Basic wiring question

veesubotee

What is the voltage read across W & C at the furnace? 24 volts?

Is C normally hot and W becomes hot (or visa-versa) with a call for heat?

Thanks.

scarpen01

In my recent learning curve of the transformer and its associated wiring, the "hot" is the R going to your thermostat. when the call for heat is switched it then travels back in the W. The C is the common or the ground. However, I will not pretend that I am an expert by any means. It is simply my understanding as I just had to figure out the intracies of the transformer this weekend.

tk03

scarpen01 you are exactly correct

plummen

what he said!

jmhai

I replaced my transformer and it reads 26 volts does the 2 volts make a difference or just that it is new?

kennzz05

no dosent matter and age is irrelivent

veesubotee

Thanks to all who responded.

Just one follow-up question: Am I correct that with NO call for heat, there would be zero (0) volts measured between W and ground?

Thanks.

V

H. Phillips

You should get 24 volts from the W to ground. If you measure across the controlled device, such as a gas soloniod you will get the voltage drop across the device, which is much smaller. Not 0 but it could be less than one volt.

veesubotee

Just to be sure, I stated that there was NOT a call for heating.

As Scapen01 stated:

"in my recent learning curve of the transformer and its associated wiring, the "hot" is the R going to your thermostat. when the call for heat is switched it then travels back in the W. The C is the common or the ground."

So, would you agree that under my circumstances, there would be no voltage (W to ground)?

V

tk03

You should in theory have "0" volts. There may be a bit of backfeed from somewhere and have a slight reading.
The 26 volts is not uncommon. Iron core transformers work with voltage in and voltage out. They step down from 120v nominal to 24vstep nominal. If the incoming goes up the outgoing goes up and if the incoming goes down the out going goes down.
It can operate anywhere between 20 and 30 volts.
The way it works is this

wStep-Down – Primary 120v would have about 5 times the windings as the 24v side. To determine the winding change divide the incoming voltage by the what voltage you want out. In this case a 120v to 24v would look like this,
120 / 24 = 5 times more windings on the secondary side than the primary side.

plummen

when its not calling for heat there is no voltage to white wire

H. Phillips

Yes, but I thought you might be unsure of why you are reading something else. You are unsure of the voltage, or that you are reading between W and C?

veesubotee

Actually, I'm not reading anything.

My question was posed based on a theoretical situation, which I will describe.

I have a Rheem Modulating furnace. I am thinking of adding an Aprilaire humidifier, Model 700. The power requirements are: Line voltage for the fan motor, 24 volts constant power for the automatic humidistat, and connection to the W & C terminals on the furnace board, which I assume, supplies 24 volts on a call for heat only.

The furnace board has 2 HUM terminals, which are 'dry contacts', i.e., they are a board-controlled switch, which closes on a call for heat.

Since the Mod stats can be tempermental (I had one replaced due to drooping room temperature), I don't want to make any active connections to the board, which might conflict with proper furnace operation and possibly compromise my warranty. Ironically, my present stat started to flake out yesterday.

So what I was proposing to do was from the (Aprilare) supplied transformer, 2 wires (constant power) to the humidistat, 2 wires from humidistat (intermittent power) wired in series to HUM contacts and transformer secondary (loop).

Comments on the above are welcomed.

Incidentally, I would also be interested in comments from Rheem/Ruud PROs regarding my thermostat problem. Specifically, on morning recovery, after the stat reaches set point and stabilizes (usually after 30 - 60 minutes), the very low speed operation will cease. Sometime later, the furnace will restart and run at a much higher rate, which is unusual for the morning period. Checking the stat, room temp may be 1 or 2 degrees below set point. This is with the 411 stat and only happens randomly at morning recovery.

V

beenthere

Bet those aren't dry contacts.

veesubotee

Beenthere:

Per the RGFD Installation manual (pg59), quote:

"The humidifier contacts (labeled HUMIDIFIER on the IFC are "dry" contacts on the IFC. This means that the terminals are connected to the contacts of a board-mounted relay. The coil of the relay is controlled by the microprocessor of the IFC. The coil is engaged roughly any time the heat speed blower is engaged, so that humidification is active any time the heat blower is running."

Been, any comments on my wiring plan in general?

Thanks.

V