# Aprilaire 500A Wiring Question



## Krebstar (Mar 21, 2017)

Hello,

    I just purchase an Aprilaire 500a whole home humidifier. While I wait for it to be delivered, I have been familiarizing myself with the installation process. I'm looking at the wiring section and I have a few questions for those who can help. The typical wiring for this unit is to use a 24v transformer off a 110v line. The problem I'm running into is my furnace ( A Lennox CBX27UH-024-230-6-02 Electric Furnace) is on 240v. I don't have any other nearby outlets, so I would have to run a dedicated 110v line just to control the unit.

   I've been doing some research and on the inside of my furnace there is a 24v terminal (R) and a common (C). My question is can I just wire my humidifier directly to those terminals for constant power and forego installing the transformer all together? The thing that has me second guessing is a note in the instructions not to wire the transformer into the blower circuit. I think I'm OK, but the text is bold and scary so I figured I'd ask before assuming .

   My second question is the humidifier control panel calls for a 24v accessory line to be wired into the panel ( I'm guessing some sort of sensing signal?). The directions say to look for a "HUM", "ACC", or "EAC" terminal. Just looking at the schematics my unit doesn't appear to have those terminals. There is however a "ECON" terminal. Would this stand for "External Connection"? It seems to be wired to the 24v and the blower terminal which leads me to believe its only energized when the blower comes on ( correct?). So would this suffice as the 24v acc line I can use? Should I test this terminal with a multimeter while the furnace is running to verify 24v?

   I have attached the wiring diagrams below for both the humidifier and the furnace. Thanks for any help !


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## nealtw (Mar 21, 2017)

Just some dumb questions.
The diagram you posted says for 460 volts?
Where does the furnace get it's 24 volts?
Does your 240 volt cable include a neutral?


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## Krebstar (Mar 21, 2017)

(1) Sorry about that. The manual had the diagrams for both 240v and 480v. The correct one is attached below. Right now I'm assuming its 240v until I can actually get in there and inspect. 

(2) From what I can see it looks like the furnace has a built in transformer to create the 24v (T1). 

(3) I haven't torn apart the furnace itself yet to see what the actual inline wires look like. I can tell you that on the garage wall there is a 2 breaker control box that feeds the furnace. So maybe there are 2 separate 110V lines going into the furnace instead of a single 240v? Or maybe there are 2 110v into that breaker box and 1 240v line out?


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## nealtw (Mar 21, 2017)

240 that does not require neutral can be wired 2 wire with a ground or it can be 3 wire with a ground so you can open that box and see what you have.


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## Snoonyb (Mar 21, 2017)

Note #2 talks about ampasity and over current protection.

So what is the size of the breaker and what is the "operating" current of the furnace?

What is the 24V current load of the dehumidifier?

120V single phase is 1-hot, 1-neutral and  grnd. and commonly referred to as a hot pair.

240V single phase, in todays version of general appliance wiring, is 2-hots, 180 out of cycle from each other, 1-neutral and a grnd.


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## Krebstar (Mar 21, 2017)

I will verify the breaker when I get home. There is a chart on the front of the unit listing amperage. I'll snap a picture when I get home. I will also see if I can figure out what the wire combination coming into the unit is. 

  I will say that I really don't want to mess with the incoming power to the furnace if I don't have to. Worse case I'd rather just pull a new 110v line from an existing outlet. I was just curious if I can power the humidifier right from the furnace before I go through all that trouble first. 

The Humidifier operating specs are 24 VAC ~ 60hz @ .5A. Thanks for the replies so far !


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## nealtw (Mar 21, 2017)

I will leave the tech answers to the pros but I would think you could run a low voltage to the nearest 120 supply.


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## Snoonyb (Mar 21, 2017)

Krebstar said:


> I will verify the breaker when I get home. There is a chart on the front of the unit listing amperage. I'll snap a picture when I get home. I will also see if I can figure out what the wire combination coming into the unit is.
> 
> I will say that I really don't want to mess with the incoming power to the furnace if I don't have to. Worse case I'd rather just pull a new 110v line from an existing outlet. I was just curious if I can power the humidifier right from the furnace before I go through all that trouble first.
> 
> The Humidifier operating specs are 24 VAC ~ 60hz @ .5A. Thanks for the replies so far !



Thanks.

At .5A you have several option without affecting the existing systems warranty.

You can add another 240/24V stepdown transformer before your system, or a 120/24V stepdown transformer off of one of the 240V legs, but only if there is a neutral present.


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## Krebstar (Mar 22, 2017)

Hi everyone,

 I was rooting around last night in my utility room and I think I'm just going to hard wire the transformer. I think its going to be the easiest route and its what the manufacturer recommends. There is a nearby light I can tap into and At only .5A for the unit, I think it would be OK. This way I'm not messing with any existing wiring into the Heater. Thanks for all your help !

I guess my second question about the ECON terminal is still out there if anyone can chime in. I can't find any info on what the ECON terminal even is.  Anyone have experience with Lennox products?


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## Snoonyb (Mar 22, 2017)

Be sure you are powering the transformer from the hot pair, and not the switch leg.


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