Mitsubishi Electric FR-F720-00046 Instruction Manual page 32

(2) Notes on grounding
Always ground the motor and inverter.
1)Purpose of grounding
Generally, an electrical apparatus has an 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 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 grounding is important to audio equipment, sensors, computers
and other apparatuses that handle low-level signals or operate very fast.
2)Grounding methods and grounding work
As described previously, 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 grounding:
(a) If possible, use (l) independent grounding in figure below for the inverter. If independent grounding is not
available, use (ll) joint grounding in the figure below which the inverter is connected with the other
equipment at a grounding point.
The (lll) common grounding as in the figure below, which inverter shares a common ground cable with the
other equipment, must be avoided.
A leakage current including many high frequency components flows in the ground cables of the inverter
and inverter-driven motor. Therefore, use the independent grounding and separated the grounding cable of
the inverter from equipments sensitive to EMI.
In a high building, it may be effective to use the EMI prevention type grounding connecting to an iron
structure frame, and electric shock prevention type grounding with the independent grounding together.
(b) This inverter must be grounded. 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 grounded power supply for 400V class inverter in compliance with EN standard must be
used.
(c) Use the thickest possible ground cable. The ground 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 grounding wire length should be
as short as possible.
(e) Run the 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 Installation Guideline.
Other
Inverter
equipment
(II) Joint earthing.......Good
Main circuit terminal specifications
Other
Inverter
equipment
(III) Joint earthing.......Not allowed
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