Electrical – duplex outlet relay

electrical

I want to have the room humidifier operate when the furnace comes on. The furnace is in the
laundry room in a manufactured home. Is there a relay that I can wire into the duplex
outlet to run the humidifier only when the furnace is running?

2/5/14
To clarify my question: The furnace is a Colman Downflow DGAT auto ignition 75000 BTUH model.
Hunidifier is room size, Holmes ultrasonic that reviews state will run 12 hrs. but it can
leave the floor water soaked. If the humidifier is near the furnace, then moisture can be
drawn into the return on the furnace and probably won't saturate the floor, if only operating with the furnace on.
I don't know if a simple relay or controls are available to operate this task, and I would like to ask for specs and instructions.
Thanks for any reply.

Best Answer

You can build a circuit to do what you're asking, though as others have pointed out it's not necessarily the best way.

What you can do is use a 24V AC relay to switch an outlet.

Waring: 120V AC is dangerous and can seriously hurt or kill you. If you're not aware of what the difference between hot, neutral and ground is, or the thought of "exposed terminals" doesn't scare you, stop now. Learn some basic electrical skills, find another way, or enlist the help of a friend.

Get a relay

You need a relay with a 24V AC coil, and which is rated to switch 120V AC (or higher) at 15A (or higher), it just needs to be SPST (single pole, single throw) though DPST or DPDT (double pole, double throw) is fine.

enter image description here

Mount the relay in a box

You need a box to put the relay in to protect it from being touched (since there will be 120V on the terminals of this thing). There are many types of boxes, from metal junction boxes to PVC project boxes.

enter image description here

Figure out some way to secure the relay base down in the box (PVC is a lot easier for this).

Connect power

You'll power this box by plugging it into a regular outlet. You need a power cord and a strain-relief connector.

enter image description here

Get a receptacle

Probably the easiest way to do this is to use the female end of an extension cord and a strain-relief connector. You can actually just buy an extension cord and cut it and half, and use this for the power in and out. You can even use one of the fancy ones with the lighted end, and you'll have an indicator if the relay is on or not.

enter image description here

Otherwise you need a normal receptacle which can either be mounted in this box, or attached via a surface-mount box (aka handy box). If you attach it externally, you'll need to use either armored cable (BX), or extension cord wire (SJO) and appropriate box connectors or strain relief connectors.

Wiring it all up

Here's the wiring diagram for your furnace:

enter image description here (Source)

The relay you get will have a pinout on it, something like this:

enter image description here

Essentially:

  • Connect your furnace W and C terminals to the coil of the relay (terminals 2 and 7)
  • Connect the hot (black) wire from the 120V plug to the power terminal of the relay (terminal 1)
  • Connect the hot (black) wire of the receptacle to the switched terminal (3)
  • Connect the two neutrals (white) together.
    • If you have a DPST relay like this diagram is for, you can optionally switch the white wires by connecting to terminals 8 and 6, mirroring the hot wires. It doesn't really matter.
  • Connect all the grounds together, and if you're using metal boxes, the grounds must connect to the ground screw on the box itself.

That's really all there is to it. When the thermostat calls for heat (powers W terminal), 24VAC will power the coil of the relay, which will turn the receptacle on.

You will likely be able to find all of this at your local box store. If they don't have relays, a local trade electrical or industrial supply store likely will, and I hear this internet thing sells stuff now too.

Good luck.

Related Topic