Mitsubishi Electric 800 Series Installation Manualline page 28

WIRING
2.3.3 Earthing (grounding) precautions
Always earth (ground) the motor and inverter.
Purpose of earthing (grounding)
Generally, an electrical apparatus has an earth (ground) terminal, which must be connected to the ground before use.
An electrical circuit is usually insulated by an insulating material and encased. However, it is impossible to manufacture an
insulating material that can shut off a leakage current completely, and actually, a slight current flows into the case. The
purpose of earthing (grounding) the case of an electrical apparatus is to prevent operators from getting an electric shock
from this leakage current when touching it.
To avoid the influence of external noises, the earthing (grounding) is important to EMI-sensitive equipment that handle
low-level signals or operate very fast such as audio equipment, sensors, and computers.
Earthing (grounding) system to be established
As described previously, the purpose of earthing (grounding) is roughly classified into the electrical shock prevention and
the prevention of malfunction due to the influence of electromagnetic noise. These two purposes should be clearly distin-
guished, and the appropriate earth (ground) system must be established to prevent the leakage current having the
inverter's high frequency components from reversing through another earth (ground) point for malfunction prevention by
following these instructions:
l Make the separate earth (ground) connection (I) for high frequency products such as the inverter from any other devices
(EMI-sensitive devices described above) wherever possible.
Establishing adequate common (single-point) earth (ground) system (II) shown in the following figure is allowed only in
cases where the separate earth (ground) system (I) is not feasible. Do not make inadequate common (single-point)
earth (ground) connection (III).
As leakage currents containing many high frequency components flows into the earthing (grounding) cables of the
inverter and peripheral devices (including a motor), the inverter must also be earthed (grounded) separately from EMI-
sensitive devices described above.
In a high building, it may be effective to use its iron structure frames as earthing (grounding) electrode for EMI
prevention in order to separate from the earth (ground) system for electric shock prevention.
– Earthing (Grounding) must conform to the requirements of national and local safety regulations and electrical codes
(NEC section 250, IEC 61140 class 1 and other applicable standards). A neutral-point earthed (grounded) power
supply for 400 V class inverter in compliance with EN standard must be used.
– Use the thickest possible earthing (grounding) cable. The earthing (grounding) cable should be the size indicated in
the table on page 17.
– The earthing (grounding) point should be as close as possible to the inverter, and the earth (ground) wire length
should be as short as possible.
– Run the earthing (grounding) cable as far away as possible from the I/O wiring of the EMI-sensitive devices and run
them in parallel in the minimum distance.
Other
Inverter
equipment
(I) Separate earthing (grounding): Good
CAUTION
l To be compliant with the EU Directive (Low Voltage Directive), refer to the document enclosed with the product.
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Other
Inverter
equipment
(II) Common (single-point) earthing (grounding): OK
Other
Inverter
equipment
(III) Inadequate common (single-point) earthing (grounding): Bad