Mitsubishi Electric FR-E700 Series Instruction Manual page 43

Wiring
Notes on earthing
m
CAUTION:
Leakage currents flow in the inverter or the EMC filter respectively. To prevent an electric shock,
the inverter, input filter and motor must be earthed. (This inverter must be earthed. Earthing
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 standards)).
Use the dedicated earth terminal to earth the inverter. (Do not use the screw in the casing, chassis,
etc.)
Use the thickest possible earth cable. Use the cable whose size is equal to or greater than that indi-
cated in Tab. 3-6, and minimize the cable length. The earthing point should be as near as possible to
the inverter.
Always earth the motor and inverter.
● 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.
● 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:
– Where possible, use independent earthing for the inverter. If independent earthing (I) is
impossible, use joint earthing (II) where the inverter is connected with the other equipment
at an earthing point. Joint earthing as in (III) must be avoided as the inverter is connected with
the other equipment by a common earth cable.
Also a leakage current including many high frequency components flows in the earth cables
of the inverter and inverter-driven motor. Therefore, they must use the independent earthing
method and be separated from the earthing 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
with steel frames and carry out electric shock prevention type earthing in the independent
earthing method.
– This inverter must be earthed. Earthing 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 standards).
– Use the thickest possible earth cable. The earth cable should be of not less than the size
indicated in Tab. 3-6.
– The grounding point should be as near as possible to the inverter, and the ground wire length
should be as short as possible.
– 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.
Inverter
(I) Independent earthing
Fig. 3-4:
FR-E700SC EC
Other
equipment
(best solution)
Earthing the drive
Inverter Other
equipment
(II) Common earthing
(good solution)
Main circuit connection
Inverter Other
equipment
(III) Common earthing
(not allowed)
I001016E
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