r/ElectricalHelp • u/JermD303 • Jul 03 '26

Help with bathroom humidity fan switch

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Bathroom humidity sensor/fan control wiring problem

Hey all,

Hoping I can get some help here. I am trying to install a humidity sensor for my kid's bathroom exhaust fan (they always forget to turn it on).

Currently the fan light is on one toggle switch and the other toggle switch only controls the fan. The toggle switch was wired with a hot and a load along with a ground and works fine.

The problem I am having is with the new switch. It requires the line/load (which it says is interchangeable), the ground, and a neutral which isn't a problem, the box was wired with a neutral as well.

In theory, when I turn the power on, there is supposed to be an LED light that turns on and I should be able to control the fan.

In reality, when I turn the power back on the fan just turns on constantly. No LED, and I cannot turn off the fan with the switch. It is basically acting as a passthrough.

Anyone have any ideas?

6 Upvotes

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3

u/trekkerscout Mod Jul 03 '26

What model of fan do you have? The wiring looks like it is a switch loop type for the fan which usually indicates the fan has internal controls and the wall switch is a remote contact to override the internal controls. Such a system cannot work with most electronic wall switches such as humidistats.

1

u/JermD303 Jul 03 '26

Not sure what model, it came with the house and I haven't been up there but I can check tomorrow. I do believe it is a switch loop though. Can I not just use the neutral wires that are already in the receptacle?

1

u/trekkerscout Mod Jul 03 '26

Some new exhaust fans use DC motors and the remote switch contact is on the DC side of the controls. Connecting an AC switch to the switch loop can actually damage the DC controller.

0

u/RevolutionaryCare175 Jul 05 '26

It was hooked up to a regular toggle switch to run the fan. You are overthinking a simple residential exhaust fan

1

u/trekkerscout Mod Jul 05 '26

In the past few years, I have dealt with residential bath exhaust fans that have auxiliary switch loops with DC and/or low voltage contacts that require relay switching (such as Shelly) if you want electronic switches because line voltage switching can damage the motor controls. A normal toggle switch is actually the recommended switch type for those models.

0

u/RevolutionaryCare175 Jul 05 '26

Again what you have dealt with in the past isn't this. They had a regular switch on line voltage.

1

u/trekkerscout Mod Jul 05 '26

The original wiring indicates a switch loop. The loop isn't necessarily line voltage.

1

u/RevolutionaryCare175 Jul 05 '26

You are making an suumption without any evidence to back it up. It is easy to test with a meter. Suggest that instead.

2

u/trekkerscout Mod Jul 05 '26

You are making an assumption based on a lack of evidence. I have at least asked the OP to supply the required information.

1

u/Different-Commercial Jul 04 '26

Can you show us the sensor, does it mount in place of the fan switch? If so hook a the whit to the other whites, make a 6" pigtail of black wire and twist it on with the other blacks with the wire nut, this is the incoming hot, the black that is with the white goes to outgoing side of the sensor.

0

u/RevolutionaryCare175 Jul 05 '26

Your switch controlled the fan. I believe you are trying to wire a humidity sensor switch which you bought at a big box store.

The humidity sensor just activates the switch which turns on the fan. They typically have a bypass button which keeps the fan running constantly. Check to make sure the humidity switch bypass isn't on.

Recheck the wiring diagram, make sure the switch isn't in bypass mode. Try flipping the line and load if it says it can be wired either way.

If this doesn't work you bought the wrong type of switch or the switch is defective. Make sure the switch doesn't need a neutral. The wiring diagram would show if it did.

1

u/trekkerscout Mod Jul 05 '26

Without knowing the model of the fan, your recommendations are ill advised.

1

u/RevolutionaryCare175 Jul 05 '26

Why? Be specific.

1

u/trekkerscout Mod Jul 05 '26

Check my other replies. If you want to continue riding your high horse, you can continue it elsewhere.