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3. PRECAUTIONS FOR USE OF THE INVERTER
3.1 Electro-magnetic interference (EMI) and leakage currents
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Countermeasures
• Use Pr.9 Electronic thermal O/L relay.
• If the carrier frequency setting is high, decrease the Pr.72 PWM frequency selection setting.
Note that motor noise increases. Selecting Pr.240 Soft-PWM operation selection makes the sound inoffensive.
To ensure that the motor is protected against line-to-line leakage currents, it is recommended to use a temperature sensor to
directly detect motor temperature.
Installation and selection of the molded case circuit breaker
Install a molded case circuit breaker (MCCB) on the power receiving side to protect the wiring at the inverter input side. Select
an MCCB according to the inverter input side power factor, which depends on the power supply voltage, output frequency and
load. Especially for a completely electromagnetic MCCB, a slightly large capacity must be selected since its operation
characteristic varies with harmonic currents. (Check it in the data of the corresponding breaker.)
3.1.2 Countermeasures against inverter-generated EMI
Some electromagnetic noises enter the inverter to cause the inverter malfunction, and others are radiated by the inverter to
cause the peripheral devices to malfunction. Though the inverter is designed to have high immunity performance, it handles
low-level signals, so it requires the following basic techniques. Also, since the inverter chops outputs at high carrier frequency,
that could generate electromagnetic noises. If these electromagnetic noises cause peripheral devices to malfunction, EMI
countermeasures should be taken to suppress noises. These techniques differ slightly depending on EMI paths.
Basic techniques
• Do not run the power cables (I/O cables) and signal cables of the inverter in parallel with each other and do not bundle
them.
• Use shielded twisted pair cables for the detector connecting and control signal cables and connect the sheathes of the
shielded cables to terminal SD.
• Ground (Earth) the inverter, motor, etc. at one point.
Techniques to reduce electromagnetic noises that enter and cause a
malfunction of the inverter (EMI countermeasures)
When devices that generate many electromagnetic noises (which use magnetic contactors, electromagnetic brakes, many
relays, for example) are installed near the inverter and the inverter may malfunction due to electromagnetic noises, the
following countermeasures must be taken:
• Provide surge suppressors for devices that generate many electromagnetic noises to suppress electromagnetic noises.
• Install data line filters (page 74) to signal cables.
• Ground (Earth) the shields of the detector connection and control signal cables with cable clamp metal.
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