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Old 01-11-2010, 01:18 PM   #1
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Basic wiring question


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.

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Old 01-11-2010, 04:13 PM   #2
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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.

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Old 01-11-2010, 06:49 PM   #3
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scarpen01 you are exactly correct
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Old 01-11-2010, 07:33 PM   #4
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what he said!
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Old 01-11-2010, 07:37 PM   #5
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I replaced my transformer and it reads 26 volts does the 2 volts make a difference or just that it is new?
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Old 01-12-2010, 12:43 AM   #6
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Originally Posted by jmhai View Post
I replaced my transformer and it reads 26 volts does the 2 volts make a difference or just that it is new?

no dosent matter and age is irrelivent
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Old 01-12-2010, 08:02 AM   #7
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Basic wiring question


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
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Old 01-12-2010, 10:03 AM   #8
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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.
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Old 01-12-2010, 10:39 AM   #9
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Originally Posted by H. Phillips View Post
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.
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
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Old 01-12-2010, 04:10 PM   #10
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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.
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Old 01-12-2010, 09:46 PM   #11
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Originally Posted by veesubotee View Post
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
when its not calling for heat there is no voltage to white wire
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Old 01-12-2010, 11:21 PM   #12
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Quote:
Originally Posted by veesubotee View Post
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
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?
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Old 01-13-2010, 01:00 PM   #13
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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?
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
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Old 01-13-2010, 01:46 PM   #14
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Basic wiring question


Quote:
Originally Posted by veesubotee View Post

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.



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.



V
Bet those aren't dry contacts.
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Old 01-13-2010, 03:32 PM   #15
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Originally Posted by beenthere View Post
Bet those aren't dry contacts.
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


Last edited by veesubotee; 01-13-2010 at 03:44 PM. Reason: typo
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