live amps & neutral amps

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solarking
solarking Registered Users Posts: 67 ✭✭
in Solar Beginners Corner #1
why there are neutral and live amps reading on electric meters? what is the real purpose of neutral amps
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #2
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    The north American 120/240 60Hz residential feed is split phase (180 degrees apart) between the two hot leads.

    Simple way is that it is a center tapped transformer feeding the home.

    You cannot measure the current in just one leg. The neutral leg current is the sum of the A and B hot leg currents. Remember that A and B are 180 degrees out of phase. So 10 amps on A, 0 amps on equals 10 amps on neutral.

    10 amps on A and 10 amps on B equals 0 amps on the neutral.

    So, our electric meter needs to measure current on two legs of the three wire circuit.

    And remember 10 amps × 120 volts = 1,200 Watts. And 10 amps × 240 volts = 2,400 Watts.

    So the meter needs both voltage and current to figure out the billing.

    As to 120 vs 240 vac, probably because the first power systems were DC and Edison's filament light was designed for 110 vac. The first A.C. systems were designed to support the 110 VDC bulbs and appliances.

    Tesla wanted 220/240 VAC but, by this time, major appliances like refrigerators and such were already in wide use in the US and expensive to replace. In Europe, not so much at the time.

    Also 110 volts is much lures likely to injure or kill vs 220 volts. The danger of electricity was a big issue back in the days of Edison and Tesla.

    - Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Lumisol
    Lumisol Registered Users Posts: 374 ✭✭✭
    #3
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    He also wanted to have his free distribution of power without wires to be set up all over the us. If that had been done, there would be no off-grid anymore. The air is the grid.
    But since Morgan couldn't meter it, it was shot down and buried.
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  • mvas
    mvas Registered Users Posts: 395 ✭✭✭
    edited June 2017 #4
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    The amps in the Neutral Wire is always equal to the difference between the amps measured in Hot Line #1 and Hot Line #2.



    If all of your loads were 240 Volts ( ie 240 Volt Water Heater ) then the neutral wire is "technically" not needed ...
    Line #1 @ 10 Amps - Line #2 @ 10 Amps =  Neutral Wire @ 0 Amps.

    However, when you have unequal 110 Volt loads (very likely) then the neutral wire must carry the difference ...
    Line #1 @ 10 Amps - Line #2 @ 5 Amps = Neutral Wire @ 5 Amps
    Line #1 @ 10 Amps - Line #2 @ 0 Amps = Neutral Wire @ 10 Amps

    Things get more complicated if you have a GTI and one leg is consuming power and one leg is providing power to the grid.
    "Smart" Utility Meters can detect this, but most humans using a typical DVM cannot.
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  • solarking
    solarking Registered Users Posts: 67 ✭✭
    #5
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    What happens when neutral line is only fed to the input of the inverter and only the phase from the inverter output and neutral from the input  is supplied to the load.
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  • mvas
    mvas Registered Users Posts: 395 ✭✭✭
    edited June 2017 #6
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    solarking said:
    What happens when neutral line is only fed to the input of the inverter and only the phase from the inverter output and neutral from the input  is supplied to the load.
    Are you describing ... a 120 Volt Grid-Tie Inverter connection?

    The GTI will reduce the loading on that half of the 240 V AC transformer and the Power Meter will slow down appropriately.
    I do not believe that my Residential Meter actually measures the amps flowing through the Neutral.
    I am billed for the SUM of  ...
    Line #1 Watts = Amps through Line #1 x 120 V AC 
    Line #2 Watts = Amps through Line #2 x 120 V AC 
    ===========
        Total Watts

    It does not matter if there are any amps in the Neutral Wire or not.
    I believe the Neutral Wires are simply connected to a Lug inside the Meter Box.
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #7
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    I believe @solarking is in India so no split phase involved .
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #8
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    I wonder if it's a power factor related meter function (KVA vs Kwh)?
    Off-grid.  
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  • mvas
    mvas Registered Users Posts: 395 ✭✭✭
    edited June 2017 #9
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    solarking said:
    why there are neutral and live amps reading on electric meters? what is the real purpose of neutral amps
    Can you reply with a URL link to an image showing schematic diagram of Power Pole Transformer, Power Meter and Main AC Panel.
    The Grid in India appears to supply 230 Volts 50 Hz AC Residential.
    Do you use 2 prong plugs or 3 prong plugs? ( BS-546 )

    If your neutral wire is bonded to the ground wire then
    I do not see why the Power Meter needs to measure the amps in the Neutral Wire.

    The energy (kwh) consumed by the residence can be determined by measuring the amps in just the Hot Wire & Volts.
    Maybe, they want to verify that you are, in fact, using the Neutral Wire as your return and not the safety ground wire?
    If there is a difference beteen Hot & Neutral amps then you have safety issue?
    In the USA, our Power Meter does not measure the Neutral Amps, so this is very hard to solve.
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  • mvas
    mvas Registered Users Posts: 395 ✭✭✭
    edited June 2017 #10
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    Below is a page from the India - 2011 National Electrical Code
    The Single Phase Energy Meter appears to measure ...
    1) The AMPS in the (P)ower wire only and
    2) The VOLTS between the (P)ower wire and the (N)eutral wire
    And I did not see any diagram showing where or if the (N)eutral Wire is ever bonded to the Ground Wire.
    The (N)eutral WIre typically connects to the common of a 3-Phase WYE on the Power Pole
    I  do not see the answer to the OP's question "Metering amps in the neutral wire" in the India 2011 NEC.
    Maybe the OP has newer Power Meter?


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  • solarking
    solarking Registered Users Posts: 67 ✭✭
    #11
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    my meter looks like this
    https://www.youtube.com/watch?v=zJIxf9aGc0k


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  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #12
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    You guys are probably correct and I am miss-remembering (aka "wrong"). The split phase meters do not measure current in the neutral leg.

    Because the Neutral is (in the US) bonded both at the pole and at the main panel, there are possibilities for parallel current paths (through ground paths) that would make reading the neutral current inaccurate for billing.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Lumisol
    Lumisol Registered Users Posts: 374 ✭✭✭
    edited June 2017 #13
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    Not sure why they monitor the neutral, the billing is off volts and amps used.
    I have heard of unscrupulous users taking the 12 volts off a phone line to run 12 volt loads illegally before though, so maybe they are looking for something similar?
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  • solarking
    solarking Registered Users Posts: 67 ✭✭
    edited June 2017 #14
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    Why does the meter shows negative watts(showing minus sign while displaying watts)
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  • solarking
    solarking Registered Users Posts: 67 ✭✭
    #15
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    Main causes of neutral reversal and ground fault ? how to troubleshoot
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #16
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    Lumisol said:
    Not sure why they monitor the neutral, the billing is off volts and amps used.
    I have heard of unscrupulous users taking the 12 volts off a phone line to run 12 volt loads illegally before though, so maybe they are looking for something similar?
    It's actually supposed to be close to 40V, and if you load it down too much, you get 12V, and the phone co will eventually bust you.
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  • solarking
    solarking Registered Users Posts: 67 ✭✭
    #17
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    BB. said:
    You guys are probably correct and I am miss-remembering (aka "wrong"). The split phase meters do not measure current in the neutral leg.

    Because the Neutral is (in the US) bonded both at the pole and at the main panel, there are possibilities for parallel current paths (through ground paths) that would make reading the neutral current inaccurate for billing.

    -Bill
    Hi Bill,

    what is the main reason for neutral reversal and ground fault? Sometimes it shows reversal and ground fault what could be the reason?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #18
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    What do you mean by neutral reversal?

    The two reasons a utility meter would read negative.

    First is the power in and power out leads are reversed.

    Second is a power source (gt inverter, synced genset, even an induction motor driven by a gasoline/diesel engine) can drive power backwards through the meter.

    Is this single or three phase meter?

    - Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • solarking
    solarking Registered Users Posts: 67 ✭✭
    #19
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    BB. said:
    What do you mean by neutral reversal?

    The two reasons a utility meter would read negative.

    First is the power in and power out leads are reversed.

    Second is a power source (gt inverter, synced genset, even an induction motor driven by a gasoline/diesel engine) can drive power backwards through the meter.

    Is this single or three phase meter?

    - Bill
    I think I have it is phase reversal.

    Strange thing is on my 12v inverter I get the phase reversal and ground fault but if I use 24v  inverter I get no reverse current issue on the utility meter.

    It is a single phase meter, power factor on metes shows .75 sometimes .65 is it worse?
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