ABB ACS 800 Series, Hardware Manual

Page: 41 / 101

41
Planning the Electrical Installation
Protecting the Relay Output Contacts and Attenuating
Disturbances in Case of Inductive Loads
Inductive loads (relays, contactors, motors) cause voltage transients when switched
off.
The relay contacts on the RMIO board are protected with varistors (250 V) against
overvoltage peaks. In spite of this, it is highly recommended to 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 may
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 RMIO board terminal block.
24 VDC
230 VAC
X25
1 RO1
2 RO1
3 RO1
X26
1 RO2
2 RO2
3 RO2
X27
1 RO3
2 RO3
3 RO3
Relay outputs
RMIO
230 VAC
Diode
Varistor
RC filter