Homage new ups fuse blown issue

Hi, I just got installed a new homage inverter. After charging the batteries I turned on the ups supply by cutting the Wapda supply from the main breaker, which caused dc fuse to blown away. I had the professional technician to install it. Batteries were connected in series as per specification and house wiring is also in good condition (now running the load on same ups wire).

I am using new Vertex2414 with 2 Osaka batteries. What could be the reason for it.?

If DC polarity is correctly wired, then,
In-rush current, due to charging of DC-bus capacitors. maybe.

Is UPS a/c power output connection to house wiring single wire (phase only) or two wires and (phase+neutral)?