UPS Circuits with Single Wire

What do you mean by still using the hot wire?

You switched the source to your UPS? How?

Diagram?

Some UPS / Inverters use SPDT relay to change power from mains to battery generated AC and normally remain connected to mains live wire. Even when switch on UPS is switched OFF, the mains live voltage may keep coming at the output. Neutral is taken as common wiring. Such designs have only one wire coming out of the UPS/Inverter.

What do you mean by "a different phase"?

Do you have a polyphase electric supply?

Do you have a polyphase UPS?

It sounds like you may have a code violation here, but you need to clarify your understanding of how the various elements are connected. This will have the incidental benefit of making it possible to ask a question which can actually be answered.

Try drawing a schematic diagram, remembering that an overloaded grounded (neutral) conductor will overheat just like any other overloaded conductor, and a neutral conductor can be used for multiple outlets only if all are on the same branch circuit. There are other rules that have to be followed, too. For example, that the ampacity of conductors must be derated if more than a minimal number are inside a conduit.

If you do this, you may discover that you have answered your own question.

Mains = the MAIN supply to your site.

If you have different phases (like 3 phase supply + Neutral) to your site, then you can use any phase to the UPS. Use a dedicated Phase and Neutral to the UPS, with a circuit breaker just for the UPS to cover its rating.

As long as the circuits connected to your UPS outlet are not connected to any other source of supply (The Hot and Neutral of the UPS must be used. Do not connect the neutral from another source. This will help you not to make any mistakes or mixing neutrals from different branches!), you are OK. Any mix-up will probably Blow your UPS input circuits or the Outout circuits... Dangerous.

Thank you friends! Let me rephrase my situation. I had a house wired with three phase connection, distributing different phases in different rooms. Originally UPS was not installed. All wiring was CONCEALED. When a UPS was installed, existing conduits of CONCEALED wiring could not accommodate two more wires and so only NEUTRAL was wired in, using the positive from the room. Now I imagine the room has a Miniature CB wired in the HOT wire. While UPS has its own MCB, again possibly installed in HOT wire. And the HOT wire belongs to another connection metered separately but from the same Electric POLE (Naturally any one of the three phases). So as it is, There are two circuit breakers, to complete the circuit. My imagination fails me to see why should MCB of UPS fail and not that of the ROOM HOT WIRE, which already carries other loads. I do not know how to make a sketch on this forum. I hope I have drawn a picture in words and certainly not a thousand words.

I think that you are in big trouble!

You should not attempt this trouble shooting yourself!

If you can't make a sketch /drawing of the circuits involved then you can't really understand the solution that you might get in this forum. GET A QUALIFIED ELECTRICIAN. (Capitals for emphasis only).

The MCB of the UPS is tripping because I suspect you wired it such that there is now a short circuit between 2 phases! This is not a healty situation and someone can get hurt badly.(Apart of destroying your UPS etc.)

It sounds like the electrician put your UPS in series with the circuit originally. That's probably ok, the power from the UPS comes from the breaker, through the UPS, and then back into the wall. To do it well, the neutral should also should have been routed through the UPS, so the UPS circuits would be able to monitor the neutral, to protect your appliances from errant electricity gremlins.

To feed this UPS from another leg of the mains would require disconnecting the original hot wire. Now, all the appliances would be powered by the new leg, and the original hot wire would feed nothing.

If the new leg is from a generator or some source not wired to your mains, you will need the neutral from that source, too. If that is the case, make sure you disconnect the old neutral wire from this circuit back to the mains.

If the new circuit is not from the mains, it must stand alone. You may be able to use the old green, ground circuit as long as it goes directly to ground, not through the neutral buss bar.