The ecobee3-lite-Technical-Specifications state the power requirements are 3.5 VA. I am not sure why the tech support person is saying you need a transformer rated at least 20 VA. Are you sure the rating for the relay is 15 VA (which 15 watts) and not 15 A (which is 15 amperes)? I am not a switching relay expert, but I believe these devices specify the total amount of current the relays can supply when closed. The power dissipation when all the relays are closed should be small.

You can use an ohm meter to determine if the wires are spliced. Disconnect the wires at each end and verify it is open circuit. Then connect two wires at one end and verify they are shorted together at the other end. If you don't have an ohm meter you could try a battery and a low voltage light bulb.

The top of the transformer reads 15VA (i think). Picture pasted below.

I like the idea with the battery/low voltage light. Would I just connect the + battery end to the wire and then hold like a christmas light bulb to the other end?

I'm assuming the green wire on the Taco end splices with a red wire on the thermostat end. What is the easiest way to test is that is one continuous wire? Both wires are currently not connected to anything.

Oh, so there's a red wire on the thermostat end. I missed that in your question.

If you have a multimeter, you could do resistance (ohm) tests by twisting various combinations of wires together on the thermostat end and measuring the resistance of the resulting loop on the Taco end.

But why not just assume the red wire on the thermostat end is connected to the green wire on the Taco end:

1. On the Taco board, attach the green wire to the COM screw-down terminal.
2. On the ecobee, attach the black (Taco red) wire to the Rc connector, the white wire to the W1 connector, and the red (Taco green) wire to the C connector. If the ecobee fires up, you're good to go.

The top of the transformer reads 15VA

You are correct. I imagine this transformer has been sized so it can power three thermostats and the all relays at the same time. You are only connecting one thermostat. There should be no issue with connecting the one Ecobee thermostat.

I like the idea with the battery/low voltage light. Would I just connect the + battery end to the wire and then hold like a christmas light bulb to the other end?

You need a light bulb that will light up with a battery. An led flash light battery would work. You would be better off investing in a multimeter. The one suggested above is a nice one for only $30. Home Depot also sells an analogue type for $13 if you want to spend less money. They are easy to use and can be used to measure voltages in case you connect everything and the thermostat does not work.

spoke to Taco and Ecobee, both said my current 15VA transformer would not be sufficient to power the 3.5amps the Ecobee with demand. is there a way to run a c wire or power supply behind the wall w/o plugging in an external transformer?

I disagree with Taco and Ecobee customer support. If the Ecobee3 Lite actually required 3.5 amps then with a 24 V power the supply it would be dissipating 84 W. If you had the multimeter and some wire you could attach it to the thermostat and see the current is much less. They are saying the current transformer is too small and you have to install a larger one. The choices are replacing the Taco relay or installing a separate transformer for the Ecobee3 Lite.

If I thread the green wire to the COM terminal and attach to the thermostat and it is too much power(as Ecobee/Taco say), would that blow the whole circuit board?

Also, what is the difference between the 24VAC terminal and the COM terminal?

"spoke to Taco and Ecobee, both said my current 15VA transformer would not be sufficient to power the 3.5amps..."

No. The specs state that the ecobee uses less than 3.5 VA. Your transformer provides 15 VA.

"too much power"

I don't know what that means. I think the only thing that's important is that the ecobee receive the proper voltage, 24 VAC, which is what those screw-down terminals provide.

"Also, what is the difference between the 24VAC terminal and the COM terminal?"

Nothing. The two screw-down terminals are connected together and provide 24 VAC. Taco just labeled the lower terminal "COM" aka "Common".

-- amateur

So I wire the green to COM and red to Ecobee... made up scenerio.. let's say the Ecobee uses 10amps, would that fry my board/ruin the taco relay or would the Ecobee just not ppwer up because it isnt drawing the amerage from the relay.  What is my risk in just wiring it with the current setup and turning the Ecobee on

"let's say the Ecobee uses 10amps"

Why would you say that? The specs say the ecobee uses less than 3.5 VA.

-----

Single phase VA to amps calculation formula

The current I in amps is equal to the apparent power S in volt-amps, divided by the voltage V in volts:

I(A) = S(VA) / V(V)

0.1458A = 3.5VA / 24V (Your ecobee uses less than 0.15 amps)

"Why would you say that?"

I am trying to figure out what would happen if the power ask from the Ecobee is too high (as both Ecobee and Taco seem to believe). Could the Taco relay break/fry/etc... or will the Ecobee just not be provided with enough power to function. That is why I used a high number as an example, to see what my risk is here.

my transformer, 24V / 15VA, is rated to supply 0.625 amps. if Ecobee is demands 0.15 amps, I am left with max output of 0.475. I am not sure how many amps my relay requires to function.

here is the post from Ecobee support:

"The Taco SR503-4 Zone Switching Relay has a built-in 24V transformer that is only sufficient in rating to supply voltage to the Zone Control."

"...with the power requirements of one or more ecobee3 thermostats this transformer will be insufficient in capacity. As a result another external transformer will be needed to power the thermostats and an isolation relay per zone to connect to the R & W terminals of each zone."

Cut and strip the ends of three wires. Connect them to the Taco board and ecobee. If everything works, leave the thermostat connected for a few hours. If everything still works, install the thermostat.

You are only connecting one thermostat. If you were connecting three you could exceed the power maximum power limit.

I agree with wdccruise. That Ecobee T-stat is drawing 150mA! That’s almost nothing in the scheme of things there, the T-stat represents virtually no load since it’s not driving (powering) anything! It’s only a fancy low voltage digital switch.

You worried about nothing with regard to the transformer. Just get the rest of the wiring right, forget the transformer and you ‘should be’ alright.

I’m not providing any guarantees - just logic!

IMPO

SR

Why do you have a 3 zone capable zoning board only using 1 zone input? (controlling a single zone via a 3 zone board?)

Yet you're using all 3 outputs of that zone board? Why? What does this system control?

If you're only using one zone why use the zone control board? OR are you trying to do something because you simply do not know? Spell it out what you're trying to do more than just trying to make something work because you "think it should".

Zoning only looks simple on the surface, much more to it that meets the "eye".

I know HVAC zoning... I service the Katy, Texas area.

pretty simple answer, because that is what the person who built the house installed (assuming it was put there for future growth plans)

I am specifically trying to install a smart thermostat and trying to determine if there is any danger to causing a fire or fry the board.

You're driving yourself crazy. Just wire it up.

lol I am going to, just answering people who are responding.

a 3 zone board only using a single zone isn't installed for "future growth".

If you are only using a single zone, you don't need the 3 zone board.

Example of a zoning system in your home: light switches in every room. They are "zoned" to a room so you can shut the lights off if no one is in there.

You wouldn't install 3 light switches in 3 different rooms and then "not hook them up" claiming --- it's for future growth when we want to run wires so we can shut off the lights.

LOL, is right my man.

I didn't install it and as mentioned above I ASSUMED for future growth. The previous owners were finishing the basement and 2nd floor. So I ASSUME(there's that word again) they were planning on adding a thermostat in the basement and 2nd floor. 3 zones, "future growth". Very simple concept that makes sense, but there weren't any questions on my zones, it was on installing a new thermostat and if my system has the electrical capacity. I am not sure why you are posting on this thread if you are not answering the questions being asked.

your example is not comparing apples to oranges, not the same situation. in your own words, LOL, is right my man.

Chris: Just ignore @Austin Air Companie.

I have zero electrical experience, that is why I am here... trying to learn, not deal with a know it all that is not helping at all... If you have read the thread you will see that I am very into making sure something works, that is why I have called Ecobee, Taco and started a thread on a few boards AND have not done anything yet, bc i am not 100% sure. I wish I could get an electrician or HVAC guy here, but they are all booked out until 2045.

"...But the manufacturer tells you it won't work and so your goal is to ignore them too?"

You're making a lot of assumptions without knowing the full story. Taco says go for it, Ecobee says no.

Called Taco back and they said it will work as long as under 2 amps. The manufacturer of the relay said it is fine, while the tech support of Ecobee overseas read there manual and disclaimer and said they wouldn't recommend with the current transformer.

and btw, you still haven't been any help whatsoever...

You're making a lot of assumptions without knowing the full story. and btw, you still haven't been any help whatsoever...

It is your job to tell me the full story, not my job to "play guessing games".

You can't be "helped" without knowing fully what you are trying to do. If Taco said go for it, will they warranty the board if you fry it? Uh, no. What do they have to lose? --- you'll have to buy another board.... or they will refer you to a contractor, most likely.

My job involves looking at the whole job, not just bits and pieces of it and then lets sit back and hope it works? Your spincter muscle has got to be in knots, wrapped so tightly around your wallet it's making you delusional.

No one will help you over come that.... it starts with you.

not sure what my sphincter*(might want to use spell check) or wallet have to do with this, but I am thankful both are fully functional. Typical off topic and of no help response...

I've told the "story" and EVERYONE else on this board has been helpful so far, except you. You still have not helped whatsoever.

I can deduce that you think it is a bad idea and you could have just left it at that. I have not done this myself yet and am waiting on an electrician or HVAC guy to call me back because I am not fully comfortable at the moment and as you mentioned above..I do not want to cause more harm then good(i.e. frying the board).

I suggest you stop making assumptions, because you have been wrong every time. I also suggest you not replying on this thread unless you are going to provide something of use.

Hey folks. Maybe I can explain this a little better.

The transformer in the Taco SR503 is rated at 24VAC at 15 VA which translates to about 0.625A. This has to power all the relay coils (3 of them) plus the LEDs. Taco is saying the transformer is only providing enough power for when all three relays are on (calling for heat), plus the 4 LEDs. Assuming standard engineering practice of providing up to 50% more power than continuously required, the transformer may be able to provide the additional 150 mA (3.6 vA @24VAC). That is only an assumption.

I looked up the 24VAC LY2 Omron relay specifications and it consumes upto 1.2VA when actuated. Since there are 3, that's a minimum of 3.6VA power required when all zone relays are on. So for those who say "wire it up and try it", it could work using a total of 7 or 8VA or maybe a little more with the resistors and LEDs on the board, which is still under the transformer's 15VA rating.. The transformer will run a little hotter, but I doubt the 1A fuse will blow. The fuse is a fast blow and over time, as it runs hotter than designed, it may fail and knock out all heat. Just hope it doesn't happen in the dead of winter.

If you plan to test it, make sure you turn on all zone thermostats for a good long while to draw max current.

If you're skilled enough, put your multi meter into ammeter mode and put the probes in place of the fuse to see how much AC current is actually being drawn when all zones are firing. (should be mAmps). If you exceed 660 mA, your transformer will run hot because it is rated only for that much continuous power max. (This would be bad.)

Since I'm in the same boat, I plan to measure it when one zone is calling and multiply it by 3 for total load when all three zones are calling. If I have 300 mA to spare, I'll use the Taco to supply my C-wire, thus ensuring an adequate power budget from the 15VA transformer.

I'm no expert, but I hope this helps more than confuses...