Mitsubishi Electric FR-F720P-0.75K to 110K Instruction Manual page 33

Main circuit terminal specifications
(2) Notes on earthing (grounding)
Always earth (ground) the motor and inverter.
1)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
flow into the case. The purpose of earthing (grounding) 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 (grounding) is important to audio equipment, sensors,
computers and other apparatuses that handle low-level signals or operate very fast.
2)Earthing (grounding) methods and earthing (grounding) work
As described previously, earthing (grounding) 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 (grounding):
(a) If possible, use (l) independent earthing (grounding) in figure below for the inverter. If independent earthing
(grounding) is not available, use (ll) joint earthing (grounding) in the figure below which the inverter is
connected with the other equipment at an earthing (grounding) point.
The (lll) common earthing (grounding) as in the figure below, which inverter shares a common earth
(ground) cable with the other equipment, must be avoided.
A leakage current including many high frequency components flows in the earth (ground) cables of the
inverter and inverter-driven motor. Therefore, use the independent earthing (grounding) and separated the
earthing (grounding) cable of the inverter from equipments sensitive to EMI.
In a high building, it may be effective to use the EMI prevention type earthing (grounding) connecting to an
iron structure frame, and electric shock prevention type earthing (grounding) with the independent earthing
(grounding) together.
(b) This inverter must be earthed (grounded). Earthing (Grounding) must conform to the requirements of
national and local safety regulations and electrical code (NEC section 250, IEC 536 class 1 and other
applicable standards).
A neutral-point earthed (grounded power supply for 400V class inverter in compliance with EN standard
must be used.
(c) Use the thickest possible earth (ground) cable. The earth (ground) cable should be of not less than the size
indicated in the above table on the previous page.
(d) The earthing (grounding) point should be as near as possible to the inverter, and the earthing (grounding)
wire length should be as short as possible.
(e) Run the earth (ground) 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 EU Directive (Low Voltage Directive), refer to the Instruction Manual (Basic).
22
Other
Inverter
equipment
(II) Joint earthing.......Good
Other
Inverter
equipment
(III) Joint earthing.......Not allowed