Electro-magnetic interference (EMI) and leakage currents
Countermeasures against inverter-generated EMI
Some electromagnetic noises enter the inverter to malfunction it, and others are radiated by the in-
verter 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. Al-
so, since the inverter chops outputs at high carrier frequency, that could generate electromagnetic
noises. If these electromagnetic noises cause peripheral devices to malfunction, EMI countermeas-
ures 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
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
– Install data line filters (page 3-8) to signal cables.
– Ground (Earth) the shields of the detector connection and control signal cables with cable
● Techniques to reduce electromagnetic noises that are radiated by the inverter to cause the
peripheral devices to malfunction (EMI countermeasures)
Inverter-generated noises are largely classified into
– those radiated by the cables connected to the inverter and inverter main circuits (I/O),
– those electromagnetically and electrostatically induced to the signal cables of the peripheral
devices close to the main circuit power supply,
– and those transmitted through the power supply cables.
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Precautions for use of the inverter
Noise directly radiated
Noise radiated from
power supply cable
Noise radiated from
motor connection cable
through power supply
Noise from earthing
(grounding) cable due
to leakage current