Whole house humidifier: old switch too many amps for HUM terninal

[bryanscholtes]

How can I get my old 120V whole house humidifier setup to turn on only when heat is on?

I have an old General 1040 bypass humidifier with a 120V solenoid, wired to an ancient Sears 120V humidistat switch.

Right now the humidistat switch AND humidifier are wired to the furnace?s 120v switch.

Therefore, whenever the furnace is on and the humidistat is set above ?of f?, the humidifier runs constantly even when the fan is off. Water runs c onstantly.

My old Goodman GMP-075 furnace has a 115V HUM terminal. I believe the ratin g is 1.5A. I?d rather connect the humidistat to the furnace 115V HUM ter minal, but the Sears humidistat draws 6A. The humidifier solenoid is only 6 watts, so draws only .05A.

Is there any way to draw humidifier solenoid power ONLY from the HUM termin al, and humidistat power ONLY from house 120V? This would avoid overloading the HUM terminal, but I don?t know how the humidistat would signal the h umidifier to flow. Otherwise, is there another wiring setup that can draw 115V at 7A, and only kick on when heat is energized?

I see the White-Rodgers 2271-100 humidistat switch only draws .5A, but I? d rather avoid buying new equipment.

[The Daring Dufas]

If you're able to assemble simple electrical items, you can put together a box with a contactor having a 120vac coil and use one or two of the contacts to switch the higher current. It's basically a high current auxiliary relay to control the high current load. The 120vac coil that operates the contactor/relay draws very little current. There could be something ready made and I believe I've seen and used as a lighting relay to operate mutable overhead lights drawing a higher current than a regular switch will handle. You could check with an electrical supply house to see if you can obtain one already built which has screw terminals for you to hook up your higher load to be controlled by a low current source. ^_^

TDD

[Tony Hwang]

Hi, Just move the 120V take off wires to the blower supply leads. Then it'll run only when blower is running. Another is using sail switch mounted inside duct. But I like the first idea.

[makolber]

Just be aware that if the blower is wired to run at multiple speeds, and you wire the humidifier circuit to the blower, it can act as a transformer and apply more then 120 V to the humidifier which is not a good idea.

If you wire the humidifier across the highest speed winding of the blower, then the voltage will be 120v or less in all cases.

Or rewire the blower to run at only one speed (high speed for example) and wire the humidifier to that same winding.

Mark