SMA SB 2500TL-21 Installation - Manual (Page 78)

Troubleshooting SMA Solar Technology AG
78 SB25-30TLST-21-IA-en-13 Installation Manual
11.6 Checking the Function of the Varistors
If the inverter displays the event number "7401", 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.
Check the varistors as described below:
1. Disconnect the inverter and open it (see Section 8.2 "Disconnecting the Inverter from Voltage
Sources" (page 57)).
2. Undo the screws of the upper enclosure lid. Use an
Allen key (AF 4) to do this.
NOTICE!
Destruction of the inverter due to overvoltage
If varistors are missing or defective, the inverter is no longer protected against overvoltages.
• In PV plants with a high risk of overvoltages, never operate the inverter without
varistors.
• Replacement varistors should be fitted as soon as possible.
DANGER!
Danger to life due to high voltages in the inverter
The capacitors in the inverter may be charged with very high voltages.
• Wait five minutes before opening the upper enclosure lid, in order to allow time for
the capacitors to discharge.