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Precautions for Peripheral Device Selection
Selection and installation of molded case
circuit breaker
Install a molded case circuit breaker (MCCB) on the power receiving
side to protect the wiring of the inverter input side. For MCCB
selection, refer to page 30 since it depends on the inverter power
supply side power factor (which changes depending on the power
supply voltage, output frequency and load). Especially for a
completely electromagnetic MCCB, one of a slightly large capacity
must be selected since its operation characteristic varies with
harmonic currents. (Check the manual of the corresponding
breaker.) As an earth leakage circuit breaker, use the Mitsubishi
earth leakage circuit breaker designed for harmonics and surge
suppression. (Refer to page 31)
When installing a molded case circuit breaker on the inverter output
side, contact the manufacturer of each product for selection.
Handling of the input side magnetic contactor
• For operations using external terminals (using terminal STF or
STR), install the input-side magnetic contactor to prevent
accidents due to automatic restart when the power is restored
after power failures such as an instantaneous power failure, or for
safety during maintenance works. Do not use this magnetic
contactor for frequent starting/stopping of the inverter. (The
switching life of the converter part is about 500,000 times.) In the
operation by parameter unit, the automatic restart after power
restoration is not performed and the magnetic contactor cannot
be used to start the motor. The input-side magnetic contactor can
stop the motor. However, the regenerative brake of the inverter
does not operate, and the motor coasts to a stop.
Handling of the output side magnetic contactor
Switch the magnetic contactor between the inverter and motor only
when both the inverter and motor are at a stop. When the magnetic
contactor is turned on while the inverter is operating, overcurrent
protection of the inverter will activate. For instances in which an MC
is provided to switch to a commercial power supply, first turn off the
inverter and motor, then switch the MC.
Installation of thermal relay
The inverter has an electronic thermal O/L relay to protect the motor
from overheating. However, install an external thermal overcurrent
relay (OCR) between the inverter and motors to operate several
motors or a multi-pole motor with one inverter. In this case, set 0 A to
the electronic thermal O/L relay setting of the inverter. For the
external thermal overcurrent relay, determine the setting value in
consideration of the current indicated on the motor's rating plate and
the line-to-line leakage current. (Refer to page 34.)
For low-speed operation where the cooling capability of the motor
reduces, it is recommended to use a thermal relay protector
incorporated motor.
Output side measuring instrument
When the inverter-to-motor wiring length is long, especially for the
400 V class, small-capacity models, the meters and CTs may
generate heat due to line-to-line leakage current. Therefore, choose
the equipment which has enough allowance for the current rating.
Disuse of power factor improving capacitor
(power factor correction capacitor)
Do not add a capacitor or surge suppressor to the inverter.
This is because the power factor improving capacitor and surge
suppressor on the inverter output side may be overheated or
damaged by the harmonic components of the inverter output.
Furthermore, the inverter already has inbuilt protection against
excessive current flow. To improve the power factor, use a reactor.
Electrical corrosion of the bearing
• When a motor is driven by the inverter, axial voltage is generated
on the motor shaft, which may cause electrical corrosion of the
bearing in rare cases depending on the wiring, load, operating
conditions of the motor or specific inverter settings (high carrier
frequency, use of a capacitive filter
Contact your sales representative to take appropriate
countermeasures for the motor.
The following shows examples of countermeasures for the
inverter.
• Decrease the carrier frequency.
• Remove the capacitive filter.
• Provide a common mode choke
inverter. (This is effective regardless of the use of the
capacitive filter.)
∗1
Mitsubishi Electric capacitive filter: FR-BIF, SF[], FR-E5NF-[], FR-
S5NFSA[]
∗2
Recommended common mode choke: FT-3KM F series
®
FINEMET
common mode choke cores manufactured by Hitachi
Metals, Ltd.
FINEMET is a registered trademark of Hitachi Metals, Ltd.
Cable gauge and wiring distance
If the wiring distance is long between the inverter and motor, during
the output of a low frequency in particular, use a large
cable gauge for the main circuit cable to suppress the voltage drop
to 2% or less. (The table on page 30 indicates a selection example
for the wiring length of 20 m.)
Especially for long-distance wiring or wiring with shielded cables, the
inverter may be affected by a charging current caused by stray
capacitances of the wiring, leading to an incorrect activation of the
overcurrent protective function. Refer to the maximum wiring length
shown in the following table. When multiple motors are connected,
use the total wiring length shown in the table or shorter.
Cable type
012
022
036
050
Unshielded
50m 50m 50m 50m 50m 100m 100m 100m 100m
Shielded
25m 25m 50m 50m 50m 100m 100m 100m 100m
Model FR-CS82S-[]
Cable type
025
042
070
100
Unshielded
50m 50m 50m 50m
Shielded
25m 25m 50m 50m
When driving a 400 V class motor by the inverter, surge voltages
attributable to the wiring constants may occur at the motor terminals,
deteriorating the insulation of the motor. In this case, use a 400 V
class inverter-driven insulation-enhanced motor.
When the wiring length is 50 m or more, set "8" (8 kHz) or less in
Pr.72 PWM frequency selection.
Use the recommended connection cable when connecting the
parameter unit.
For remote operation using analog signals, keep the distance
between the remote speed setter and the inverter to 30 m or less.
Also, to prevent induction from other devices, keep the wiring away
from the power circuits (main circuit and relay sequential circuit).
When setting the frequency using a external potentiometer rather
than a parameter unit, use a shielded or twisted cable as shown in
the figure below. Connect the shield cable to terminal 5, not to the
earth (ground).
(3)
10
(2)
2
(1)
5
Frequency setting
Twisted
potentiometer
cable
).
∗1
on the output side of the
∗2
Model FR-CS84-[]
080
120
160
230
295
Shielded cable
(3)
10
(2)
2
(1)
5
Frequency setting
potentiometer
11
33
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