Planning the electrical installation 71
Protecting the contacts of relay outputs
Inductive loads (relays, contactors, motors) cause voltage transients when switched
off. The voltage transients can connect capacitively or inductively to other conductors
and cause a malfunction in the system. To protect the contacts of relay outputs,
• Use a noise attenuating circuit (varistors, RC filters [AC] or diodes [DC]) which
minimizes the EMC emission of inductive loads at switch-off.
• Install the noise attenuating circuit as close as possible to the inductive load.
• Do not install a noise attenuating circuit at the relay output.
230 V AC
+ 24 V DC
230 V AC
Diode
RC filter
Varistor
Relay outputs
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