I. B.
35-
240-1
TYPE DB-75
DE-ION AIR CIRCUIT BREAKER
The overcurrent tripping device can be re
m oved from the breaker easily and replaced
with another unit of the same or different
r ating without affecting the calibration of
the units involved.
Construction
The mounting frame casting supports the
two sub-assemblies of the trip unit.
On the
upper part of the frame are the two magnetic
a rmatures a nd their associate d links a nd
brackets.
Fastened to the lower part of the
mounting frame is the moldarta box which con
tains the calibration springs, time delay ele
m ents and calibration knobs.
This box is
held to the mounting frame by two long screws
at the bottom of the calibration box.
Installation and Removal
CAUTION:
BEFORE REMOVING OR INSTALLING A
TRIPPING DEVICE, BE SURE THAT THE BREAKER IS
IN THE OPEN POSITION AND DE-ENERGIZED
To remove an overcurrent tripping device
from the breaker, loosen the two captive bolts
at the bottom of the mounting frame (L-3) un
til they turn freely.
Then loosen the two
bolts at the top of the mounting frame while
supporting the trip unit so that it doe� not
fall.
These two bolts clamp a slotted angle
mounting bracket and merely have to be loos
ened; they do not have to be removed from the
mounting frame.
The trip unit is then free
to be removed from the breaker by lowering it
down behind the breaker platform.
To install a tripping device on a breaker,
first make certain that the breaker is open
and is not connected to live circuits.
Then
loosen the upper mounting bolts on the trip
u nit so that the bolts can slide into the
slotted mounting brackets on the stationary
yoke.
Then install the trip unit from the
b ottom of the breaker, sliding it up behind
the mechanism platform.
Start the bottom two
c aptive mounting bolts, but do not tighten
completely.
Next, align the trip unit so
that the gaps between the tapered portions of
the main armature are approximately equal
when the main armature is closed. Then tighten
all four mounting bolts securely.
Adjustment of Trip Screw
The trip screw mounted on the trip finger
must be adjusted properly to obtain proper
tripping.
CAUTION:
SINCE THIS ADJUSTMENT INVOLVES
TRIPPING THE BREAKER, CARE MUST BE TAKEN TO
KEEP FINGERS AND FACE AWAY FROM ALL CONTACT
ARMS AND OPERATING LINKAGE.
To proceed with
the adjustment, turn the long time dial a t
the bottom o f the calibration b o x counter
clockwise to the stop so that the trip unit
is set for minimum time delay.
Then close
the breaker and carefully reach under the
mechanism with both hands and push the lower
armature fully closed with the thumbs.
Hold
it closed for at least the minimum long delay
time
(20
to
4 0
seconds) .
If the bre ak e r
t rips, reset the screw at t h e e nd o f the
tripping finger until the breaker just barely
trips.
Before re-adjusting the trip screw,
make sure that the breaker is in the o pe n
position.
After finding the position of the
trip screw at which the breaker just trips,
turn the screw exactly one full turn in the
direction to trip the breaker sooner.
Check
to make sure that the breaker will trip when
either armature is closed if long and instan
taneous type trip units are used, or when
both armatures are closed if .long and short
delay type trip units are used.
The short
delay armature is for timing only.
Closing
it alone will not trip the breaker.
Operation
STANDARD OVERCURRENT T RIPPING DEVICE
(Refer to Figure 7A)
When a small, overload current flows through
the breaker pole unit conductor (R) . it causes
the moving armature
(B)
to be attracted toward
the stationary core (A) .
The motion of the
armature is retarded by the diaphragm (D) whose
motion is in turn controlled by the amount of
air admitted by the long time delay valve (F) .
After a time delay, determined by the setting
of valve (F) , the armature will have rotated
the trip crank
(J)
far enough to trip the
breaker by moving the trip lever (K) .
During
this type of tripping, the compression spring
(C) is not compressed beyond its normal length.
15
www
. ElectricalPartManuals
. com
