Mitsubishi Electric FR-F740-00023-EC Instruction Manual page 21

Main circuit terminal specifications
(2) Notes on earthing
Always earth the motor and inverter.
1)Purpose of earthing
Generally, an electrical apparatus has an earth 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
flow into the case. The purpose of earthing the case of an electrical apparatus is to prevent operator from
getting an electric shock from this leakage current when touching it.
To avoid the influence of external noises, this earthing is important to audio equipment, sensors, computers and
other apparatuses that handle low-level signals or operate very fast.
2)Earthing methods and earthing work
As described previously, earthing is roughly classified into an electrical shock prevention type and a noise-
affected malfunction prevention type. Therefore, these two types should be discriminated clearly, and the
following work must be done to prevent the leakage current having the inverter's high frequency components
from entering the malfunction prevention type earthing:
(a) Where possible, use independent earthing for the inverter. If independent earthing (I) is impossible, use
joint earthing (II) where the inverter is connected with the other equipment at an earthing point. Joint
earthing as in (III) must be avoided as the inverter is connected with the other equipment by a common
earth cable.
Also a leakage current including many high frequency components flows in the earth cables of the inverter
and inverter-driven motor. Therefore, they must use the independent earthing method and be separated
from the earthing of equipment sensitive to the aforementioned noises.
In a tall building, it will be a good policy to use the noise malfunction prevention type earthing with steel
frames and carry out electric shock prevention type earthing in the independent earthing method.
(b) This inverter must be earthed. Earthing must conform to the requirements of national and local safety
regulations and electrical codes. (JIS, NEC section 250, IEC 536 class 1 and other applicable standards).
(c) Use the thickest possible earth cable. The earth cable should be of not less than the size indicated in the
above table on the previous page.
(d) The grounding point should be as near as possible to the inverter, and the ground wire length should be as
short as possible.
(e) Run the earth cable as far away as possible from the I/O wiring of equipment sensitive to noises and run
them in parallel in the minimum distance.
Other
Inverter
equipment
(I)Independent earthing.......Best
To be compliant with the European Directive (Low Voltage Directive), refer to the Instruction Manual (basics).
10
Other
Inverter
equipment
(II)Common earthing.......Good
Other
Inverter
equipment
(III)Common earthing.......Not allowed