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How to power two floors with one inverter?

  1. Aug 19, 2012 #1
    Hi,

    I have two floors with two different energy meters. Both energy meters are supplied electricity from different phases of a 3-phase single neutral electric source. The basic schematic is shown in the attached picture.
    xVA1t.jpg

    On floor 1, all load is connected through the inverter.

    On floor 2, some load is direct while some load through inverter. The load through inverter uses live from 1st floor and neutral from 2nd floor.

    Is this okay?
    Will it cause the energy meter to show leakage?

    Thanks engineers :)
     
  2. jcsd
  3. Aug 19, 2012 #2

    NascentOxygen

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    Hi GingerLee. http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif [Broken]

    What does the inverter do, exactly?
     
    Last edited by a moderator: May 6, 2017
  4. Aug 19, 2012 #3

    sophiecentaur

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    If the red lines are live and the black ones neutral then there is no connection from the right hand load to the meter 2. Therefore, you wouldn't expect the meter to register anything.
    Is the inverter / battery a UPS?
     
  5. Aug 19, 2012 #4
    It is a inverter + battery. It is a UPS, used for power backup. In case power fails from main source, the inverter generates AC current from DC battery. When there is no power failure, it just connects load directly to the mains.

    Yes, it is a UPS. and yes red is live and black is neutral.

    What I wanted to know, is it okay to use the neutral from one energy meter and live from another energy meter (through the UPS). Note that both energy meters are fed from different phases.

    In case of no power failure.
    load (shown on lower right) is fed from neutral from energy meter#1(EM1), and live from energy meter#2 (EM2). Is this okay? Will this cause EM2 to show leakage because current from EM1 would go through neutral of EM2?

    I am worried if this would result in a short circuit, over voltage or increased energy bill (due to leakage reading, yes my energy meter also records leakage).

    Thanks again for taking time to respond :)
     
  6. Aug 19, 2012 #5

    sophiecentaur

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    Put a meter between the two neutrals to check but there should be no volts if they are directly off the same three phase transformer (as in the UK and Europe). If you find more than a few mV then you may have to think again. The acid test would be to see if and how the neutral-neutral Volts vary when you switch different loads onto the two phases. (And how the Joule Meter responds, too.
    Good luck
     
  7. Aug 19, 2012 #6

    dlgoff

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    If phases from your transformer secondary are Wye connected with the neutral as shown here:

    http://www.federalpacific.com/university/T-Basics/Charts/section-3-scan-9.gif [Broken]

    there should be no problem sharing this neutral with the power meters. But if you're not sure if the neutrals are coming from the same transformer, do the test as sophiecentaur suggest.
     
    Last edited by a moderator: May 6, 2017
  8. Aug 20, 2012 #7
    Thanks everyone for the replies. I put a digital multi-meter (700V AC) between the two neutral, the voltage was 2-3 volts (it kept changing between 2 and 3). I guess i have to remove the load from the UPS for second floor.

    I dont want buy a new UPS for second floor. This would be costly :(

    Thanks guys :)
     
  9. Aug 20, 2012 #8

    sophiecentaur

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    If you touch the two neutrals together. Do you get a spark? Will your DMM show more than a few mA when connected between the two neutrals.? If no then no worries.
     
  10. Aug 20, 2012 #9

    berkeman

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    Do you pay the energy bill for both meters?
     
  11. Aug 20, 2012 #10

    sophiecentaur

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    Good man! HaHa

    But why not run a second (neutral) line, along with the red one and disconnect load 2 from the other supply completely?
     
  12. Aug 21, 2012 #11
    Yes indeed. This place had two meters when I first came here and I let it be like this. The previous owner used to rent the floors to different people. And they quarreled over who uses more electricity so the owner had 2 meters installed.

    I called the electricity company helpline to remove 1 meter and they said they would charge me for it. Why pay for removing something?

    Great idea. I looked into it but I think I have to call a professional for this. Wiring is inside walls and I don't want to mess with it.

    Actually the guy who installed UPS did install a wire for UPS running from 1st to 2nd floor. He just took 1 white wire (for live coming from UPS) and used the neutral coming from meter. I did not know then or I would have had him install extra neutral too.

    Forgot to do this. I touched the neutrals , they do not create spark. DMM is not stable, it shows between 0 A to 0.010 A. The current stays 0 but when I switch something on (like ceiling fan), then it goes up for a second, then slowly comes back to 0.

    Thanks :)
     
    Last edited: Aug 21, 2012
  13. Aug 22, 2012 #12

    sophiecentaur

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    That worries me. The practice of 'borrowed neutral' is a poor one and I would question this guy's credentials. You would not be likely to find this happen in the UK, for instance. I should have expected a twin and earth cable (three conductors in a separate sleeve).
     
  14. Aug 22, 2012 #13
    I don't see any protection in this circuit I would expect any RCCDs installed upstream of the meters to trip all the time.
     
  15. Aug 23, 2012 #14
    I have RCCD, MCB and Isolator. Just did not show in the circuit to make it simple as it was not relevant to the question I was asking.

    He was sent by the place I bought UPS from. Thanks for the mention of borrowed neutral, I am going to have all wiring checked for this.
     
  16. Aug 23, 2012 #15

    NascentOxygen

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    I, too, had observed that these circuits can't be protected by RCDs. You have just the two meters, and there is an RCCD associated with each of these meters?
     
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