Fronius Backup Controller 3PN-35A Automatic Transfer Switch

The Fronius Backup Controller 3PN-35A is an automatic transfer switch (ATS) that enables seamless switchover to full backup mode during grid outages. The controller independently detects power loss and switches the household to emergency operation, then automatically returns to grid-parallel operation once power is restored, ensuring continuous power supply even when occupants are away.

Designed for quick and cost-effective installation, the unit mounts on a standard 35 mm DIN rail within the meter box, eliminating the need for a separate changeover box and reducing installation complexity. It is compatible with Fronius Primo, Symo GEN24 Plus, and Verto Plus inverters (15–20 kW power classes).

The device is rated for 3-phase AC supply at 230/400 V with a maximum current of 35 A, supporting grid types TN-C-S, TN-S, and TT. It includes fault ride-through capability and operates reliably at sea levels up to 2000 m.