Update 2022-07-04: I read up quite a bit on pure sine wave UPSs and bought one and so far so good. The whole problem may not have been about grounding but about the garbage sine wave produced by non-sine wave UPSs. I have another compute running on non-sine UPSs so I'll try to report back comparing that computer to the sine wave computer.

Update 2022-05-21: The main problem I was trying to address here was random 'ups dop outs' even under low wattage usage by the pc causing the pc to reboot. As I understand it, some pc power supplies might not like artificial sine wave UPS power: So, my next test will be with a true sine wave UPS. Will update when I've run with one for a while.

Is there any way to use a UPS properly when there's no ground wire in the outlet?

I have a GFCI setup and an outlet with a ground wire but it's not a real ground (apparently; I don't quite understand GFCI). My UPS's that have a 'wiring fault' light indicate a wiring fault (lit up).

My UPS's will sometimes give out (and my computers will reboot), even on low wattage load (like less than 50%), and I suspect it's due to not having proper ground. But they give out even when there's no apparent surge/brown out, no thunderstorm, etc. Should that be happening? Would this not happen if the outlet were properly grounded in a modern way?


  • 1
    Can you trace where the "ground" from the receptacle/outlet in question goes to? Aug 29, 2020 at 19:33
  • As I understand the receptacle ground just isn't hooked up at all.
    – Shovas
    May 21, 2022 at 23:45
  • Can you post photos of the inside of the receptacle box please? May 22, 2022 at 5:24
  • Not sure why the down vote , reversed.
    – Ed Beal
    Jul 4, 2022 at 17:37
  • Do they hold a charge on the battery? I know some UPS models perform self tests and switch over to battery mode. APC's self test is every 2 weeks. If the frequency at which it occurs matches the frequency of the self test of your model, that might be more than a coincidence.
    – rtaft
    Jul 5, 2022 at 20:02

2 Answers 2


While a UPS, and many surge protectors as well, will show wiring faults equivalent to a magic 8-ball, a UPS should never actually use ground, except if there is a true fault. A brownout or blackout should trigger the USP battery/inverter but not actually put any current on the ground wire. In fact, if it did then it would immediately trip the GFCI (assuming that some of that current should have been going on neutral).

More likely is a faulty UPS. The most common fault, unless it is brand new, is a battery that no longer holds a charge properly. UPS detects fault, switches to battery/inverter and promptly fails. Most small UPS now have user-replaceable batteries, though whether that makes sense or not depends on the age of the UPS (other parts can fail over time) and whether it might be time to upgrade to a larger UPS for other reasons.

  • Thanks for answering. The one UPS is quite new and only runs at 50% wattage load, while another UPS I have often runs close to max wattage (but not all the time), and the weird thing is they both exhibit the same symptom: It's like they just randomly give up for no apparent reason and drop out causing the computers to reboot.
    – Shovas
    Aug 30, 2020 at 16:55

The ground is only needed for suppressing line voltage spikes.

Many ups run on their battery power or they convert the line voltage to the battery voltage and then the inverter produces the output voltage.

This sounds wasteful but it prevents and difference in the output waveform when a power bump happens because it was already running on the inverter.

The ground is not really needed with the exception that there are protective devices that clamp the incoming line voltage to a maximum voltage so the electronics powering the battery circuit are not damaged with a spike.

It is true that many switching power supplies (just about every power supply today) do not work well unless the ups is true sine or the wave shaping electronics mimic a sinusoidal waveform closely, this goes into how switching supplies vary the speed or pulse width that is used to charge capacitors to the proper level for the supply output but that is getting a bit beyond diy to fully explain.

  • Thanks for the helpful comment. I've since purchased a pure sine wave UPS and so far so good. I'll post an update later after more time has passed comparing a computer with non-sine UPS with the sine UPS computer.
    – Shovas
    Jul 4, 2022 at 17:20

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