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I have a "Little Giant" condensate pump VCMX-20 model. This pump comes with a "safety switch". The pump turns on when the water level gets to 1.2 inches. The "safety switch" will "do something" when the water level reaches 2.2 inches.

Right now I don't have the "safety switch" connected... because I don't know how to connect the "safety switch". I want to connect the "safety switch" to turn off a wall outlet (used by a dehumidifier).

The manual is pretty short when describing the "safety switch":

  1. Safety switch: The safety overflow switch should be connected to a ClassII low voltage circuit. To control a thermostatic circuit the COM and NO connections from the safety switch are to be wired in series with the low voltage thermostat circuit to shut down the heating/AC circuit. The COM and NC switch contacts may be used to actuate a low-voltage alarm circuit (connected in series) if the heating/cooling system can not be disrupted. The safety switch comes from the factory with leads connected to the COM and NO switch terminals.

NOTE: When installing or replacing the safety switch, make sure that it is positioned between the two ribs on the motor cover (Figure 5).

For hook-up of NC circuits see Figure 5. figure-5

The "safety switch" has two wires hanging out.

I opened up the "safety switch" because the wires aren't labeled and found out there is:

  • one wire labeled "NO"
  • one wire labeled "COM"
  • one connector labeled "NC" without a wire
  • front
  • back

How do you connect the "safety overflow switch" wires to turn off a wall outlet??

The manual says to connect the "safety switch" to a "class-II low voltage" device. So maybe there is a "class-II voltage" device that controls the "wall outlet plug".

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  • In a different question the person found what looks like a "class-II" wall outlet switch. I'm not sure if this would work because the device does not have listed any "NC" or "NO" or "COM"... also the item is out of stock. Jun 11, 2017 at 16:42
  • The wall outlet switch that you link in the above comment would do the trick. However it appears to function only in normally open mode. Your safety switch can provide a normally closed signal and the answer from Harper makes a useful note that "normally closed" provides an added failsafe layer. So it's worth finding one like that. Normally closed means that MOST failures of the safety switch itself will result in your device shutting down. Unless the switch gets stuck in the closed position :)
    – jay613
    Jun 18, 2021 at 12:46
  • The same manufacturer as your link makes the CN-15MP which has control of NO/NC and some other cute options. The advantage of this approach versus building your own by buying fan relays or other relays and enclosures is that the safe interface between high and low voltage parts is taken care of by the manufacturer.
    – jay613
    Jun 18, 2021 at 13:16

3 Answers 3

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You just need a relay that includes an integral 24V transformer. There are several of those on the market. By "market" I mean the market of products intended and listed for use in mains electrical; the ones I'm thinking of mount in a 1/2" knockout in a junction box.

You would probably want to move the safety switch wire to the NC position so that it contacts until an overflow. That way if it becomes disconnected it will fail safe.

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  • The manufacturer that OP links in a comment provides a suitable device with certain benefits. It does not require 24V power and it provides control terminals on the outside in a way that does not require OP to exit control wires from inside a junction box to his device. I like the idea of a non-electrician being able to do this without buying kit parts. I've also seen solid state relays that use NO/NC terminals to switch AC input to output, also without 24V power. Seems useful in this application to avoid introducing 24V since nothing inherently needs it.
    – jay613
    Jun 18, 2021 at 13:35
  • @jay what the person proposed there appears to be the same thing I proposed, simply in another form-factor. Jun 19, 2021 at 0:39
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To expand on @Harpers answer (which is what I would do). What you have inside of your pump is what we normally call a dry set of contacts (a single pole double throw switch). Of course the "C" stands for common and "NO" normally open and "NC" normally closed. The switch contacts are only rated for voltages less than 50V. So the transformer is used for the control voltage and we install a pilot relay that has, in this case, a 24V coil and 125V rated contacts. This pilot relay is used to break the circuit wire to the wall outlet.

IDEC is a popular relay company that manufacture "ice cube" relays and you will need a base for it also, along with some sort of enclosure.

I don't know if this helps but I do hope it gives you an idea of how to make this work.

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  • i am a beginner and so I am very grateful for the explanation of the "NC" and "NO" and your explaining what type of part this is "single pole double throw switch"... now that I know what kind of part this is and the terminology I can start working out the details... before I didn't really have enough info. I have a friend who is an electrician and maybe we can find something on amazon.com or some other vendor. Jun 12, 2017 at 13:30
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I have the same need, to shut down my dehumidifiers if the condensate pump fails. This device seems to be the one: https://www.adafruit.com/product/2935?gclid=CjwKCAjwlrqHBhByEiwAnLmYUJbAaNNw3KGV4i2ozkMXJISXyYBC47YzJXdMOZX8bfo3H5Y9hXAfGRoC-_QQAvD_BwE

It's triggered by a positive signal so sharing the ground (common) and connecting the NC line to the above device would activate the switch in the way we're looking for.

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