piesangbrood

Hi everyone, first time posting here. I'll try and keep it concise. Problem: My UPS often trips the DB board earth leakage instantly when grid power resumes (loadshedding ends). Resetting the earth leakage trips it again 50% of the time, but after the second or third try it succeeds, and the UPS goes from battery to grid, starts to charge the battery, while keeping everything connected to it online. Factors that significantly increase the frequency of trips: When a multi plug with surge protection is connected to the UPS output When the alarm power supply (transformer-based) is connected to the UPS output (almost guaranteed to cause a trip) Without these devices connected to the UPS, the frequency of trips goes from 98% of the time, to maybe once a month. This is still a problem, as with no grid power caused by a trip and no-one home to reset it, eventually the battery will be depleted and eat itself in the process. With the UPS not connected to the grid, the earth leakage never trips. By elimination then, I blame the UPS. Specifications of the UPS: Tescom SSPro long-run 1100VA 12V UPS, connected to an external 105Ah Enertec deep-cycle lead-acid battery UPS input is plugged directly into the wall, on a standard plug circuit All circuits in the house seems to be protected by the earth leakage On the UPS output, only light electronics are connected - TV, soundbar, computer screen (never drawing more than 120W - measured using watt-meter and accounting for power factor). There is nothing fancy with this setup - no special wiring, no separate DB board, nothing. Think of a standard APC / RCT UPS that you use for a computer, plugged into a standard socket, powering your PC. This is like that, only with a larger external battery (the UPS is designed for this), and with a socket that supports three-prong plugs. I tested one other UPS (APC 1000VA SmartUPS) and one inverter (Homaya 850VA) with all the above connected, including the alarm power system, and they did not ever cause a trip. All these UPSs / inverter are pure sine wave, although that shouldn't be a factor. Something peculiar I noticed - with the UPS running from battery, and input power socket removed, I can feel a slight buzz on the plug prongs across live / neutral (maybe earth too, cannot remember). Not enough to shock me, but there's some 50hz backfeed there which I'm pretty sure is the cause of the issue. My cheap multimeter cannot give me a reading, unfortunately. The other APC UPS and inverter does not do this at all. I guess it tries to "sense" the AC waveform of the grid, so that when grid power resumes, the UPS can switch connected devices over to the grid with, the AC waveform in sync. I've been recommended to connect the UPS to a separate house plug circuit which bypasses the earth leakage (as the UPS apparently has protections of its own on the output side), but this feels like avoiding the source of the issue at best, and unsafe at worst. For all I know, maybe it tries to sync when the inverted power is at a peak, and grid power is at a trough, effectively causing a "short" when the two are connected? I would appreciate the community's thoughts on this. I am not a professional in electronics, so my apologies in advance for incorrect interpretations. However, I'm always happy to learn.