Notes on grounding
Leakage currents flow in the inverter. To prevent an electric shock, the inverter and motor must be grounded.
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 standards)
Use the dedicated ground terminal to ground the inverter. (Do not use the screw in the case, chassis, etc.)
Use the largest possible gauge for the ground cable. The gauge should be equal to or larger than those indicated
in the following table. The grounding point should be as near as possible to the inverter to minimize the ground
3.7kW (5HP) or less
22kW, 37kW (30HP, 50HP)
Ground the motor on the inverter side using one wire of the 4-core cable.
Always ground the motor and inverter.
(1)Purpose of grounding
Generally, an electrical apparatus has an 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 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 grounding is important to audio equipment, sensors, computers
and other apparatuses that handle low-level signals or operate very fast.
(2)Grounding methods and grounding work
As described previously, 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 grounding:
(a) Where possible, use independent grounding for the inverter.
If independent grounding (I) is impossible, use joint grounding (II) where the inverter is connected with the
other equipment at an grounding point. Joint grounding as in (III) must be avoided as the inverter is
connected with the other equipment by a common ground cable.
Also a leakage current including many high frequency components flows in the ground cables of the
inverter and inverter-driven motor. Therefore, they must use the independent grounding method and be
separated from the 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 grounding with steel
frames and carry out electric shock prevention type grounding in the independent grounding method.
(b) This inverter must be grounded. 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 standards).
(c) Use the thickest possible ground cable. The ground cable should be of not less than the size indicated in
the above table.
(d) The grounding point should be as near as possible to the inverter to minimize the ground cable length.
(e) Run the 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 ground terminal of the motor and ground it on the inverter side.
(I) Independent grounding ... Best
Ground Cable Gauge
(II) Joint grounding ... Good
(III) Joint grounding ... Not allowed