Electrical
Circuit Breakers
By: L. W. Brittian, Mechanical-Electrical
Instructor
PART 5
IN THIS THE FIFTH PART OF THE ARTICLE
COVERING CIRCUIT BREAKERS, THE FOLLOWING TOPICS ARE COVERED:
• INSULATED CASE
CIRCUIT BREAKERS
• ACCESSORIES
• SHUNT TRIP
• AUXILIARY-REMOTE ALARM SWITCH
• GROUND FAULT SENSOR
• UNDER VOLTAGE TRIP
• LOCK-OUT/TAG-OUT PROVISIONS
• REMOTE OPERATOR HANDLE
• STORED ENERGY BREAKER OPERATOR
INSULATED CASE CIRCUIT
BREAKERS (ICCB)
This type of circuit breaker is assembled on a metal frame
contained within an insulated case and is provided with
air break contacts. These types of circuit breakers are
used as a part of larger installations such as switchboards
and MCC type switchgear. Their components are larger and
heavier for severe duty applications.
The insulated case circuit breaker typically has a high
short time withstand and high interrupting rating. They
are available today with both a local and a remote means
of communication for setting of the various values, and
facilitate such tasks as remote monitoring of electrical
energy consumption and troubleshooting. The insulated case
circuit breaker can be purchased today with any of a growing
list of accessories, several of which are briefly reviewed
in the following paragraphs.
ACCESSORIES
The following is a brief survey of the accessories that
are commonly available for the ICCB and for microcomputer-equipped
circuit breakers today. Only those specific accessories
listed for a specific breaker should be attached to a breaker.
To do other wise may potentially compromise safety.
SHUNT TRIP
Some times it is advantageous to turn a breaker off from
a remote location. To facilitate this task, an accessory
called a shunt trip feature is installed by the manufacture
inside of the breaker. This device consists of an electro-magnetic
trip coil that is connected in series with an external field
wired switch. When the switch contacts are closed, power
is passed to the shunt trip coil causing the breaker’s
mechanical latch to move to the open position. Re-closing
the breaker is done by physically going to the breaker and
manually moving the operating handle to the on–closed
position.
When opened by use of the shunt trip coil, the breaker’s
operating handle moves to the off (maximum handle travel)
and not the tripped (short of full handle travel) position.
Knowing this can help when trying to determine if the breaker
tripped off due to an overcurrent condition or was remotely
turned off.
AUXILIARY-REMOTE ALARM
SWITCH
Occasionally it is advantageous to have an indication that
a breaker is open at a remote location. To facilitate remote
indication, some manufactures provide a built-in form C
(SPDT) contact set. The contact set may receive power from
the breaker’s power source by internal connection,
or it may be a set of dry contacts that require a foreign
power source. By “foreign power source”, I intend
to communicate that the form C-contact set is not powered
from the same source of supply of current going to the breaker’s
line terminals.
GROUND FAULT SENSOR
Some manufactures offer an external ground fault sensor
accessory. These devices open the circuit within a pre-established
time period when the current flow to ground exceeds a pre-determined
value. This occurs by detecting a current difference between
two or more load leads that have been routed through an
air core current transformer. The trip current set point
values are higher for these types of devices than are found
on common MCCB type GFCI (5 to 6 Ma class A) units. This
is because these types of sensors are primarily intended
to provide protection for equipment and not for people.
Be aware that some circuit breakers are provided with a
ground fault trip unit, while others are provided with an
alarm-only function for use with emergency systems as required
by the NEC in sections 700-7(D) and 700-26.
UNDER VOLTAGE TRIP
The undervoltage trip feature will operate the circuit
breaker when the supply voltage drops below a preset value.
Typically the adjustable range provided is from 35 to 70%
of nominal line voltage. This device incorporates a feature
that prevents the breaker from being re-set until the supply
voltage returns to a minimum of 85% of its normal level.
LOCK-OUT/TAG-OUT PROVISIONS
With this factory-installed accessory the task of performing
OSHA required Lock-out/Tag-out of the breaker is made easier
and safer. With the device properly installed and locked,
the breaker handle cannot be moved to the closed position
from the open position.
REMOTE OPERATOR HANDLE
Occasionally a breaker will be installed in a type of enclosure
that does not allow ready access to the breaker’s
operator handle with the door closed. Many manufactures
offer a flexible cable (or rod) that is connected directly
to the breaker’s operator handle at one end and an
externally mounted manual switch at the other end. The remote
operator handle is typically installed on a flange type
section of the enclosure and performs the opening and closing
of the breaker without the need to open the enclosure’s
door. The handle is pre-drilled to allow it to be locked
in the open-off position for safety. This feature helps
to reduce the risk associated with arc related flash burns.
The risk of flash burns has increased as our nation’s
electrical generating, transmission, and distribution capacity
has increased over the years. The 2002 edition of the NEC
has introduced specific requirements intended to reduce
the risk of injury to personnel from electrical arc flash
burns. These handles are sometimes drilled in the field
so that they may also be locked in the on position where
it is determined by the AHJ that safety is enhanced to do
so.
STORED ENERGY BREAKER OPERATOR
The two-step stored energy mechanism is used when a lot
of energy is required to operate the circuit breaker and
when it needs to be closed or opened rapidly to minimize
arcing related damage. The two-step stored energy process
is to charge (compress) the closing spring and then release
the energy to close the breaker. This method uses separate
opening and closing springs. This design permits the closing
spring to be charged independently of the opening process.
Allowing for an open-close-open duty cycle. The closing
spring can be charged manually via a charging handle or
an internally mounted DC electric motor about the size of
a 3/8 inch drill motor. The motor can be operated remotely,
allowing for increased operator safety.
Once the closing spring is charged, it sits compressed
ready to rapidly re-close the breaker. Safety is enhanced
with this type of operating mechanism by providing remote
(motor operated) charging of the spring and then allowing
the breaker to be remotely closed. Should it become necessary,
provisions have been provided by the manufacture for charging
the closing spring manually.
In the next part of this article the following topics will
be covered:
• MOLDED CASE CIRCUIT BREAKERS
• MOLDED CASE CIRCUIT BREAKER MAINTENANCE
If you have any questions or comments, please send me an
E-mail.
Remember Work Smarter, Not Harder
L. W. Brittian
Mechanical-Electrical Instructor
lwbrittian@hot1.net
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