18
Key interlock description
Test port interlock:
l
Locks test port closed in preparation
for a grounding operation
l
Key works in the key transfer interlock.
For device types B and D, the test port key
interlock must be operated as the first step
in preparing the device for a grounding
operation.
This interlock functions to lock closed those
test ports associated with primary
disconnects which are not to be grounded,
and assures that the voltage tests prior to
grounding are made only at the primary
conductors which are to be grounded. This
helps avoid accidental grounding of a live
circuit.
Key transfer interlock:
l
The key transfer interlock is not
accessible when the ground and test
device is inside the circuit breaker cell.
l
The decision to ground must be made
before inserting the ground and test
device into the circuit breaker cell.
l
Accepts key from the test port interlock
to allow removal of the key that works
in the selector switch interlock to
enable the grounding procedure.
The key transfer interlock is positioned on
the top of the ground and test device to
require that the decision to ground or not to
ground be made before the ground and test
device is inserted into the circuit breaker
cell.
When the device is in the circuit
breaker cell, the key transfer interlock in not
accessible.
With the ground and test device withdrawn
from the circuit breaker cell, the key transfer
interlock becomes accessible to receive the
key from the closed and locked test port key
interlock. Upon inserting this key and
rotating, the second key in the key transfer
interlock becomes available. This second key
functions in the selector switch to allow
selection of the electrical closing
(grounding) or opening functions.
Selector switch
Off position:
l
Control power disconnected
l
Padlockable in this position
l
Key required from key transfer
interlock to operate
l
Trip latch is blocked.
Close position:
l
Requires key from key transfer
interlock to switch to CLOSE position
l
CLOSE position allows execution of
a remote "close" command
l
Trip latch is blocked.
Trip position:
l
Requires key from key transfer
interlock to switch to TRIP position
l
Trip position allows execution of a
remote "open" command.
Selector switch
The selector switch allows selection of
CLOSE, OFF or TRIP (open) functions.
Mechanically, it blocks the ground and test
device trip latch in the CLOSE and OFF
positions.
Electrically, while in the OFF position, it
removes the spring charge, close and trip
functions from the control circuit. In the
CLOSE position, it enables those portions of
the circuit which support spring charging
and closing (spring release). In the TRIP
position, only the tripping circuit is enabled.
The second key from the key transfer
interlock, when applied in the selector
switch interlock, will free the switch for use.
The selector switch is locked by the key in
the OFF position, and may be padlocked in
this position as well.
