SMA AUTOMATIC SWITCH BOX M-20 - Manual (Page 50)

8 Maintenance and Cleaning SMA Solar Technology AG
50 AS-BOX-M_L-IA-IEN110320 Installation Guide
8 Maintenance and Cleaning
The Automatic Switch Box must be maintained and, if necessary, cleaned at regular intervals. SMA
Solar Technology AG recommends to carry out particular maintenance work every 12 months. Note
that the maintenance interval is influenced by the installation site and the ambient conditions.
If the Automatic Switch Box is used in a TN system, the operational grounding resistance needs to be
checked every 5 years.
Maintaining the Automatic Switch Box
• Check interior of the Automatic Switch Box for dirt, moisture and water penetration.
– If necessary, clean the Automatic Switch Box and take appropriate actions.
• Check all connections to ensure that they are securely in place.
– If necessary, re-connect the cables to the connection terminals.
• Check cable insulations, connection terminals and thermal fuses for discoloration.
– If external cabling (e.g. cables leading to loads, PV plant, generator etc.) is discolored,
exchange the cables.
– If interior cabling (e.g. cables leading to contactors or thermal fuses) is discolored, contact
the SMA Serviceline.
Checking the operational grounding resistance
1. Disconnect the Automatic Switch Box from voltage sources (see section 7).
2. Measure the resistance value between the connection terminals "N" of the terminal strips
"AS-X2/ SBU 5000" and "GND (PE)" of the terminal strip "AS-X8" with a test equipment having
an overvoltage category of at least 3.
☑ The resistance is between 225 ohm and 275 ohm.
✖ The resistance is smaller than 225 ohm or larger than 275 ohm?
The N-PE resistance is defective.
• Contact the SMA Serviceline.