Proper Wiring Help Needed

Wiring

I purchased a Honeywell RTH8580WF Wi-Fi Thermostat and now I am not sure if I can use it on my system.  The current thermostat has only two (2) wires on it connected to the RH + W terminals.  I spoke with Honeywell and they tell me I need a third wire (24V) to power the display.  I checked the boiler and the thermostat is connected to a TACO SR503 Zone Control.  I only see two terminals where the current thermostat is connected and I am trying to figure out where the third would connect?

Can anyone help me out here please or would I be better off just returning the new thermostat?

Thanks in advance!

SWEI

Those two terminals

above the transformer have 24VAC on them.

Paul48

Common

I think he needs a Common wire SWEI. Oh...I see what you're talking about now. There's a "C" there.

Techman

wiring

You have a major miswiring problem here. Is that low volt (24v) wiring  going into the same BX as the line volt (120v) wirers? If I'm seeing that correctly , then you have a big problem looming ahead of you and anyone who adjusts the t'stat.

Wiring

I thought it strange

I noticed that when I first opened the cover that the low voltage wires were fed in along with the AC.  I have already disconnected and removed them, feeding them in from the knockout on the opposite side.  I am glad I started this project or I would have never noticed it.  This was installed by a licensed contractor 2-3 years ago and has been that was since.  I have to pull a new wire from the thermostat down in order to get the third wire and just have not had the time as yet.  Thanks all for the info!  If I understand everything correctly, all I need to do is add the wire from the Common terminal of the 24VAC in order to get the new thermostat functioning.

Buster

Proper wiring

The 24vac terminals on the Taco control will go to the RC & C terminals in the thermostat, the existing wires from the Taco control (old thermostat wires) will go to the R & W terminals of the thermostat and remove the metal jumper between R & RC.

Wiring

Thanks

Thank you Buster!  Clear and concise!

STEVEusaPA

End switch

@ techman..Looks like those 2 wires are going to the end switch

Techman

wiring

Hi Steve, the low volt wirers being for the end switch makes good sense. The problem is the insulation value for the lo volt is 300V and 600v for the line volt wirers. So the line volt can "jump " thru any cracks , wear, or worn spots in the insulation , therefore "line volt wire " should have been used for the lo volt circuit if both are run thru the same conduit. We do that all the time. Plus if done on electronic control circuits there can be "interference" in the lo volt wiring due to magnetism.

STEVEusaPA

ahhhhh.....good point

I didnt even look at that because i've never put low and line voltage in the same conduit.

heatpro02920

Everyone does things their own way...

I see the lv and bx ran like that all the time, I don't do it myself because I do it the way I always did it, kind of stuck in my ways. I get on a job and it seems to go super fast when I do it the way I always did it...



And I as well as a lot of other guys will look at a different than our own practice and think its wrong or not as rite, but if its up to code, performs as intended, and the customer is happy with it, then its good...



I had people comment about how I wire in a zone valve control on a retrofit, since the wries are never long enough to reach the control I mount my control, then run 18-5 up to the zone valves, tie red and white into the t-stat wires and tire the blue, green, and yellow into 1, 2, and 3 on the zone valve... I strip the 18-5 back around 8 inches and put a couple screwdriver loops in the r,w and then the b,g,y it looks good when its done, IMO, its fast, convenient, and works well for me... Now a tech that works for me and a friend of mine in the field like to put a handy box in the ceiling and connect all the t-stat wires in there with new longer extensions that go to the control, then run 18-2 for that and 18-3 to each zone valve.... To me it takes too long, doesn't look as good, costs more in materials, and gets confusing when servicing...



I know a contractor that runs all his t-stats in one cable up to the ceiling {no box} then connects them all to a single cable and then runs 18-3 to each zone valve, so if he has 5 zones he runs 18-10 {10 different wires} for all the tstats and then wires each one, the wire he uses has double colors, so it for 18-10 it will be blue and then blue with a white stripe, then orange and orange with a white stripe, ect so each color is its own zone, then he puts a piece of that color electric tape on the zone that corresponds to it so the zone valve that he used for the orange wires gets some orange tape....



To me it all works, but I like my way...

Techman

Lo volt vs line volt

But it is against code to run both wirers in the same conduit. Put the 24v into "line volt wirers " and it is legal. Look inside control panels, relays boxes , zone panels and there is a "divider" (usually gray colored cardboard) between the two voltages separating them from each other. Look at the RIB relays, they use all "line volt" wirers.Look at AC cond units, lo volt wirers(24v) connect to line volt wirers(24v) then the lo volt circuit goes thru hi/lo press switches, the Copeland "staging control" or "time delay relays" or any other controls.

HeatBudy

I'm a new bee to all this but this is what I found out after research. If you have a Taco SR503 switching relay and your current system is a 2-wire, and you are looking to add a smart thermostat Honeywell. Then you will have to do the following,
If your only have two wires you will need to upgrade, if you have 3 wires or more you are ok..
Let me say this first.. I am only talking about a heat only system, if you have A/C then you will need more than 3 wires anyway.
1st. upgrade your wiring to 3 wires or you can get one of those add a wire devices, but I am not speaking to that option.
2nd Once the wire is in place or you already had more than two wires. you will need to connect a C or common wire to the Taco SR503. remove the cover on the RS503 to the right of the zones I have 3 zones you will see a connection labeled 24vac on one side and com on the other side.
3rd. take the blue wire and connect it to the ( com ) side - this is the hot side that has the 24volts need to power your thermostat. If you have only one zone let's say then you will have a white wire to the (W) a red wire the the (R). for zone 1.
Now take the blue wire and connect it to the com port.. If you don't have blue pick another color. So now lets go to the thermostat,
I just did a Honeywell smart thermostat and I think the layout is the same for the Honeywell smart thermostats.. remove the old thermostat make sure you mark your wires or at lease know it's letter i.e. W or R or Y or what ever.
Heat only system will have two wires most likely W and R. put the new mounting plate up for the thermostat, connect the wires as followed.
The White wire to the terminal marked W,
The Red wire to the terminal marked R
and the new wire to the terminal marked C.
put the cover on power up your unit and you should be good to go.

vaporvac

@HeatBudy‌ , you should write their manuals! I 'm using your system to look over my wiring at the Tstat tomorrow. Thank you.

NeedAdvice

Heatbudy,

How is this done when you have two or more zones with a taco relay and only one com port. Thanks

Chamkila

NeedAdvice said:

Heatbudy,

How is this done when you have two or more zones with a taco relay and only one com port. Thanks

Same question, i have 2 zones and 2 different thermostates, can i run these two on the same 24vac terminals? with 2 wires each in each terminal? Thanks

Chamkila

Buster said:

Proper wiring

The 24vac terminals on the Taco control will go to the RC & C terminals in the thermostat, the existing wires from the Taco control (old thermostat wires) will go to the R & W terminals of the thermostat and remove the metal jumper between R & RC.

Can you help with the question above please. Thanks

billtvt

Same question- I have two Nest (gen 3) tstats that I need to run common wires to Taco SR506. Can I put 2 common wires in the same terminal on this board? Since there is only one Com terminal- I need to know if that is workable or what my alternative is (ie standalone transformer?)

Thanks

Paul48

You need the right sr506
https://www.taco-hvac.com/uploads/FileLibrary/102-365.pdf

billtvt

Thanks. I've seen the newer ones that have the common connections, but really don't want to mess with replacing my current 506. There must be some way to add a second common wire to the board? Can I share the single common connection?

Jamie Hall

The common -- as the name implies -- can be shared. However. You cannot put two wires under one screw if you really want to do it right. Put one wire under the connection which is a short pigtail, then splice the lot of them together.

billtvt

Thanks Jamie- I will try that- makes perfect sense.