Installation; Installation Guidelines - Siemens SIMATIC 500 Series Description And Operating Instructions

4 Setting Up

4.4 Installation

4.4.1 Installation guideline
Electromagnetic compatibility (EMC)
Electromagnetic compatibility (EMC) covers all aspects regarding the effects of radiated and received electrical,
magnetic, and electromagnetic emissions.
In order to prevent interference in electrical systems, these effects must be reduced to a minimum. The structural
design and correct connection of bus lines as well as the interference suppression of switched inductances play a
major role in limiting interference.
Interference suppression of switched inductances
Shield grid
over lamp
Fig. 6: Interference suppression of fluorescent
lamps in cabinet
Arrangement of devices and cables
Reducing interference by providing adequate space:
A simple yet effective way of reducing interference is to separate devices and cables causing interference from
those affected by interference. Inductive and capacitive interference injection decreases by the square of the
distance between the elements concerned. This means that doubling the distance reduces the interference by
a factor of 4. If the arrangement of the various elements in a building or in the switch cabinet is taken into con-
sideration at the planning stage, the cost of the necessary interference suppression measures is generally very
low.
Please note:
Between an OLM and a power switching element (e.g. contactor, relay, temperature regulator, switch, etc.)
a minimum separation of 15 cm is to be maintained. This minimum separation is to be measured between
the outer edges of the components and in all directions around an OLM.
The power supply wires (+24 V DC and m) for the OLM must not be laid in the same cable duct as cables
for load circuits.
The wires (+24V DC and m) should be twisted together.
Standard recommendations for the arrangement of devices and cables:
EN 50174–2 contains recommendations for arranging devices and cables which are aimed at reducing mutual
interference to a minimum.
20
Shielded cable
Metal-encased
switch
Mains filter or
shielded mains cable
Suppressing switched inductances with fuses:
Switching inductances, e.g. in relays and fans,
generates interference voltages which are many
times higher than the switched operating voltage.
These interference voltages can affect electronic
devices.
The interference voltages of inductances must be
limited at their source of emission by means of
fuses (by connecting diodes or RC elements).
Only use interference suppressors which are
intended for the used relays and fans.
Cabinet lighting:
Use filament lamps (e.g. LINESTRA lamps) for the
cabinet lighting. Do not use fluorescent lamps
because they generate interference fields. If the
use of fluorescent lamps cannot be avoided, the
interference suppression measures shown in
Fig. 6 must be implemented.
4.4 Installation
Version 2.1 10/01