1. Rapidly disconnect fault from system
2. Minimize system disruption
3. Keep system component damage to a minimum

• Magnetic Molded Case Breakers
• Trip when sufficient current passes through an electromagnet.
• Usually set at 10 to 13 times full load current.
• Trip free position, requires operator reset.
• Thermal-Magnetic Molded Case Breakers
• Bi-metallic strip heats up and releases latch
• Thermal overcurrent set at 125% full load current
• Instantaneous overcurrent protection from electromagnet

From tripped/neutral position, take toggle switch to OFF then to ON

Function and Operation of MCC Bucket:

Control Power Transformer

• Provides single phase 120VAC to control, auxiliary and indication circuits.

Function and operation of MCC Bucket:

Contactors

Contactors contain electromagnetic relays that close the contacts in the main power supply to the load when they are energized by the control circuit

Function and operation of MCC Bucket:

Thermal Overloads

• Provide overcurrent protection for each phase of a motor
• Any one phase actuation will cause an open in the control circuit
• Can be reset when cooled

• Eutectic (solder pots) - Reset by pushbutton on MCC door - does NOT require opening door. Eutectic devices are bring phased out and replaced with bi-metallic devices.

• Bi-metallic (dissimilar metals) - Pushbutton does not align with button on MCC door; therefore, door must be opened to reset.

Function and operation of MCC Bucket:

Terminal Blocks

• Terminal blocks provide connection points for contol, auxiliary and indication circuits

Function and operation of MCC Bucket:

Seismic Clips

• Provide rigid support for MCC bucket housing
• Safeguard buckets have 4 clips
• Non-safeguard buckets have 2 clips

Function and operation of 480V Load Center Breaker:

Closing Springs

• Discharged to close the breaker
• Charged by an AC motor, or manually when control power is unavailable

Function and operation of 480V Load Center Breaker:

Arc Chutes

• Contain metal arc barriers to elongate and cool the arc from the arcing contacts

Function and operation of 480V Load Center Breaker:

Trip Buttons

• Mechanical trip button opens breaker manually

Function and operation of 480V Load Center Breaker:

Automatic Trip Indicator

• Protrudes from front plate to indicate an overcurrent trip, can be reset by pushing back in

Function and operation of 480V Load Center Breaker:

Automatic Trip Lockout

• Mechanically prevents closing breaker after an overcurrent trip
• Can be reset by pushing in automatic trip indicator

Function and operation of 480V Load Center Breaker:

Padlocking device

• Provides a means for locking the breaker in the trip free position
• Maintains manual trip button in trip direction (inwards) when locking plate is held forward
• Push manual trip inward to push locking plate outward

Function and operation of 480V Load Center Breaker:

Closing Spring Charge Indicator

• Indicates whether spring is charged or discharged,
• Closing spring is automatically charged after tripping (closing) unless motor disconnect switch is in OFF

Function and operation of 480V Load Center Breaker:

Motor disconnect switch

• Toggle switch connected in series with charging motor,
• Used to disconnect motor from voltage source

Function and operation of 480V Load Center Breaker:

Electrical Close Pushbutton

• Used to electrically close breaker from the front panel,
• If breaker can be operated remotely this can only be performed in the TEST position

Function and operation of 480V Load Center Breaker:

Manual Close Lever

• Provides a means of manually closing the breaker without control power

Function and operation of 480V Load Center Breaker:

Racking Mechanism

• Used to move the circuit breaker to CONNECTED, TEST, or DISCONNECTED positions,
• Racking shutter interlocked with breaker contacts
• Contacts must be open for shutter to lift
• Breaker cannot be closed when shutter open

Function and operation of 480V Load Center Breaker:

Emergency Charging Device

A maintenance handle is used to charge the closing springs, the breaker can be closed manually once the springs are charged

• CONNECTED
• Main breaker connections are connected
• All control contacts are connected
• TEST
• Main breaker connections are disengaged from bus
• Certain control contacts are connected to allow testing breaker operation
• DISCONNECTED
• Main breaker connections are disengaged from bus
• All control contacts are disengaged

Identify the function and operation of 2.3/4.16/13.2 KV breaker:

Arcing contacts

• Set of moving and stationary contacts that make connection before the main contacts
• Arcing contacts are replaceable, burning and pitting from arcing is normal for breaker operation

Identify the function and operation of 2.3/4.16/13.2 KV breaker:

• Consist of a set of moving and stationary contacts that supply power from the bus to the load when closed

Identify the function and operation of 2.3/4.16/13.2 KV breaker:

• Cylindrical operated bellows, with a nozzle, that provide a blast of air to force the arc (generated during breaker opening) into the arc chute

Identify the function and operation of 2.3/4.16/13.2 KV breaker:

Ceramic enclosures that use plates to elongate and cool generated arcs

Identify the function and operation of 2.3/4.16/13.2 KV breaker:

Act as insulators for each phase by surrounding the arc chutes

Identify the function and operation of 2.3/4.16/13.2 KV breaker:

Identify the function and operation of 2.3/4.16/13.2 KV breaker:

• A spring that forces the main and arcing contacts to close and charge the opening spring,
• Closing spring is charged by a DC motor at the end of a closing cycle or when the breaker is racked-in to the TEST position (aux contacts madeup in test)

Identify the function and operation of 2.3/4.16/13.2 KV breaker:

• Charged by a ratcheting mechanism connected to a DC motor,
• Charged after breaker is closed, or
• When breaker is racked-in to TEST

Identify the function and operation of 2.3/4.16/13.2 KV breaker:

Breaker opening is accomplished by energizing a solenoid (trip coil) that will release the energy stored in the opening spring, to force the main and arcing contacts open.

Solenoid can be opened manually/mechanically with the trip pushbutton.

Identify the function and operation of 2.3/4.16/13.2 KV breaker:

• Used to change breaker position (connected/test/disc) within the housing
• The release lever must be rotated to the left to turn the racking mechanism
• The release lever cannot be moved to the left when the breaker main contacts are closed, to prevent racking in or out a CLOSED breaker

Identify the function and operation of 2.3/4.16/13.2 KV breaker:

Primary/Secondary disconnects

Primary disconnects - 6 disconnects used to connect the breaker to the line and bus terminals. They are connected to the bus and line when the breaker is in the CONNECTED position.

Secondary disconnect - Single (1) contact that connects control power to the breaker when in TEST or CONNECTED positions.

Identify the function and operation of 2.3/4.16/13.2 KV breaker:

Auxiliary Switches

Identify the function and operation of 2.3/4.16/13.2 KV breaker:

Safety shutter

Automatically covers the bus and line ports when the breaker is removed from the compartment, to provide worker protection.

Identify the function and operation of 2.3/4.16/13.2 KV breaker:

Ground bus contacts and motor extension

Ground bus contacts engage a ground bus extension to provide ground protection for the breaker.

Contacts are located in the bottom rear of the breaker.

Extension is located between the floor guides toward the front of the housing.

Provide protection of equipment and workers by connecting electrical systems or components to ground,

Provide safe access to live terminals for bus/line phase-out testing,

Capable of connecting either the BUS or LINE side to ground

Function and operation of ground truck:

Selector switch

Determines whether the BUS or LINE side will be connected to ground

Operated using a removable handle on the left side of the ground truck

Visual verification of selector switch position can be made at the rear of the ground truck and a position indicator is available on the front of the truck

Function and operation of ground truck:

Main contacts

Function and operation of ground truck:

Ground truck control station

• Connected to ground truck control cable,
• Controls closing of ground truck main contacts 

Function and operation of ground truck:

Test Ports

Allow access to terminals for checking/comparing voltages on the BUS and LINE

Function and operation of ground truck:

Key interlock system