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transfer switches + theory

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  • transfer switches + theory

    Hi all,
    I was hoping to get some insight on something I dont quite understand.
    When Installing transfer switches " like the small gentran manual ones".
    I understand that the 3 position switches isolate the hot legs so they do not backfeed into the utility lines. I also understand that in a 240 volt circuit that the neutral carries the unbalanced portion of the load from the two hots. What I dont understand is why doesnt the neutral backfeed into the utility lines, the neutrals from the transfer switches are not switched and hook to the busbar in the panels with the other neutrals, sooo why doesnt the unbalanced portion of the neutral carry into the utility lines. Is it because it returns to the source? Any and all insight into this will be greatly appreciated.
    Thanks in advance.

  • #2
    Re: transfer switches + theory

    I believe the reason is that is is all common, or on it own equipotential plane, jsut as the high voltage lines there "neutral" wires that are grounded, and if you go to the transformer you will see the high voltage lines and the 240/120 volt lines connected to the same ground rod many many times, also there is not a return path for the electricity to flow to energize the transformer.

    First, jsut as in a gfic that measures the current flowing through both wires and will trip if there is a difference between the flow, you need an equal flow out as well as back into the power source, either it be the generator or the power grid.

    Also in the transformer, the neutral wire is grounded/earthed on the transformer pole and at the meter usually, so the induced power would flow to the ground/earth first, and if the hot wires are disconnected (transfer switch) from the transformer, (240/120) side where is the power to flow to energize the opposite coil in the transformer, and make the high voltage wire energized, if there was a flow of power in the neutral it would either follow the ground wire back or the earth it self back to the source.
    You would have to have a flow of power through the power transformer to make the transformer work to energize the line. and if the transfer switch is working and it properly disconnecting the flow of energy off the hot or ungrounded/earthed lines it can not step up power to energize the line.

    unless there is a wiring error that some how creates an unbalanced line and would be some how feeding current in excess out on the neutral and some how travels down the main line, which would have to result in more flaws in the high voltages on the grounds, as the potential on the ground wire would have to be above the potential in the ground and have a flow of electricity between the ground wire and the neutral wire, on the high voltage lines and most are grounded/earth at lest ever four poles,

    so first of all you would have to have some extreme problem where the flow of electricity would flow from the generator out of the local system, (house or business that is on generator power), down the main line and then some how return on some other system back to the generator, as it is the power source,

    and then again you would have to have the grounding system a total disaster on both the local system and the power grids system, either not grounded or many many improperly grounded or multiple paths of return to the generator, and they would have to extend down the main line to where some thing would have created a return path for the power, and create an unbalanced equipotential plane, (it would be similar to stray voltage, look up in the code book on swimming pools and agriculture buildings for livestock, but most of the time that exists because of the distance from the power plant or substation and the resistance in the power lines and voltage is flowing back to the substation via the earth and improper grounding and bonding, but again that is usually in very low voltages),

    but even if it was introduced to the power line on the neutral line, since the line is grounded/earthed (in our area ever pole and I think at least ever 4 poles from my reading at a min.), I would think it would be very difficult to set up a alternate return path that could hurt some some one, as they would be on the same potential as any voltage in the neutral wire. And it would be no different than you touching the case on a grounded tool that is plugged in. (again look up bonding and equipotential plane)


    If it is wired as a separately derived system the neutral is to be switched.

    If the neutral is not switched it can not be considered as a separately derived system,
    thus each system is to ground and bonded according to it type.
    or that is my understanding.
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    • #3
      Re: transfer switches + theory

      Thank you for the info, I feel I have a much better understanding of it now.