Ground Disconnect; Circuit Breaker Handling Wheels; Racking Mechanism - Siemens SGIM-3268H Manual

Figure 30: Breaker Interlocks and Ground Disconnect.
Figure 31: Racking Mechanism and Floor Interlocks.
Courtesy of NationalSwitchgear.com
Interrupter/Operator Description

Ground Disconnect

Figure 30 shows the ground disconnect contact mounted
at the bottom of the circuit breaker. The spring loaded
fingers of the disconnect contact engage the ground bar
(Figure 31) at the bottom of the switchgear assembly. The
ground bar is to the right of the racking mechanism,
shown at the bottom center of the switchgear.

Circuit Breaker Handling Wheels

The GMI circuit breaker is designed for easy movement
into and out of the metal-clad switchgear assembly. A
section of indoor or Shelter-Clad switchgear does not
require a transfer truck or lifting truck for handling of the
circuit breaker when all circuit breakers are located in the
lower cells. Once the circuit breaker is racked out of the
switchgear, the unit can be pulled using the handles on
the front of the circuit breaker. The circuit breaker will roll
on its bottom four wheels.
On indoor and Shelter-Clad switchgear with circuit
breakers located in the lower cell, the circuit breaker is
easily rolled out of the switchgear by a single person.
When circuit breakers are located in the upper cells,
handling of the circuit breakers requires the use of a hoist
or crane. These lifting devices are also required for removal
of the lower circuit breaker of non walk-in type outdoor
switchgear.

Racking Mechanism

Figure 31 shows the racking mechanism in the switchgear
used to move the circuit breaker between the Disconnect,
Test and Connected positions. This mechanism contains a
set of interface blocks that mate with the bottom of the
circuit breaker housing, and lock the circuit breaker to the
racking mechanism during in and out movement. A
racking handle (not shown) mates with the threaded shaft
of the racking mechanism. Clockwise rotation of the crank
moves the breaker into the switchgear, and counterclock-
wise rotation removes it.
The racking and trip-free interlocks provides several essen-
tial functions.
1. They prevent racking a closed circuit breaker into or out
of the switchgear assembly.
2. They discharge the closing springs whenever the
circuit breaker is inserted into, or withdrawn from, the
switchgear.
3. They prevent closing of the circuit breaker unless it is
in either the Test of Connect positions.
The rating interlock prevents insertion of a lower rated
circuit breaker into a cubicle intended for a circuit breaker
of higher ratings.
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