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

Describe the funtion and operation of:

DC fused disconnect switches

• Used for small motors and control circuitry
• The disconnect is for isolation purposes only, does not provide automatic protective features
• The fuses provide overcurrent protection for the load and circuit

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Function and operation of:

DC MCC disconnect switch

• Provides positive isolation of load from source
• Interlocked to prevent opening door when in ON position

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Function and operation of:

DC MCC Molded Circuit Protector

• Adjustable magnetic trip device
• Auto trips on fault (excessive current)
• Reset by taking handle to OFF then ON

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Function and operation of:

DC MCC Current limiter

• Provides interruption capacity above range handled by MCP
• Built-in trip indicators for each phase
• Requires replacement after interrupting faults

Function and operation of:

DC MCC Fuses

• Fuses are primary means of overcurrent protection for load and control circuit
• Load fuses are installed on both positive and negative terminals
• Control circuitry has its own set of fuses

Function and operation of:

DC MCC thermal overload device

• Consists of a heater element that will open a contact in control circuit to stop motor
• Can be reset with pushbutton on door, once cooled
• May provide an alarm vs a trip, on some systems

Function and operation of:

DC MCC control relays

• Energized by control circuit logic
• Energizing a starter control relay sends power to starter device
• The starter control relay and additional relays operate contacts in the control circuit logic

Function and operation of:

DC MCC Starter

• Magnetic contact device that will connect power to the load
• Contained within an arc shield
• Current passing through coil builds up a magnetic field which draws moving contacts towards stationary contacts

Function and operation of:

DC MCC Starting Resistors

• Limit current flow during motor starts, no CEMF exists until motor starts turning
• Dropped out once CEMF is built up

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Wires must be disconnected and tagged when removing a DC MCC