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    JG1489's Avatar
    JG1489 Posts: 4, Reputation: 1
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    #1

    Apr 16, 2014, 11:50 AM
    CHALLENGING QUESTION: Low-voltage switch in a high-voltage circuit?
    A project I'm working on has an air pump and a water pump that run during operation. When the water tank that the water pump draws from becomes empty, a liquid level switch will be used to shut off both pumps. The original plan was to just place the switch in series with the power supply for the pumps. The system draws power from a wall outlet; 120 VAC and 20A max load.

    However, after contacting the manufacturer of the switch, I was told:
    The M8700 is a low voltage switch and can only see .28amps of current. You would have to use a relay or some type of switch protection for this switch. Please see the attached.
    The attachment the representative gave me suggested using a Varistor V130LA10A across the switch.


    My question is: what exactly would I need to do wire this switch into my system? It might be worth noting that the pumps are both wired to a single toggle switch.
    smoothy's Avatar
    smoothy Posts: 25,492, Reputation: 2853
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    #2

    Apr 16, 2014, 11:53 AM
    Add a low voltage transformer and a relay to control the larger current... higher voltage controlled by the liquid level switch
    JG1489's Avatar
    JG1489 Posts: 4, Reputation: 1
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    #3

    Apr 16, 2014, 12:44 PM
    Thanks for the prompt reply. Since I have very limited knowledge on this subject, could you explain in detail how I would wire these into my system? What specifications should I look for in the transformer and relay?
    JG1489's Avatar
    JG1489 Posts: 4, Reputation: 1
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    #4

    Apr 21, 2014, 02:34 PM
    Is there any more feedback I can get on this issue? Thanks!
    Missouri Bound's Avatar
    Missouri Bound Posts: 1,532, Reputation: 94
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    #5

    May 6, 2014, 06:53 PM
    I see this post is a few weeks old. This is the first time I saw it. Did you get an answer yet? It's possible you can use an HVAC type control to make this work. What it does it provides control over a line voltage circuit by using an internal transformer and allowing a low voltage switch to control the circuit. An example would be a relay which your thermostat controls to turn on your furnace, boiler etc. Generally there are terminals to connect the high voltage wires to, then a couple of terminals to connect a low voltage switch to.
    JG1489's Avatar
    JG1489 Posts: 4, Reputation: 1
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    #6

    May 8, 2014, 09:24 AM
    Thanks for the reply. I'm actually getting some help from an electrical contractor to deal with this issue and some other electrical concerns. I believe he will be using a relay.
    Missouri Bound's Avatar
    Missouri Bound Posts: 1,532, Reputation: 94
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    #7

    May 9, 2014, 07:21 AM
    OK. Best of luck.
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