Main Circuit Terminal Specifications - Mitsubishi Electric FR-D720-008 Instruction Manual

Main circuit terminal specifications

The line voltage drop can be calculated by the following formula:
3 × wire resistance[mΩ/m] × wiring distance[m] × current[A]
line voltage drop [V]=
Use a larger diameter cable when the wiring distance is long or when it is desired to decrease the voltage drop (torque
reduction) in the low speed range.
(2) Earthing (Grounding) precautions
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, 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)This inverter must be earthed (grounded). 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).
Use an neutral-point earthed (grounded) power supply for 400V class inverter in compliance with EN standard.
(c)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 previous page 17.
(d)The earthing (grounding) point should be as near as possible to the inverter, and the earth (ground) cable 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.
Inverter
(I)Independent earthing.......Best
POINT
To be compliant with the European Directive (Low Voltage Directive),
18
1000
Other
Inverter
equipment
(II)Common earthing.......Good
Other
Inverter
equipment
(III)Common earthing.......Not allowed
refer to the Installation Guideline.
Other
equipment