NEST install power connection help


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Old 03-06-16, 04:37 PM
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NEST install power connection help

I just installed this tstat and had trouble powering it at 1st. Well I realized I have two tstats hooked up to one boiler. Unhooked one and Nest powers up no problem. But when I hooked other basement one up it(Nest) goes dead. I'm assuming the 24v transformer wont power both but how can I wire in another one. I have a steam boiler setup with a basement hot water loop and have that controlled by a Taco SR503 relay. Thanks
 
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Old 03-06-16, 05:17 PM
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The SR503 does not have a factory setup for powered thermostats. I think there is a work around.

Does your board look identical to this diagram ?
Do you have two screw terminals at the 24vac power location in the upper left hand corner ?
Do you have a voltmeter ?

You WILL need a third wire between the stat and the 503.

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Old 03-06-16, 05:53 PM
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Yes basically same relay. Yes has a 24v built in transformer like diagram.Yes have voltmeter. How would I connect it up. 3rd wire? Meaning "C" common off the transformer? to one of my thermostats?
 
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Old 03-07-16, 04:25 PM
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Should mention also I have a 24 volt auto feeder hooked up to. I think another power source somehow wired up should fix it.
 
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Old 03-07-16, 04:32 PM
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Assuming you have the 3 wires at the Stat,probably red,white ,green , remove the wires from the Stat connect the Green or what ever the spare color is to one of the terminals at the 24 VAC block in the SR503,test between Red and that wire at the Stat,should be 24 VAC if not switch the wire to the other terminal in the SR503 24 VAC terminal block.
 
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Old 03-07-16, 04:39 PM
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It's a little more involved.

Short the Zone 1 TT terminals. Measure from that shorted connection to the 24v power connections. The 24v power terminal that shows 24v from the shorted TT terminals to it is the C terminal.

Now... with nothing on the Zone 1 TT terminals check from your newly labeled C connection to each T terminal. The terminal that now shows 24vac is the R terminal.

The other T terminals that shows no voltage to C is the W terminal.

Please let me know what your testing determines so I can document it.
 
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Old 03-07-16, 06:04 PM
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Oh ok I can try that. Do you know what setting I should have my digital voltmeter on? Its new and havent used one in awhile. Thanks
 
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Old 03-07-16, 06:12 PM
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Set it to the AC voltage scale. If analog.... select the voltage setting just over 24vac.
You could post the make and model of the meter and I could further advise you.
 
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Old 03-07-16, 06:24 PM
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Name:  southwire.jpg
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Size:  41.9 KB This one Southwire 10030S . havent had much luck yet.thanks
 
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Old 03-07-16, 06:55 PM
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Geo- between the 3rd black wire not getting anything. Tried switching from Com/24vac off the block. I am getting 13.1 volts between the Rh n W wire this should be 24v?. thats been sufficent to power the Nest over wifi and remote also but I will have to trouble shoot it another day. Thanks
 
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Old 03-07-16, 06:58 PM
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Oh ok I got the multimeter settings right but not getting the correct voltage needed. If i temporary disconnect my 24v auto water feeder think that may help?
 
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Old 03-07-16, 10:16 PM
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You can use a separate transformer to power the thermostat through the RC and C terminals.

The RH and W would connect to the two TH terminals.

This thread may be of assistance...
http://www.doityourself.com/forum/th...er-system.html
 
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Old 03-08-16, 12:31 AM
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I marked the meter for you. You'll be using the 200v ~ setting.

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Old 03-08-16, 03:33 AM
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Thanks PJ the booklet shows to use the 200v to the left side of center for DC volts. Not sure if it matters AC on the right.?
 
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Old 03-08-16, 03:36 AM
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Thanks Houston but if im getting 13 volts at Rh & W and adding 24 volt transformer to Rc & C wont that be to to much voltage?
 
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Old 03-08-16, 03:50 AM
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I think the transformer inside the SR503 may be shot. I checked voltage between comn 24vac and get nothing. Its warm like normal plus changed the fuse next to it. Theres room in the 503 to mount a new transformer if have to.
 
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Old 03-08-16, 04:25 AM
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RC and RH are separated by the Nest thermostat internally. The important step is to pick up C from the same transformer that powers RC.

This has already been performed many times on this forum.
 
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Old 03-08-16, 04:46 AM
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Ok great Houston. I'll try new transformer. Is the one in the SR503 changeable or better just get a junction box mounted one? How can a test the one in the 503? check between com n 24vac terminals?
 
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Old 03-08-16, 05:37 AM
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Houston I have only 3 wires going to my Tstat. will I have to run another or is there a way I can use just 3?
 
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Old 03-08-16, 09:59 AM
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Sure it matters..... you ARE checking for AC voltage..... not DC voltage.

If your heating system is working normally..... water flowing to heating loops.... then there is nothing wrong with the existing Taco transformer.

If you opt to use a second transformer.... it does not go in the Taco controller and you will also need four wires to the thermostat.
 
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Old 03-08-16, 10:36 AM
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I would try the test as PJ posted before looking into a transformer.

3 wires can work if you get a relay and a transformer. ( A fan center has a relay and transformer)
 
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Old 03-08-16, 10:56 AM
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Ok PJ will use the AC side to measure AC voltage.

I'm not using the transformer from the 503 just the one off the boiler. see pic for the hot water loop.Name:  503_resized.jpg
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I dont really want to run a fourth wire if dont have to.
 
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Old 03-08-16, 11:00 AM
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Yes Houston I'd like to use just 3 wires if possible. That 3rd wire goes to the "C" terminal correct?

I do have a RIBU1C relay also not sure if its needed here ? thanks
 
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Old 03-08-16, 01:34 PM
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Now I'm completely lost.

You're saying the 503 transformer is defective ?
I don't even see 120v connected to the 503.
I don't see a second thermostat wiring.

Is the 503 even doing anything there ?

No need to even bother with the tests.
 
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Old 03-08-16, 05:15 PM
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Its all good now. Well initially had the upstairs Nest tstat connected directly to boiler TT. Now its connected on zone 1(priority) in the 503. Zone 2 hot water loop. Yes I took the N wire off temporary 503 at times. The Taco was jus for the basement hot water loop now runs both tstats. Transformer good in the 503 also. Thanks for your help PJ n Houston.

Only glitch I noticed is the zone lights on the front. Zone 1 is always lightly illuminated. Zone 2 always flickers lightly.But are solid when the zone calls for heat. Maybe normal ?
 

Last edited by mikk1; 03-08-16 at 06:08 PM.
 

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