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
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) Where possible, use independent earthing (grounding) for the inverter. If independent earthing (grounding) (I)
is impossible, use joint earthing (grounding) (II) where the inverter is connected with the other equipment at an
earthing (grounding) point. Joint earthing (grounding) as in (III) must be avoided as the inverter is connected
with the other equipment by a common earth (ground) cable.
Also a leakage current including many high frequency components flows in the earth (ground) cables of the
inverter and inverter-driven motor. Therefore, they must use the independent earthing (grounding) method and
be separated from the earthing (grounding) 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 (grounding) with
steel frames and carry out electric shock prevention type earthing (grounding) in the independent earthing
(b) This inverter must be earthed (grounded). Earthing (Grounding) 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
(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 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 (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.
(III)Common earthing.......Not allowed