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Another Common Wire Question

TheStressMachine
TheStressMachine Member Posts: 39
edited September 2021 in Thermostats and Controls
Hi there, tried to read as much as I could here but had some specifics I couldn't figure out from the posts.

I'm looking to get a common wire into this system to install 2 smart t-stats, wiring diagram here.

It seems like the common wire is just a neutral in basic terms, so I thought I could wire the two TSTAT commons to the the transformer neutral and call it a day, but I'm not sure if it's better/required to wire them to the common on the boiler control? Also, a few other things confused me:

I thought L1 on a transformer was hot, but the wiring has the white wire going from TR to L1 per the instructions. Is L1 the Neutral?

I can't find any labels on my transformer, are there labels on the box side if I were to unhook it? If not, how can I tell how big it is? Also how big do you recommend for 3 taco valves and 2 smart thermostats?


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Comments

  • JakeCK
    JakeCK Member Posts: 1,356
    Sounds like this is wired old school between the t-stats and valves. Have you considered a zone valve controller? Something like a tekmar 303v. It will have its own power supply and will provide a c wire terminal. The 303v is a 3 zone controller with priority for DHW. Simplifies wiring and diagnostics when s*** breaks.
  • TheStressMachine
    TheStressMachine Member Posts: 39
    JakeCK said:

    Sounds like this is wired old school between the t-stats and valves. Have you considered a zone valve controller? Something like a tekmar 303v. It will have its own power supply and will provide a c wire terminal. The 303v is a 3 zone controller with priority for DHW. Simplifies wiring and diagnostics when s*** breaks.

    I haven't, but mostly because I'm not qualified enough and trying to stick to DIY. Are you saying getting a common incorporated in this configuration isn't doable?
  • JakeCK
    JakeCK Member Posts: 1,356
    No its certainly possible. You just have to be certain the smart tstats don't over tax the transformer. And a lot of the wifi, bluetooth LE, and zigbee ones are good for that. With wifi being the most power hungry. Z wave isn't too bad, Those t stats can actually run off AA batteries for a year or two.
  • JakeCK
    JakeCK Member Posts: 1,356
    That said wiring in a c wire to that could be harder then installing a zone controller. The zone controller handles all the logic for you.
    Zman
  • TheStressMachine
    TheStressMachine Member Posts: 39
    JakeCK said:

    No its certainly possible. You just have to be certain the smart tstats don't over tax the transformer. And a lot of the wifi, bluetooth LE, and zigbee ones are good for that. With wifi being the most power hungry. Z wave isn't too bad, Those t stats can actually run off AA batteries for a year or two.

    Thanks, I'm trying to install an ecobee. The spare wire is in the bundle to the t-stats. What size transformer do you think I need? Also you mention it could be hard, does this mean it's not as easy as wiring the common to the transformer neutral or the common on the boiler board?
  • JakeCK
    JakeCK Member Posts: 1,356
    I don't know what size transformer. depends on the hardware attached to it. How many ecobees are you installing?
  • TheStressMachine
    TheStressMachine Member Posts: 39
    JakeCK said:

    I don't know what size transformer. depends on the hardware attached to it. How many ecobees are you installing?

    Two total, one on each T-Stat driven zone. The third zone is to my indirect hot water heater so don't think I need to do anything there.
  • JakeCK
    JakeCK Member Posts: 1,356
    edited September 2021
    If I'm not mistaken ecobees use wifi. Two of them might bee too much for your transformer. I would suggest a separate transformer for that reason alone. I think I read somewhere they use 2amps max on a 24v transformer.

    2 amps each***
  • JakeCK
    JakeCK Member Posts: 1,356
    edited September 2021
    I was doing some reading, I think that amp draw is wrong for the ecobee. That's a lot of power. Their install says you need a 24v transformer with 2 amps max, not that it draws that. 2amps at 24v is 48watts. Thats a lot of juice for a t-stat.
  • TheStressMachine
    TheStressMachine Member Posts: 39
    JakeCK said:

    If I'm not mistaken ecobees use wifi. Two of them might bee too much for your transformer. I would suggest a separate transformer for that reason alone. I think I read somewhere they use 2amps max on a 24v transformer.

    2 amps each***

    Thanks again, it's much appreciated.

    Assuming I get an appropriately sized transformer, should I connect the common terminals from the T-Stats to the neutral of the transformer? Or should it be to the Common terminal on the boiler controller?
  • JakeCK
    JakeCK Member Posts: 1,356
    I'm not an expert and I really don't want want to give you bad advice. Lets see what some of the experts say.
    TheStressMachine
  • JakeCK
    JakeCK Member Posts: 1,356
    edited September 2021
    And let me put it this way, I had the same issue. I added a second hardwired transformer that is separate from the boiler. And the t-stat(honeywell T6 Pro with z-wave) can run off batteries. This means if the transformer for the t stat blows up, it doesn't affect the boiler and the stat falls back on batteries as just a dumb digital stat. I still have heat, and my boiler isn't damaged.
    TheStressMachine
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 14,505
    edited September 2021
    @TheStressMachine

    Your wiring diagram doesn't look right. Is that the actual diagram or something someone drew?? What model is your Taco valve?
    JakeCK
  • JakeCK
    JakeCK Member Posts: 1,356
    edited September 2021
    @TheStressMachine Your wiring diagram doesn't look right. Is that the actual diagram or something someone drew?? What model is your Taco valve?
    I was thinking the same thing. That diagram doesn't make sense.

    I was thinking to my self "I don't think that works like that but ok, what do I know" Why I didn't want to give him wiring advice and cause him to let out the magic smoke.
  • TheStressMachine
    TheStressMachine Member Posts: 39

    @TheStressMachine

    Your wiring diagram doesn't look right. Is that the actual diagram or something someone drew?? What model is your Taco valve?

    I drew it based on the wiring I see. What doesn't look right? The model is AG13A01A. Here's a picture.
  • TheStressMachine
    TheStressMachine Member Posts: 39
    JakeCK said:



    @TheStressMachine

    Your wiring diagram doesn't look right. Is that the actual diagram or something someone drew?? What model is your Taco valve?

    I was thinking the same thing. That diagram doesn't make sense.

    Here's a picture of the wiring.
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,375
    Can you put your pictures in the post and not links? If you remove your picture it breaks the link. Other people finding this thread looking for help won’t be able to see your pics/wiring diagrams.
    steve
  • JakeCK
    JakeCK Member Posts: 1,356
    Also those are just pictures of the zone valves. Anything of the transformer its self?
  • TheStressMachine
    TheStressMachine Member Posts: 39

    Can you put your pictures in the post and not links? If you remove your picture it breaks the link. Other people finding this thread looking for help won’t be able to see your pics/wiring diagrams.

    Sure, here are the pictures and wiring diagram.




  • JakeCK
    JakeCK Member Posts: 1,356
    Maybe you already have two transformers, with one being just for the zone valves? 
  • TheStressMachine
    TheStressMachine Member Posts: 39
    JakeCK said:

    Maybe you already have two transformers, with one being just for the zone valves? 

    I only found one, would the other one be in the boiler?
  • TheStressMachine
    TheStressMachine Member Posts: 39
    JakeCK said:

    Also those are just pictures of the zone valves. Anything of the transformer its self?

    Here is the transformer
  • JakeCK
    JakeCK Member Posts: 1,356
    edited September 2021
    Thats a separate transformer. open up the front panel of the boiler. you should see one in there. 

    But please make sure to turn off power first!
  • TheStressMachine
    TheStressMachine Member Posts: 39
    JakeCK said:

    Thats a separate transformer. open up the front panel of the boiler. you should see one in there. 

    But please make sure to turn off power first!

    Yes, the "boiler" part of my wiring diagram represent the terminals of the transformer within, sorry I didn't call that out, but the "R, G, C" are on the transformer. Best picture I could swing:

  • JakeCK
    JakeCK Member Posts: 1,356
    If the transformer is powerful enough you could run a common off of that. You are still adding considerably more draw and that transformer is already powering two zone valves. But at least it isn't the boilers transformer.

    Lets see what others think.
  • JakeCK
    JakeCK Member Posts: 1,356
    Heres the official wiring diagram.

  • Jamie Hall
    Jamie Hall Member Posts: 22,117
    If the colourful diagram is correct, yo don't need a fancy relay block. You have everything you need, assuming that your existing transformer can power the Ecobees (it probably can). What you do need to do is to identify positively which wire is which at the Tacos -- and again, I have some doubt as to the wiring diagram there. Your wiring is most like Figure 4 in the Schneider Electric diagrams, and I would expect the wires connected to TR on the Tacos is the common. But test it with a multimeter...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 14,505
    In your wiring diagram L2 is the hot wire, shouldn't matter. Also on the thermostats the wires on W & R should be reversed.

    TH/TR on the valve is a "TIE" point just like a wire nut. It does nothing
    TheStressMachine
  • Zman
    Zman Member Posts: 7,493
    If the original setup is correct, you would get the "C" you need for the t-stat from the TH/TR terminals (just a junction point for the common). I suspect yours is wired backwards, which works fine until you add the smart t-stat to the mix.

    The transformer in the joist bay is the one you should be paying attention to. Are the terminals labeled? It looks like it is a 40VA model. The Zone valve is rated .5 amps (12VA), with 3 zone valves and 2 smart t-stats, you are a little tight on power.

    The wiring diagram in the manual is really confusing, this is what is really going on.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Jamie Hall
    Jamie Hall Member Posts: 22,117
    It was all so simple when a thermostat was a plain vanilla switch... and it worked so well and so reliably... sigh...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    ZmanchiefAlan (California Radiant) Forbes
  • TheStressMachine
    TheStressMachine Member Posts: 39

    If the colourful diagram is correct, yo don't need a fancy relay block. You have everything you need, assuming that your existing transformer can power the Ecobees (it probably can). What you do need to do is to identify positively which wire is which at the Tacos -- and again, I have some doubt as to the wiring diagram there. Your wiring is most like Figure 4 in the Schneider Electric diagrams, and I would expect the wires connected to TR on the Tacos is the common. But test it with a multimeter...

    Thanks! I think my wiring diagram, which represents what I can see, is exactly like figure 4, except I have an extra zone for the boiler and the terminals are double tapped instead of wire nutting like the diagram shows. Other than making sure the common is indeed the common, is there something else you see that is different than figure 4? Again, much appreciated.
  • TheStressMachine
    TheStressMachine Member Posts: 39
    Zman said:

    If the original setup is correct, you would get the "C" you need for the t-stat from the TH/TR terminals (just a junction point for the common). I suspect yours is wired backwards, which works fine until you add the smart t-stat to the mix.

    The transformer in the joist bay is the one you should be paying attention to. Are the terminals labeled? It looks like it is a 40VA model. The Zone valve is rated .5 amps (12VA), with 3 zone valves and 2 smart t-stats, you are a little tight on power.

    The wiring diagram in the manual is really confusing, this is what is really going on.

    Thanks. Terminals aren't labeled, my meter is in another state, but I plan on borrowing one before taking this on.
    Kybeans403
  • TheStressMachine
    TheStressMachine Member Posts: 39
    Thanks everybody for the feedback, here's an upgraded diagram with what I'm going to do
    • Confirm with multi-meter that TR/L1 is indeed neutral.
    • Reverse the wires to the T-Stats so that W energizes TH (and my brain doesn't break when I see white/red together).
    • Upgrade my transformer to 60vac
    • Connect my common wires to TR/L1 (probably right at the transformer terminal)
    Any other feedback?

    Also, I borrowed a multi-meter and realized I won't see negative when testing neutral vs hot because this is AC. I tested both terminals with one wire on something grounded and didn't get full voltage on either, but one of the terminals showed almost a volt while the other showed nothing, I assume almost a volt is my hot? Any other way to confirm hot vs neutral on 24 VAC?



  • HVACNUT
    HVACNUT Member Posts: 5,469
    That diagram isn't correct.
    Your new transformer will have R and C.
    R will connect to TR on the zone valves and RH on the thermostats.
    C will connect to TH/TR on the zone valves and C on the thermostats.
    And something tells me you should wire in an inline 5a fuse, or get a transformer with a circuit breaker. 
    Alan (California Radiant) Forbes
  • Zman
    Zman Member Posts: 7,493
    I like your diagram. L2 is positive and is powering the t stat. W is sending power to TH on the zone valve. motor when there is a call for heat. TR completes the motor circuit back to negative (common) on the transformer. By adding the blue wire, you give the t stat a negative (common) to complete the circuit it needs to operate. Well done, wire away!!
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    TheStressMachine
  • TheStressMachine
    TheStressMachine Member Posts: 39
    edited September 2021
    HVACNUT said:

    That diagram isn't correct.
    Your new transformer will have R and C.
    R will connect to TR on the zone valves and RH on the thermostats.
    C will connect to TH/TR on the zone valves and C on the thermostats.
    And something tells me you should wire in an inline 5a fuse, or get a transformer with a circuit breaker. 

    Wouldn't be surprised if it's not technically correct, just trying to retrofit what I have (everything except the blue wire and T-stat reversal) without getting into too much trouble, but I agree with you that a fuse needs to be present in case I do get into trouble. Seems like your suggestion is essentially reversing the polarity in the system but the end effect of opening and closing of circuits to call on hardware should be the same?

    Is this diagram more in line with what you're thinking? (Dotted red just represents energized only when circuit closed)

  • Jamie Hall
    Jamie Hall Member Posts: 22,117
    You mention reversing polarity -- but this is all AC, so that's not relevant. Usually one side of the 24 VAC transformer is grounded, and that side is usually taken to be common -- but don't count on it. What is important is how the electricity can flow from the transformer, through the control, through the controlled device (or sometimes the other way around) and back to the transformer.

    The point about needing a third wire for the newer thermostats is that they need to have constant power to operate -- and that must be part of a circuit, uninterrupted by anything else, which goes from the transformer to the thermostat and directly back to the transformer. So you have two wires for that -- and the third wire runs through the relay or whatever in the thermostat and feeds power to the valve and then back to the transformer.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • ratio
    ratio Member Posts: 3,544

    Also, I borrowed a multi-meter and realized I won't see negative when testing neutral vs hot because this is AC. I tested both terminals with one wire on something grounded and didn't get full voltage on either, but one of the terminals showed almost a volt while the other showed nothing, I assume almost a volt is my hot? Any other way to confirm hot vs neutral on 24 VAC?

    It sounds (& looks like) the transformer is floating, no actual connection from the secondaries to ground. In that case, the hot & neutral (high voltage names) or R & C (low voltage names) are whichever you pick. If they're marked on the xfrmr I'd use those designations just to make it easy for the next guy, but electrically there's no difference between the two. The boiler should be isolated from that xfrmr by the end switches (TT terminals on the valves) & shouldn't come in to play here. Just make sure that the terminal you pick for C/neutral is landed the same on all the stats & valves.

    NB: if this transformer isn't able to supply both stats, it'd be a lot easier to swap it for a bigger one (higher VA rating) rather than adding one.

    TheStressMachineAlan (California Radiant) ForbesMikeAmann
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 14,505
    If you have 2 wires coming off a 24 volt transformer there really is no hot wire until and unless you ground which ever one you want to be the common. Then when powered up you get 24v between the ywo wires and 24 volts form the hot (ungrounded) wire.

    If the two wires are floating there is no hot IMHO
    TheStressMachineMikeAmann
  • Steamhead
    Steamhead Member Posts: 16,454

    JakeCK said:

    Also those are just pictures of the zone valves. Anything of the transformer its self?

    Here is the transformer
    Where does the 24-volt wire go from this transformer?
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting