Protecting The Contacts Of Relay Outputs - ABB PVS800-57B Hardware Manual

Planning the electrical installation 43

Protecting the contacts of relay outputs

Inductive loads (relays, contactors and motors) cause voltage transients when switched
off.
When you connect inductive loads to the customer I/O, equip the loads with noise
attenuating circuits (varistors, RC filters [AC] or diodes [DC]) to minimize the EMC
emissions at switch-off. If they are not suppressed, the disturbances can connect
capacitively or inductively to the other conductors in the control cable and cause a
malfunction.
Install the protective component as close to the inductive load as possible. Do not install
protective components at the relay outputs.
1
230 V AC
2
230 V AC
3
+24 V DC
4
-
1) Relay outputs, 2) varistor, 3) RC filter, 4) diode