A new UPS shuts down after a day of operation. What could be the problem?

Question

Uninterruptable power source

We bought an EXApower UPS for 1800 W with an SNMP card. Load 510 W. He worked for a day and does not turn on anymore. They took it under warranty, brought it back. There are no indications on the screen, not on the squeaker.
They put him to work, asked what happened to him. They said that they replaced the power cable that goes to the UPS, they replaced it, like, it was faulty, although it was checked when it was removed from the UPS. There is 220V on it, there are no kinks.

Turned on, and after 5 minutes, and he died again. Just switched off.
Sent back to service.
They brought us a new one and installed it. Already nothing foreshadowed trouble, well, as it were, a new one.
They set it up again from 9 in the morning, and the next day at 14:20 it went out again and does not turn on anymore. The service was called. They said that we did not connect it correctly.

What could be the problem?

Answer 1

For example, in the parameters of the supply voltage that enters the upsnik. Maybe it's too low / high, maybe there is interference from the welder behind the next wall ...