SMA STP 15000TL Installation - Manual (Page 77)

SMA Solar Technology AG Troubleshooting
Installation Manual STP20TLHE-IA-IEN122222 77
11.2 Checking the Function of the Varistors
If the inverter displays event number "7401", 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 (see Section 8 "Disconnecting the Inverter from Voltage Sources"
(page 58)).
2. Loosen the screws of the upper enclosure lid. For
this purpose, use an Allen key (AF 4).
3. Pull the enclosure lid forwards to remove it.
NOTICE!
Destruction of the inverter due to overvoltage
If varistors are missing or defective, the inverter is no longer protected against overvoltages.
• Replacement varistors should be obtained as soon as possible.
• In PV plants with a high risk of overvoltages, never operate the inverter without
varistors
DANGER!
Danger to life due to high voltages in the inverter
Death due to electric shock
There is residual voltage in the inverter. The inverter takes 20 minutes to discharge.
• Wait 20 minutes before you open the upper enclosure lid or the DC lid.
CAUTION!
Risk of burns due to hot components inside the inverter
• Wait until the components inside the inverter have cooled down.