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Removing voltage from a circuit

Discussion in 'General Electronics Discussion' started by Ira, Mar 2, 2010.

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  1. Ira


    Mar 2, 2010
    I have a micro-switch (picture to follow in second post) in a generator automatic transfer switch (ATS). The COM terminal (almost) always has 120vac going to it. The NC terminal is used by the ATS, but the NO terminal is unused.

    I want to somehow hook the NO terminal to a zone on a security panel so I can tell the state of the micro-switch. In a perfect world, I would simply tap on to the COM terminal and run a wire to one side of the zone input and run a wire from the NO terminal to the other side of the zone input. The problem is that the security panel zone can't tolerate any voltage. It expects the zone to be a simple dry contact setup.

    A partial solution would be to use the 120vac present to operate a relay, then connect the relay contacts to the zone. The problem here is that there may be times where there is no power at the COM terminal, but I still need to determine the switch state.

    So my question there a way to "remove" all the voltage from a wire tapped on the COM terminal (if voltage is present) without affecting continuity/resistance, but still be able to sense open/close of the switch? In other words, when the switch is open, the loop will be closed and there will be no voltage on the loop. Also, it needs to have no effect on the existing circuits.
  2. Ira


    Mar 2, 2010
    This is a picture of the micro-switch.

  3. Resqueline


    Jul 31, 2009
    For sure, it can be done, but it's somewhat elaborate. I'd rather figure out a way to add an extra microswitch if at all possible.
    You'll need to add an extra (low voltage, insulated) stand-alone always-on power source. Wire it into the COM terminal, then from the NO terminal and into a relay (or an opto-coupler) and from there back to the power source.
  4. 55pilot


    Feb 23, 2010
    Which ATS are you using? Many Generac ATS have a place to mount a completely independent switch for a low voltage circuit. The switch is mechanically activated by the position main transfer bar.

    That is the route I would examine first.

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