I just bought an Aprilaire 58 digital humidistat (I believe this humidistat comes standard on Aprilaire humidifier models 600 and up) to install on my existing model 550 humidifier. I think I understand the instructions pretty well, except a couple things.
The instructions say it needs a constant power source. The humidistat runs on 24v, so it has a transformer. The instructions say:
"Wire the external 24 VAC transformer into a constant power source other than the heating, ventilating, air conditioning equipment (HVAC) blower circuit. The transformer can be powered off the 120 VAC line at the junction box before it enters the HVAC."
I'm no electrician, but I'm guessing that means I can just wire the transformer into the electrical box that has a switch to allow power to the furnace.
It doesn't say much more about the transformer than that. The transformer has two leads that go to the 120v power source, an odd angled screw (looks too thick to be for a ground wire and it's not colored green) and then on the other side, the terminals to run the 24 volts to the humidistat.
I'm planning to put this transformer in a metal box, near the switch to the furnace. However, what is the angled screw for on the transformer? Is this used to somehow mount the transformer in a metal electrical box? But if it was for that purpose, I don't know why they'd angle the screw. Or am I mistaken ... that this is the ground screw?
If anyone can advise if my wiring plan sounds good and what this mysterious angled screw is for, I'd appreciate it. Thanks for the help!!