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) If possible, use (l) independent earthing in figure below for the inverter. If independent earthing is not
available, use (ll) joint earthing in the figure below which the inverter is connected with the other equipment
at an earthing point.
The (lll) common earthing as in the figure below, which inverter shares a common earth cable with the
other equipment, must be avoided.
A leakage current including many high frequency components flows in the earth cables of the inverter and
inverter-driven motor. Therefore, use the independent earthing and separated the earthing cable of the
inverter from equipments sensitive to EMI.
In a high building, it may be effective to use the EMI prevention type earthing connecting to an iron
structure frame, and electric shock prevention type earthing with the independent earthing together.
(b) This inverter must be earthed. Earthing 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 power supply for 400V class inverter in compliance with EN standard must be
(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 earthing point should be as near as possible to the inverter, and the earthing 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.
(I) Independent earthing.......Best
To be compliant with the EU Directive (Low Voltage Directive), refer to the Installation Guideline.
(II) Joint earthing.......Good
(III) Joint earthing.......Not allowed