Troubleshooting; Troubleshooting For Circuit-Breaker Proper (Mccb/Elcb) - Mitsubishi Electric C Series Handling And Maintenance

Moulded case circuit breakers, earth leakage circuit breakers, earth leakage relays & circuit protectors

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5. Troubleshooting

5.1 Troubleshooting for circuit-breaker proper (MCCB/ELCB)

Trouble

Foreign matter in switching mechanism

Closing impossible

No resetting

Resetting impossible

Wear due to trip endurance

Poor reset mechanism

(*) Resetting impossible

Non-excitation of undervoltage coil

Tripping impossible

Resetting time has not elapsed

OFF impossible

Breakage and/or fatigue of the

switching spring

Fusion of contact due to excessive interruptive current

Excessive operation power

Poor positional relationship between the external handle and the

circuit-breaker

Excessive shock from exterior

Insulating material mingled between contacts

Corrosion by infiltrating rain water, etc.

Fused conductive portion

Large consumption of contact

Breakage of rated changeover screw

Excessive tightening torque (tighten with 3 to 4.5 kg-cm of torque)

Too high an ambient temperature

Too high a temperature rise

Troublesome operation

Deviation of applied frequency (thermal-

under normal load

adjustable electromagnetic type 800AF or higher)

Load current strained with much high component

Rather small measurements by error of measuring instrument due to distorted current

Too small a setting of rated current

Electronic

Overcurrent

Tightening forgotten of the changeover screw of rated current

type

display

Failure of rated current changeover portion

MCCB

LED is on

Exothermic reaction due to repeated starting current

Erroneous action while

starting

Too long a starting time

Too high a starting current

Too high a starting rush current

Transient current when changing delta connection to star one. Transient current due to reversible operation

Instantaneous action

Rush current at the time of instantaneous restart

during starting

Rare short-circuit of motor

Bimetal reset incomplete after instantaneous tripping

Abnormal current running simultaneously with closing (short-circuit closing)

Transmission was made with antenna of transceiver (5W or higher)

Operating while in use

closely mounted on the electronic MCCB and earth leakage breaker

Shift from the short-circuit of another conductor

Short-circuit on line side

Accumulated dust

Fall of conductor on line side

Poor tightening

Too high a temperature on

Contact heavily consumed

the terminal side

Increased contact resistance

Complete electromagnetic type used in high frequency (400 Hz, for instance)

Too high a temperature on

Load current distorted containing much high frequency component

the lateral side of the

Erroneous measurement dependent on feeling

mould

Loosened stud

Exothermic reaction of the

Poor contact between the conductive portion of stud and the body terminal

tightened portion of stud

Groove machining forgotten for reduction of eddy-current exothermic reaction of rear-connected type iron mount plate (400AF or higher)

Too high a rated current selected

No tripping with over

Wrong frequency applied

current

Tripping of backup circuit-breaker

Overcurrent display LED does

not come on. Or, though it

The battery of breaker tester has come at the end of its service life.

comes on, it goes off sonner

than normal.

Overcurrent display LED comes

Poor tripping mechanism

on and goes off after prescribed

time. But, no tripping.

Cause

See below (*)

Incessant use of voltage trip operation

End of service life

Poor adjustment

Carelessness

Breakage by initial trouble

End of service life

Excessive interrupting current

Short-circuit current cut off. End of service life

Application of overcurrent

Erroneous selection (temperature correction)

Board hermetically closed

Loosened connection to terminal

Erroneous selection (frequency)

Erroneous selection

Poor maintenance

End of service life

Intrusion of rust and dust

Too low a current for instanta-

neous tripping of backup breaker

Countermeasure

Foreign matters to be removed

To be reset once again

See below

To be replaced with new one, Voltage trip to be replaced by electric operation

To be replaced with new one

To be returned for repairing

To be excited

Wait until the bimetal is cooled down

To be returned for repairing

To be replaced by new one

To be replaced by circuit-breaker with large breaking capacity

Handle to be replaced

Revision of positional relationship

To be replaced with new one

Foreign matter to be removed (with removable cover)

To be returned for repairing (with unremovable cover)

To be replaced with new one

To be replaced by new one with larger breaking capacity

To be replaced with new one

To be returned for repairing

Rating selection to be changed

Ventilation

Retighten

To be replaced with circuit-breaker of suitable frequency

Distortion factor to be decreased by reactor

To be measured correctly by a meter with true effective value, and correct selection of rating

Correct the setting of rated current

Correct retightening of the rated current changeover screw with tightening torque: 3 to 4.5 kg-cm

To be returned for repairing

To be replaced by a unit with higher rating

Electromagnetic setting to be change or the unit to be replaced by one with higher rating

Motor to be repaired

To be fully restored

Circuit to be checked to remove the cause

Transceiver to be used at a distance at least 1 m from the electronic

MCCB

Cause to be removed To be replaced with new one

Retighten

To be replaced by new one

Foreign matters to be removed

Suitable frequency to be selected To be changed into thermal type.

Distortion factor to be decreased by reactor Selection of rating to be changed

To be measured with a measuring instrument

Retighten

Reassemble the stud

Groove to be provided

To be replaced by a unit with lower rating

Suitable frequency to be selected

Instantaneous electromagnetic switch to be lowered

Raise the electromagnetic setting of backup breaker or change the rating

Battery to be replaced.

To be returned for repairing.

Selection of rating to be changed

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