Mitsubishi Electric FR-A700 Technical Manual page 124

1.6.7 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 flows 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):
1) If possible, use
(grounding) in figure below for the inverter. If
independent earthing (grounding) is not available,
Other
Inverter
equipment
(I) Independent earthing (grounding).......Best
common
(common)
(l) independent earthing
Inverter
(II) Common earthing (grounding).......Good
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
connecting to an iron structure frame, and electric
shock prevention type earthing (grounding) with
the independent earthing (grounding) together.
2) This inverter must be earthed (grounded).
Earthing (grounding) must conform to the
requirements
regulations and electrical code. (NEC section 250,
IEC 536 class 1 and other applicable standards).
3) Use the thickest possible earth (ground) cable.
The earth (ground) cable should be of not less
than the size indicated in the table on the page
530.
4) The grounding point should be as near as
possible to the inverter, and the ground wire
length should be as short as possible.
5) 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
(III) Common earthing (grounding).......Not allowed
117
SPECIFICATIONS
type earthing (grounding)
of national and local safety
Other
equipment
1