Mitsubishi A2USCPU(S1), User Manual

Page: 149 / 272

9 - 4
EMC AND LOW VOLTAGE DIRECTIVES 9.
9.1.3 Cables
The cables pulled out of the control panel contain a high frequency noise component. On
the outside of the control panel, therefore, they serve as antennas to emit noise. Ensure to
use shielded cables for the cables, which are connected to the I/O modules, special
function modules and those pulled out to outside of the control panel.
Mounting ferrite core is not required except some types of CPU however, noise emanated
via the cable can be restrained using it.
The use of a shielded cable also increases noise resistance. The signal lines (including
common line) connected to the programmable controller I/O modules and special function
modules use shielded cables to assure noise resistance, as a condition, standardized on
EN61131-2/A12(2000). If a shielded cable is not used or not earthed correctly, the noise
resistance will be less than the specified value.
(1) Earthing of shielded cables
(a) Earth the shield of the shielded cable as near the control panel as possible
taking care so that the earthed cables are not induced electromagnetically by the
cable to be earthed.
(b) Take appropriate measures so that the shield section of the shielded cable from
which the outer sheath cover was partly removed for exposure is earthed to the
control panel on an increased contact surface. A clamp may also be used as
shown in the figure below. In this case, however, apply a cover to the painted
inner wall surface of the control panel which comes in contact with the clamp.
Note) The method of earthing by soldering a wire onto the shield section of the
shielded cable as shown below is not recommended. The high
frequency impedance will increase and the shield will be ineffective.