38 Planning the electrical installation
Protecting the contacts of relay outputs and attenuating
inductive loads
Inductive loads (relays, contactors, motors) cause voltage transients when switched
off.
Equip inductive loads with noise attenuating circuits (varistors, RC filters [AC] or
diodes [DC]) in order to minimize the EMC emission at switch-off. If not suppressed,
the disturbances might connect capacitively or inductively to other conductors in the
control cable and form a risk of malfunction in other parts of the system.
Install the protective component as close to the inductive load as possible. Do not
install protective components at the I/O terminal block.
1) Relay outputs; 2) Varistor; 3) RC filter; 4) diode
24 V DC
0 V DC
230 V AC
230 V AC
1
2
3
4
0 V DC
24 V DC
4
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