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2.5.5
Earthing (grounding) precautions
• Always earth (ground) the motor, the inverter, and the converter unit.
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, 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 distinguished,
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:
• 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 code (NEC
section 250, IEC 61140 class 1 and other applicable standards).
• Use the thickest possible earthing (grounding) cable. The earthing (grounding) cable should be the size indicated in the
table on
page
38.
• 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.
Converter
Inverter
unit
(I) Independent earthing (grounding).......Good
NOTE
• To be compliant with the EU Directive (Low Voltage Directive), refer to
40
2. INSTALLATION AND WIRING
2.5 Main circuit terminals
Other
Converter
equipment
unit
(II) Common earthing (grounding).......Good
Other
Inverter
equipment
(III) Common earthing (grounding) cable.......Not allowed
page
117.
Converter
Other
Inverter
unit
equipment
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