I’m looking at retro-fitting a dehumidifier with a condensate removal pump to eliminate the need to empty the bin (daily during the summer); specifically this pump. This pump has a safety switch designed to be connected to a class II low voltage circuit in series with a thermostat circuit. However, the dehumidifier doesn’t have a low voltage thermostat and the humidistat runs on line voltage: Humidifier wiring diagram

Based on this, I’m thinking of replacing the bucket shut-off switch with a relay control that is connected to the safety switch and a step-down transformer. However, I’m concerned that without the expected thermostat (and the resistance that would be associated with it) the current in the circuit would be higher than the relay could tolerate. What size resistor should I be using to replace the non-existant thermostat?

  • \$\begingroup\$ I don't think your explanation of what you are trying to do is clear enough anyone here to understand what you are trying to do. Can you draw a schematic diagram? \$\endgroup\$
    – user80875
    Commented Mar 25, 2020 at 20:55

1 Answer 1


I don't see why you would not just leave the bucket switch in place and ignore the overflow switch in the pump. It performs the same function (shutting off the compressor), just at a higher fill level. That seems to be how it is intended to be used.

If you want to add to the bucket switch (I see zero reason to replace it) you could use the microswitch in the pump to switch the relay to interrupt the power. There is no need of a resistor, if you have a 24VAC relay and a 24VAC transformer. The specifications of that relay appear to be adequate to switch the compressor (18A 277VAC) directly. It may not have a very long life switching a compressor load, but it should never actually actuate unless something is wrong.

Pump microswitch (from manual in your link): enter image description here

Whatever mains-voltage wiring you do on the contact side of the relay (if you should decide to go that way), as well as the transformer primary, has to be kept enclosed, away from water and done to an appropriate standard to be safe.

  • \$\begingroup\$ To put the pump in place, the bucket on the dehumidifier needs to be removed (the dehumidifier is designed for this) so the bucket overflow (which is a simple push-button contact switch that is pressed by the weight of a full bucket) won’t ever be triggered in the event of a pump failure. I’m trying to avoid the noted water risk by replacing the existing switch (which will become non-functional) with an alternative. The mains power pieces will be housed inside the dehumidifier (where there is spare room) to keep it away from the water. \$\endgroup\$ Commented Mar 25, 2020 at 21:15
  • \$\begingroup\$ Sounds reasonable enough. \$\endgroup\$ Commented Mar 25, 2020 at 21:27

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