I bought a house in the summer and it came with a sump pump connected via a heavy duty extension cord to a 1000 watt power inverter. The inverter was connected to a battery and the battery connected to an automatic charger.

Last week I found that the fuse (connected between the positive battery terminal and the inverter) had blown. Without thinking too much, I turned the inverter off and unplugged the charger, and started to replace the fuse. As soon as I had screwed the plastic assembly together, the inverter popped and fried itself.

I didn't unplug the extension cord from the inverter going to the sump pump. The pump is also fried (now if I plugin the pump into regular house power, the breaker on the circuit immediately trips).

So...

I don't understand why the inverter blew up. There's only an on/off switch, and it was turned off. It wasn't grounded, unless the ground from the charger to the battery was supposed to take care of that. Could the inverter have been bad already (causing the fuse to blow), or am I missing something obvious?

If enough power went down the extension cord to damage the sump pump's motor, should I assume the extension cord itself is also likely damaged and replace it?

I am having a new pump put in on Friday, but I don't want to redo the battery/inverter setup like the guy had before me. Since the pump is regular household power, am I safe to run it from a UPS - like I use on my computer?

Thanks for the help!

Follow-Up:

The fuse I was replacing in the inverter was an F80A, and I was replacing it with the same (they come in a 4 pack - apparently for use in a care stereo setup). I'm not sure if 80 AMPS on a 1000 Watt inverter was a good match, but it worked all summer without a problem.

The plumber didn't think there was anything wrong with the extension cord, so we re-used it and does seem okay.

A desktop computer UPS isn't suitable for use with a sump pump - The volt amps required to start the motor are typically too high and if the UPS doesn't burn out, the run time is extremely short. A larger class UPS would work, but it's much too expensive to be practical. The battery/inverter model seems to be the most efficient and economical way to go.

I'd appreciate any other input anyone might have!