Service and maintenance
10.2 Troubleshooting
3VL IEC molded case circuit breakers
System Manual, 11/2013, 110 0110 - 02 DS 03
127
Troubleshooting
Notes on troubleshooting
Table 10- 1 Troubleshooting
Overload causes
circuit breaker to trip:
Excessive current
The circuit breaker is functioning correctly and switches off an overload
that occurs. Check to see if the operating current has exceeded the
Connecting cable not
correctly connected to the
circuit breaker
Carry out a visual inspection of the terminals for discoloration. Cables
can become loose during service due to various reasons such as
vibration (machine tool applications) and cold flow (for aluminum
Ambient temperature too
high
This can be a problem on hot summer days or in areas subject to
extreme heat. Although all 3VL molded case circuit breakers are
calibrated for use at an ambient temperature of 50 °C, the
temperatures in the enclosures can exceed this level. It may be
necessary to consider derating the I
n
or I
R
values. See the Chapters
Use in unusual environments, and Derating factors
Overcurrent release not
correctly connected to the
circuit breaker.
If none of the above suggestions apply, the overcurrent release must
be removed from the molded case circuit breaker and inspected for
discoloration. The tightening torque values are listed in the operating
manual supplied with every circuit breaker.
Short-circuit causes
circuit breaker to trip:
Excessive making
current, e.g. motor
Adjust the magnetic trip rating to the next highest setting or until the
circuit breaker does not trip when the motor is started.
High current peaks, e.g.
when changing from star
to delta in star-delta
A current peak of up to 20 times the rated current of the motor can
occur when changing from star to delta. In this case, the short-circuit
release "I" must be set to a higher value. However, this may result in
the loss of the desired higher motor protection function.
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