drawout tray will travel.
Before inspection or any maintenance work
is done be sure the breaker is in the open
position. All electrical power both primary
3-16

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