Analysis Of Unnecessary Operation; Classification Of Elcb Operation; Detail Of Operation - Mitsubishi Electric C Series Handling And Maintenance

5.4 Analysis of unnecessary operation

Operation of ELCB by the causes on purpose, leak current, electrification, ground fault etc., is normal,
while operation by other causes such as surge and induction is unnecessary (called stray operation or
nuisance trip). It seems that quite a number of users have the preconception that earth leakage circuit
breakers are troublesome as they operate unreasonably. Therefore, unnecessary operation is analyzed
and selection of correct ELCB is stated in the following text.

5.4.1 Classification of ELCB operation

ELCB operation is classified as follows;
Normal
operation
Operation
Unnecessary
operation

5.4.2 Detail of operation

(1) Normal operation
Operation of ELCB according to each purpose. Primary examples are shown below.
1 Deterioration of equipment insulation ...... This is often the case with water handling devices such
2 Deterioration of wire insulation ................ This is often the case with joints and terminals of tempo-
3 Faulty work .............................................. Ground fault by damage or disconnection of cables dur-
4 Careless handling .................................... Electrification by wetting and ground fault by surge or
(2) Fault of ELCB
Failure caused by deterioration and corrosion of parts but fault of the leak detecting unit is rare. In
some cases, closing becomes unstable because of wear of the magnet or the switching mechanism.
Besides such fault, ELCB of low balancing characteristic tends to operation when the motor starts. It
is, therefore, necessary, to use ELCB made by reliable manufacturers.
(3) Inadequate sensitivity current
ELCB operates if the sensitivity current is too sensitive compared with normal leak current of the
circuit. This is a matter of selection.
In most cases, leak current from circuits is attributable to static capacity to ground of the wire. Of some
electric furnaces and sheath heaters, the insulation resistance comes down when cooled even if the
insulation resistance is enough at high temperature, and it takes time to find out the cause of ELCB
operation.
As to leak current from circuits, it must also be noted that ELCB is operated not only by leak current
under normal condition but also by transient leak current to ground at switching or at start-up. Transient
leakage at start-up is generated through static capacity to the frame of winding as potential distribution
of winding at start-up differs from that during operation.
81
(1) Operation by leak current, electrification, ground
fault etc.
Those
(2) Fault of earth leakage circuit breaker
attributable
(3) Inadequate sensitivity current (too sensitive)
to ELCB
(4) Operation by surge
(5) Operation by circulation current
(6) Operation by induction
(7) Operation by wrong wire connection
(8) Operation by inadequate earth
(9) Operation by influence of at ground fault of shunt
Those
circuit
attributable
to circuit and
(10) Operation by overload or short-circuit
others
(11) Operation by environment (vibration, impact etc.)
(12) Operation by carrier phone unit
(13) Operation by electromagnetic wave
(14) Operation by inverters
(15) Others (Operation of surge absorber etc.)
as washing machine and those subjected to high impact
such as press machine.
rarily installed electric lines.
ing work.
dropped foreign matter.