Can UPS Work Properly on an Ungrounded (2-Wire) Circuit?

[Anonymous user]

I would like to buy and use a UPS to protect the PC and LCD monitor in my home-office, but the electrical wiring in my old home is not grounded (it's a 2-wire circuit and an AC-ground tester indicates that my outlets are not grounded)!

I've been told that a properly grounded electrical circuit is required for a UPS to detect the power-drop and take-over in a timely manner. I would appreciate knowledgeable feedback as to whether or not a UPS (such as the APC BE750G) will work properly in my home environment.

[Anonymous user · Accepted solution]

Ok, but even if the surge-suppression doesn't work, will the UPS still function properly if I experience a power-outage?

[TheNotoriousKMP_apc]

Yes.

[Anonymous user]

Well, that's better than no power-protection at all ...isn't it?

Thanks.

[TheNotoriousKMP_apc]

Because of the wiring, the Site Wiring Fault LED will be illuminated at all times on the UPS.

That's the indication of a missing ground.

And during any type of electrical problem, surge, etc. the UPS will not be able to shunt the excessive voltage to the ground (as it's non-existant), and will ultimately damage your equipment. The Equipment Protection Policy will not be upheld due to the wiring.


I can tell you I recently lived in an apartment with a missing ground (they just installed a 3-prong outlet and left the grounding wire leading to nowhere), which triggered a SWF on my UPS. I was VERY uneasy using it during an electrical storm and powered it down numerous times.

[Anonymous user]

The surge Protection might still work to some extent since there are MOVs (the main surge protection component) put between Phase (hot) - Neutral. The neutral wiring is grounded at the same point the safety ground is conected. The difference is that there is current running on the neutral wiring all the time and on the safety ground wiring, there isnt. Small surges caused by other appliences are diverted to neutral, so against this your UPS is still offering surge protection, but against lightning strike, this is not very likely without the safety ground.

Depending on the lightning strike, even with a grounded outlet, there is no garantee of full protection. Agains very near lightning strikes or direct strikes, there should be a whole house surge protector installed, a good one point ground system, all metalic lines coming in your house should be protected as well since lightning surges can come in from telephone lines, cable TV, satellite dishes, antenas...