> Yahoo! is not affiliated with the authors of this page or responsible for its content.
External Accessories
73
External Accessories
External accessories make circuit breakers suitable for specific
applications. A variety of external accessories are available.
Rear Connecting Studs
Rear connecting studs are used for switchboard mounting of
circuit breakers. Rear connecting studs are available in various
lengths of either bus or cable connections.
Rocker Arm Assembly
The rocker arm assembly is used to mechanically interlock two
adjacent circuit breakers of the same frame configuration. Both
circuit breakers can be open at the same time, but this allows
only one breaker to be closed at any time. 74
Max-Flex
The I-T-E® Max-Flex flange-mount handle operator is a flexible
cable control device used for remote switching of a circuit
breaker within an enclosure. The flexible cable is connected
directly to the breaker switch handle at one end and a factory
installed switch at the other end. The remote handle operator
located on the enclosure is used to perform mechanical open/
close switching operations. The cable comes in standard 3 or
4 foot lengths, however, lengths up to 20 feet can be ordered.
When using a standard circuit breaker handle extension, it
is necessary to exactly align the breaker with the extension.
With the Max-Flex handle operator this exact alignment isnt
necessary. 75
Telemand® Electric
The I-T-E Telemand® electric motor operator is designed to
Motor Operator
open, close, and reset a circuit breaker by remote control. It is
mounted on the face of the circuit breaker so that it can engage
the breakers operating handle. The built-in motor is connected
to remote pushbuttons. Pressing the ON pushbutton causes
the electric motor to move the circuit breaker to the ON
position. Pressing the OFF pushbutton causes the electric
motor to move the circuit breaker to the OFF position. To
reset the circuit breaker from the tripped position, press the
OFF pushbutton to move the handle to the OFF position.
Then press the ON pushbutton to the close the breaker
contacts. 76
Plug-In Assemblies
Plug-in mounting assemblies provide means for a quick change
out of circuit breakers and molded case switches without
disturbing the power connections.
Terminal Connectors
Various terminal connectors are available to permit easy front
connection of either copper or aluminum insulated conductors
to the terminal of a circuit breaker or molded case switch.
Terminal connectors are designed and tested to accommodate
the conductors or requirements outlined within the related UL
standards. 77
Handle Blocking Device
A handle blocking device is a non-lockable device that may be
added to a circuit breaker to secure the handle in either the
ON or OFF position. The device slides into slots provided
on the circuit breaker. This device prevents accidental operation
of the handle. The device will not prevent the circuit breaker
from tripping when blocked in the ON position. The following
illustration shows the handle blocked in the ON position.
Handle Padlocking Device
The handle padlocking device is used to padlock the circuit
breaker in the ON or OFF position. The device mounts over
the handle and a customer supplied padlock is used to lock the
handle. The breaker will still trip if locked in the ON position.
Locking Device
Padlock 78
Ground Fault Sensor
An external ground fault sensor is available for the ED frame
circuit breakers. The relay functions to de-energize a circuit
within an established period of time when the current to ground
exceeds a predetermined value. This is done by detecting a 5
mA ± 1 mA or 30 mA ± 6mA current difference between two or
more load conductors passing through the sensor.
Sensor
Review 6
1. A ____________ - ____________ option is used when it
is necessary to trip a breaker from a remote location,
but cannot be used to reset the breaker.
2. An ____________ ____________ device is used to
automatically trip a circuit breaker when the supply
voltage drops.
3. The advantage of the Max-Flex flange-mount handle
operator versus a handle extender is that ____________
____________ isnt necessary.
4. A ____________ ____________ is used to prevent two
adjacent circuit breakers from being ON at the same
time.
5. ____________ - ____________ mounting assemblies
provide a means for a quick change out of circuit
breakers without disturbing the power connections. 79
Insulated Case Circuit Breakers
The discussion to this point has been on molded case circuit
breakers. Another type of circuit breaker is the low voltage air
circuit breaker. Instead of having a molded case, the operating
mechanism of a low voltage air circuit breaker is assembled
on a metal frame for use in switchboards and switchgear.
The components of a low voltage air breaker are larger
and heavier for severe duty applications. Unlike molded case
circuit breakers, low voltage air breakers have high short time
withstand capabilities (breakers ability to ride through a short
circuit event). Molded case circuit breakers, on the other hand,
have high interrupting ratings. A circuit breaker was needed that
could supply high short time withstand and high interrupting
ratings. Insulated Case circuit breakers (ICCBs) were designed
to fill that need. 80
Ampere Ratings
There are six frames: 800, 1200, 2000, 3200, 4000, and 5000
amps. Interchangeable rating plugs and a continuous current
adjustment are provided with each trip unit. ICCBs can be
applied in applications from 100 to 5000 amps through 600 VAC.
The frame ampere rating is determined by the current sensors
in the breaker.
Interrupting Ratings
ICCBs use color coded labels to clearly identify the interrupting
class of each breaker. A removable rating plug installed on the
trip unit allows a user to select a current rating from 50 to 100
percent of the current sensor value. The following chart reflects
the RMS ampere interrupting rating of Siemens insulated case
circuit breakers. 81
ICCB Electronic Trip Unit
The electronic trip unit uses a microprocessor to execute the
numerous functions programmed in the unit. The adjustments
on the trip unit allow the user to select which values are to
be used by the microprocessor in performing its protective
function. 82
Interchangeable
The trip unit is designed to use field interchangeable rating
Rating Plugs
plugs. Rating plugs allow the effective ampere rating of the
circuit breaker to be modified within a range of 50-100 percent
of the breakers frame ampere rating.
The interchangeable rating plug is located at the top of the
electronic trip unit.
Principle of Operation
Current is derived from current sensors (transformers) mounted
in the breaker. The current signals from the transformers are
converted to digital values in the trip unit. The electronic trip unit
monitors current levels at an equivalent sampling rate of 353
samples per cycle per phase. It then decides when the circuit
breaker should be tripped due to an overcurrent condition. A
magnetic latch in the circuit breaker causes the breaker to trip
when it receives a trip command from the electronic trip unit.
Sense
Decide
Act
Current
Transformers
Electronic Trip Unit
Magnetic Latch 83
Continuous Amps and
The continuous ampere adjustment sets the current level at
Long-Time Delay
which the breaker will continuously operate without tripping.
For example, if a rating plug is 2000 amps and the continuous
ampere adjustment is set to 50%, the breaker will continuously
operate at current levels up to 1000 amps.
The long-time delay adjustment is used to set the tripping delay
of the circuit breaker based on the magnitude of the overcurrent
condition (6 times Ir). For example, if the rating plug is 2000
amps and long-time delay is set to 10 seconds, a fault current
of 12,000 amps (6 x 2000) will cause the breaker to trip after 10
seconds. Long time is an inverse I
2
T ramp function. This means
the higher the current, the shorter the time the circuit breaker
will remain ON.
Short-Time Pickup and
The short-time pickup adjustment is used to set the level of
Short-Time Delay
high current the breaker will carry for a short period of time
without tripping. This adjustment is set in multiples of the
value of the rating plug (Ir). Together with short-time delay, this
adjustment allows downstream breakers time to clear short
circuit faults without tripping upstream breakers. Short-time
delay is used to set the time interval the breaker will wait
before responding to the current value selected by short-time
pickup. There are two modes of operation: fixed and I
2
T. The
I
2
T delay has the characteristic of being inversely proportional to
the square of the magnitude of the current. This means higher
overcurrent c