We have an Online-UPS connected as per the diagram. The output is given to a change-over switch.

So If we want to feed the computers direct AC we switch it to Source O (Top) for bypass and if we want to give it UPS-Output we switch to Source 1 (bottom on change-over).

If the Change-Over is set to Top (Bypass) the reading at the UPS Input Terminals are as follows

  1. Across Point A and Point B : 230v
  2. Across A and Ground : 230v
  3. Across B and Ground : 0v

Now if the change-over is set to bottom (UPS Output), the voltages are as follows, Note the UPS output is still not switched on.

  1. Across Point A and Point B : 190v
  2. Across A and Ground : 230v
  3. Across B and Ground : 40v

If I turn the UPS output ON, the UPS starts beeping saying Battery Voltage Very Low please turn off UPS.

Is the connection done wrongly?

Edit: Verified ground between terminals and building ground. All seems to be fine. The UPS is getting Ground from the building's ground.

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  • I suspect your UPS is not grounded correctly. How is ground provided to your load (computers)? What is the change-over switch make and model? – RedGrittyBrick Jun 28 '16 at 9:08
  • verified ground connections. Computers are grounded with a wire that is connected to the building's ground terminal. Terminals are showing continuity between ground terminals (Wall Sockets/UPS Ground/Appliance Ground). – user2967920 Jun 28 '16 at 9:31
  • Sounds like you have a bad neutral connection between the UPS and supply. This is also likely stopping it charging, hence the low battery voltage. – SomeoneSomewhereSupportsMonica Jun 28 '16 at 11:41
  • Neutral is bad indeed. Thanks Someone Somewhere. – user2967920 Jun 28 '16 at 12:42

Previous Setup enter image description here

So what was happening here is once the change-over was not set to AC, the common neutral was not linking to the UPS output.

Had the wiring reconfigured in the following way. Things are back to normal. enter image description here

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