Mitsubishi Electric 800 Series, Instruction Manual, Page: 70 / 727

Electro-magnetic interference (EMI) and leakage currents
PRECAUTIONS FOR USE OF THE INVERTER
69
3
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 70 ) to signal cables.
- Ground (Earth) the shields of the detector connection and control signal cables with cable clamp metal.
• 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.
Noise propagated through
power supply cable
Path (c)
Path (b)
Path (a)
Noise directly
radiated from inverter
Path (d), (e)
Air propagated
noise
Path (f)
Electrical path
propagated noise
Path (h)
Path (g)
Inverter generated
electromagnetic
noise
Electromagnetic
induction noise
Electrostatic
induction noise
Noise radiated from
power supply cable
Noise radiated from
motor connection cable
Noise from earthing
(grounding) cable due to
leakage current
Instrument Receiver
M
Sensor
power supply
Motor
Telephone
Sensor
(a)
(b)
(c)
(c)
(f)
(g)
(e)
(g)
(d)
(f)
Inverter
(a)