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1.6.4 Notes on earthing (grounding)
z Use the dedicated earth (ground) terminal to earth (ground) the inverter. (Do not use the screw in the case,
chassis, etc.)
Use a tinned crimping terminal which does not contain zinc to connect the earth (ground) cable. Tighten the
screw, taking care not to break its threads.
z Use the largest possible gauge for the earth (ground) cable. The gauge should be equal to or larger than those
indicated in the following table. The earthing (grounding) point should be as near as possible to the inverter to
minimize the earth (ground) cable length.
(Unit: mm
2
)
For use as a Low Voltage Directive-compliant product, use the PVC cables indicated in the parentheses for earthing
(grounding).
z Earth (Ground) the motor on the inverter side using one wire of the 4-core cable.
z 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
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 (grounding) method.
(b) Earthing (Grounding) must conform to the requirements of national and local safety regulations and
electrical codes.
(NEC section 250, IEC 536 class 1 and other applicable standards).
(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.
(d) The earthing (grounding) point should be as near as possible to the inverter to minimize the earth (ground)
cable length.
(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.
(f) Use one wire in a 4-core cable with the earth (ground) terminal of the motor and earth (ground) it on the
inverter side.
Motor Capacity
Earth (Ground) Cable Gauge
200V 400V
2.2kW or less 2 (2.5) 2 (2.5)
3.7kW 3.5 (4) 2 (2.5)
5.5kW, 7.5kW 5.5 (6) 3.5 (4)
11kW, 15kW 14 (16) 8 (10)
18.5kW to 37kW 22 (25) 14 (16)
45kW, 55kW 38 (35) 22 (25)
(I) Independent earthing (grounding) ... Best
(II) Joint
earthing (grounding)
... Good
(III) Joint earthing (grounding) ... Not allowed
Inverter
Other
equipment
200V class
class D earthing (grounding)
400V class
class C earthing (grounding)
Inverter
Other
equipment
200V class
class D earthing (grounding)
400V class
class C earthing (grounding)
Inverter
Other
equipment
200V class
class D earthing (grounding)
400V class
class C earthing (grounding)