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14-1 Introduction
The breaker cubicle sub-assembly is normally
the existing Magne-blast stationary housing for
the removable breaker unit. It contains the pri-
mary disconnects, elevating mechanism, buses,
current transformers, and secondary control
wiring.
14-2 Description of Major
Components
1. Breaker Enclosure
The existing Magne-blast enclosure consists of
a compartment with a hinged door or panel. Ter-
minal blocks, fuse blocks, and some control
devices are mounted inside the enclosure on
the side sheets.
2. Breaker Elevating Mechanism
The elevating mechanism is designed to raise
the breaker unit into the operating position and
to lower the breaker to the disconnected posi-
tion. It consists of a motor, heavy duty jack
screws, jack nuts, and a carriage frame. Rails
are built into the breaker frame to guide it into
position. By means of interlocks, the breaker
cannot be lowered or raised until it has been
tripped. The breaker contacts can only be closed
when the breaker is in the connected position.
For more detail, refer to Chapter 4.
3. Primary Disconnects
The primary disconnect devices utilize silver to
silver contacts to insure against reduction of
current carrying capacity due to oxidation of the
contact surfaces. These contacts are of the high
pressure line contact tube and socket design,
the tube being backed up by heavy garter springs
to insure contact pressure.
4. Buses
The main buses are enclosed in a metal com-
partment with removable covers to provide ac-
cessibility. The buses are supported by flame
retardant, track resistant, glass laminate insu-
lating material and porcelain, which is practi-
cally impervious to moisture, and an excellent
dielectric. No additional coating is necessary.
The bus insulation is an extruded thermoplas-
tic insulation sleeve, suitable for 105 degree C
operating temperatures. The bus bars are in-
serted into the sleeves leaving only the bolted
joints exposed. The bus terminates before and
after the breaker unit. Current transformers may
be located along the bus, on either side of the
breaker, for control applications.
Courtesy of NationalSwitchgear.com
PowerVac
Chapter 14. Stationary Cubicle Subassembly
5. Breaker Testing Provisions
Optional provisions for testing the breaker unit
after removing it from the cubicle can be fur-
nished. The test equipment can be located on
a panel adjacent to the breaker compartment. It
consists of a test coupler to provide control
power to operate the breaker, and push buttons
to trip and close the breaker electrically.
6. Connections
The main bus bars and other connection bars
are made of copper, and the contact surfaces
are silver plated. All field assembled joints in
the primary conductors should be made as fol-
lows:
1. Wipe silver clean with a clean cloth and
denatured alcohol. If badly tarnished, use
a non-abrasive silver polish. Do not use
steel wool, sandpaper, or any abrasive on
the silvered surface. Avoid handling of
cleaned surfaces as much as possible.
2. After cleaning, apply a light of coating of
grease, 0282A2048P009, to the silvered sur-
faces so that the contact area will be thor-
oughly sealed. Using a standard washer,
lock washer, and nut, together, tighten
joints to the torque values shown below.
BOLT CONNECTION TIGHTENING
7. Ground Connection
A ground connection is made between the
breaker ground shoe and the compartment
ground bus.
8. Door Alignment
The exisitng Magne-blast compartment should
have been properly adjusted and leveled dur-
ing the orginal installation. Proper door align-
ment can be verified as follows.
The top of each door should be level with the
adjacent doors; the sides of each door plumb;
the surface of each door flush with the adjacent
door; and, the space between adjacent doors
equalized to permit their free swing and present
a neat appearance. The door stops should be
adjusted to permit a door swing of approximately
105 degrees.
53
®
5kV Vertical Lift
Bolt Size
Torque
1/2 x 13
50 - 60 foot pounds
5/8 x 11
60 - 70 foot pounds
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