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76 SB20_25_30HF-IEN102911 Installation Guide
11.2 Checking the Functioning of the Varistors
If the inverter displays the event number "74", then one of the varistors is probably defective.
Varistors are wear parts. Their functional efficiency diminishes with age or following repeated
responses as a result of overvoltages It is therefore possible that one of the thermally monitored
varistors has lost its protective function.
You can check the functionality of the varistors in the following manner:
1. Disconnect the inverter on the AC and DC sides as described in section 8”Disconnect the
Inverter from Voltage Sources” (page60).
2. Loosen the screws of the enclosure lid.
3. Remove the enclosure lid.
Position of Varistors
You can determine the position of the varistors using the illustration below.
The varistors are bent upon delivery.
Observe the following assignment of the
terminals.
• Terminal A: outer terminal (varistor
connection with loop [crimp]).
• Terminal B: middle terminal.
• Terminal C: outer terminal (varistor
connection without loop [crimp]).
DANGER!
Danger to life due to high voltages in the inverter.
The capacitors require 5 minutes to discharge.
• Wait 5 minutes before opening the housing cover, in order to allow time for the
capacitors to discharge.
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