Fuji Electric FRENIC-Ace series, User Manual

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11.3 Molded Case Circuit Breaker (MCCB), Residual-current-operated Protective Device
(RCD)/Earth Leakage Circuit Breaker (ELCB) and Magnetic Contactor (MC)
11-8
11.3 Molded Case Circuit Breaker (MCCB), Residual-current-operated
Protective Device (RCD)/Earth Leakage Circuit Breaker (ELCB) and
Magnetic Contactor (MC)
11.3.1 Function overview
■ MCCBs and RCDs/ELCBs* * With overcurrent protection
Molded Case Circuit Breakers (MCCBs) are designed to protect the power circuits between the power supply and
inverter’s main circuit terminals ([L1/R], [L2/S] and [L3/T]) from overload or short-circuit, which in turn prevents
secondary accidents caused by the broken inverter.
Residual-Current-Operated Protective Devices (RCDs)/Earth Leakage Circuit Breakers (ELCBs) function in the
same way as MCCBs.
Built-in overcurrent/overload protective functions protect the inverter itself from failures related to its input/output
lines.
■
Magnetic contactor
An MC can be used at both the power input and output sides of the inverter. At each side, the MC works as
described below. Use it as necessary. When inserted in the output circuit of the inverter, the MC can also switch the
motor drive power supply between the inverter output and commercial power lines.
At the power supply side
Insert an MC in the power supply side of the inverter in order to:
(1) Forcibly cut off the inverter from the power supply (generally, commercial/factory power lines) with the
protective function built into the inverter, or with the external signal input.
(2) Stop the inverter operation in an emergency when the inverter cannot interpret the stop command due to
internal/external circuit failures.
(3) Cut off the inverter from the power supply when the MCCB inserted in the power supply side cannot cut it off
for maintenance or inspection purpose. For the purpose only, it is recommended that you use an MC capable
of turning the MC ON/OFF manually.
Avoid frequent ON/OFF operation of the magnetic contactor (MC) in the input (primary) circuit;
otherwise, the inverter failure may result.
The frequency of the MC’s ON/OFF should not be more than once per 30 minutes. To assure
10-year or longer service life of the inverter, it should not be more than once per hour.
If frequent start/stop of the motor is required, use FWD/REV terminal signals or the
/ keys
on the inverter’s keypad.
At the output side
Insert an MC in the power output side of the inverter in order to:
(1) Prevent externally turned-around current from being applied to the inverter power output terminals ([U], [V],
and [W]) unexpectedly. An MC should be used, for example, when a circuit that switches the motor driving
power supply between the inverter output and commercial power lines is connected to the inverter.
If a magnetic contactor (MC) is inserted in the inverter’s output (secondary) circuit for switching the
motor to a commercial power or for any other purposes, it should be switched on and off when both
the inverter and motor are completely stopped. This prevents the contact point from getting rough
due to a switching arc of the MC. The MC should not be equipped with any main circuit surge killer
(Fuji SZ- ZM□, etc.).
Applying a commercial power to the inverter’s output circuit breaks the inverter. To avoid it,
interlock the MC on the motor’s commercial power line with the one in the inverter output circuit so
that they are not switched ON at the same time.
(2) Drive more than one motor selectively by a single inverter.
(3) Selectively cut off the motor whose thermal overload relay or equivalent devices have been activated.
Driving the motor using commercial power lines
MCs can also be used to switch the power supply of the motor driven by the inverter to a commercial power supply.
Select the MC so as to satisfy the rated currents listed in Table 11.2-1, which are the most critical RMS currents for
using the inverter (Refer to Table 11.3-1). For switching the motor drive source between the inverter output and
commercial power lines, use the MC of class AC3 specified by JIS C8325 in the commercial line side.