How to Maintain Auxiliary Circuits

Functions

Auxiliary circuits are made of two parts, an electrical or mechanical accessory with the associated wiring:

• Voltage releases (XF, MX, MN)

• Gear motor (MCH)

• Indication contacts (OF, CE, CT, CD, SDE, PF)

Auxiliary wiring links devices and transmits the following information:

• Orders to the control devices

• Status-condition information

Voltage Releases

The voltage releases (XF, MX, MN) can be standard or with communicating function (XF, MX).

The XF closing voltage release closes the circuit breaker instantaneously when powered if the spring mechanism is charged.

The MX opening voltage release opens the circuit breaker instantaneously when powered.

The MN undervoltage release instantaneously opens the circuit breaker when its supply voltage drops to a value between 35% and 70% of its rated voltage.

It is important to periodically check operation of the voltage releases at minimum values. Whether the auxiliary needs to be replaced depends on the operating conditions and environmental conditions. It is recommended that you replace voltage releases every 15 years.

MCH Gear Motor

The MCH gear motor automatically recharges the operating mechanism springs as soon as the circuit breaker is closed.

The MCH gear motor makes it possible to close the device immediately after opening. The spring charging handle serves as a backup if the auxiliary voltage is interrupted.

Given the mechanical forces exerted to charge the mechanism, periodic checks on the operation of the MCH gear motor and the charging time are required to help ensure the device closing function.

Indication Contacts

Contacts indicate the following information:

• OF: position of the main contacts (opened or closed)

• CE, CT, CD: position of the device in the chassis (connected, test, or disconnected)

• SDE: trip due to an electrical fault

• PF: the device is ready to close

This information enables a remote operator to respond as necessary. Incorrect indications can result in erroneous device operation.

Improper contact performance can be caused by vibrations, corrosion, or abnormal temperature rises. Preventive maintenance consists in regularly checking that contacts conduct or isolate correctly, depending on their position.

Auxiliary Wiring

Auxiliary wiring is used to transmit the following information:

• Orders to the various control devices

• Status-condition information

Incorrect connections or damaged insulation can cause unintended opening or non-operation of the circuit breaker. The auxiliary wiring must be regularly inspected and replaced as required, particularly in environments with vibrations, high ambient temperatures, or corrosive atmosphere.

Degradation Factors

The factors which can cause degradation of the auxiliaries are the following:

• High ambient temperature

• Humidity

• Corrosive atmosphere

• Vibration

Potential Hazards

Performing regular maintenance on the auxiliaries can help to avoid the potential hazards and consequences listed in the following table.

Preventive Action

The following table lists the preventive maintenance procedures to be performed to maintain the control unit.

For more information, refer to Preventive Maintenance Programs.